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MUHS 2nd MBBS - MICROBIOLOGY - PAPER 1

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LAQ SECTION

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Q1. 5-year-old female: abdominal pain, weight loss, perianal itching

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i) Likely Parasite (2 marks)

• Age: 5 years (children most affected)
• Perianal itching (pathognomonic) - especially at night
• Abdominal pain + weight loss

• Phylum: Nemathelmintha
• Class: Nematoda
• Habitat: Caecum, appendix, large intestine

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ii) Life Cycle (3 marks)

┌──────────────────────────────────────────────────────────┐
│              LIFE CYCLE OF E. VERMICULARIS               │
│                                                          │
│  INFECTIVE EGGS (ingested)                               │
│       ↓  (Mouth → stomach → small intestine)            │
│  LARVAE HATCH in duodenum                                │
│       ↓  migrate to large intestine                      │
│  ADULT WORMS develop in caecum/colon                     │
│  (Male + Female mate in large intestine)                 │
│       ↓                                                  │
│  Gravid FEMALE migrates to perianal region at night      │
│       ↓  lays 10,000-15,000 eggs                         │
│  EGGS deposited on perianal skin                         │
│  → become infective within 6 hours                       │
│       ↓  (Scratching → hand → mouth)                     │
│  RE-INGESTION / AUTO-INFECTION                           │
│       ↓                                                  │
│  Retrograde infection also possible (rare)               │
└──────────────────────────────────────────────────────────┘

• No intermediate host
• Infective form: embryonated egg (with larvae inside)
• Mode of infection: Feco-oral, hand-to-mouth (auto-infection)
• Time from egg ingestion to adult maturity: 2-4 weeks
• Retroinfection: eggs hatch on perianal skin, larvae re-enter via anus
• Ectopic sites: vagina, uterus, fallopian tubes, peritoneum (in girls)

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iii) Labelled Diagram of Parasite and Egg (3 marks)

╔══════════════════════════════════════════════════════╗
║        ENTEROBIUS VERMICULARIS - ADULT WORMS         ║
║                                                      ║
║  FEMALE (10 mm):           MALE (3-5 mm):            ║
║  ┌──────────────┐          ┌──────────┐              ║
║  │ Cervical     │          │          │              ║
║  │ alae (wing-  │◄HEAD     │    HEAD  │              ║
║  │ like)        │          │    ↓     │              ║
║  │ Esophagus    │          │  CURVED  │              ║
║  │ with bulb►───┤          │POSTERIOR │              ║
║  │              │          │  end     │              ║
║  │ Long pointed │          │(single   │              ║
║  │ POSTERIOR ──►│          │spicule)  │              ║
║  │ end          │          └──────────┘              ║
║  └──────────────┘                                    ║
║                                                      ║
║  KEY: Cervical alae = cephalic alae (both sexes)     ║
║       Female has POINTED TAIL (pin-shaped)           ║
║       Male has CURVED TAIL                           ║
╚══════════════════════════════════════════════════════╝

╔══════════════════════════════════════════════════════╗
║           ENTEROBIUS EGG - EASY TO DRAW              ║
║                                                      ║
║        ╔══════════════════╗  ← Thick shell           ║
║        ║  ___________     ║                          ║
║        ║ /  EMBRYO   \    ║  ← Larva visible inside  ║
║        ║|   (coiled   |   ║                          ║
║        ║ \  larva)   /    ║                          ║
║        ║  -----------     ║                          ║
║        ╚══════════════════╝                          ║
║                                                      ║
║  Shape: PLANO-CONVEX (asymmetrical)                  ║
║         = D-shaped / football-shaped                 ║
║  Size: 50-60 x 20-30 μm                              ║
║  ONE side FLAT, OTHER side CONVEX                    ║
║  DOUBLE-WALLED shell                                 ║
║  Contains coiled larva (infective stage)             ║
╚══════════════════════════════════════════════════════╝

Exam tip: The FLAT-CONVEX shape of the egg is PATHOGNOMONIC - no other helminth has this egg shape.

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iv) Lab Diagnosis

• Preferred method
• Transparent sticky tape applied to perianal skin early morning BEFORE bathing or defecation
• Tape placed on glass slide, examined under microscope
• Reveals characteristic plano-convex eggs
• Repeat on 3 consecutive mornings to improve sensitivity

• Wooden spatula with cellophane tape used to swab perianal area
• Examined microscopically

• Routine stool O&P: adult worms may be seen (less sensitive for eggs)
• Eggs rarely found in stool (laid outside in perianal region)

• Thread swallowed, retrived, examined for adherent eggs

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Q2. 6 children, 9-10 years, rice-watery diarrhea, vomiting, no pus cells, darting motility

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i) Probable Organism

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ii) Etiological Agent

• Alkaliphilic - grows best at pH 8.5-9.5
• TCBS agar (Thiosulfate Citrate Bile Salts Sucrose) - yellow colonies (sucrose fermenter)
• Peptone water - forms surface pellicle
• Blood agar - beta-hemolysis (El Tor biotype)
• Non-halophilic (unlike other Vibrios)

• Classical biotype (original)
• El Tor biotype (currently predominant, 7th pandemic)

• Cholera toxin (CT) - A-B type exotoxin (most important)
  • B subunit (5 subunits): binding to GM1 ganglioside on enterocytes
  • A subunit: activates adenylyl cyclase → ↑↑ cAMP → massive Cl⁻ secretion + inhibits Na⁺ absorption → massive water loss
• Toxin co-regulated pilus (TCP) - colonization factor
• Neuraminidase - converts GM2 → GM1 (more receptor exposure)

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iii) Lab Diagnosis

• Wet mount: Comma-shaped, highly motile organisms - darting motility
• "Hanging drop" preparation shows typical darting/shooting star motility
• Immobilization test: Motility inhibited by O1 antiserum (diagnostic)

1. Alkaline peptone water (APW) pH 8.6 - enrichment broth (incubate 4-6 hrs)
2. TCBS agar - yellow colonies of V. cholerae O1
3. Gelatin stab: Infundibuliform (funnel-shaped) liquefaction
4. Blood agar: Beta-hemolysis (El Tor), non-hemolysis (Classical)

• Oxidase positive (key feature - unlike Enterobacteriaceae)
• Indole positive
• String test positive (0.5% sodium deoxycholate → viscous string)
• Voges-Proskauer: El Tor +ve, Classical -ve
• Chicken cell agglutination: El Tor +ve

• Slide agglutination with O1 polyvalent antiserum
• Differentiate Ogawa (A+B) vs Inaba (A+C)

• Dipstick/lateral flow immunoassay (Crystal VC, SD Bioline) - for field use
• Multiplex PCR

• Identifies organism directly in stool

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iv) Management

SEVERITY ASSESSMENT:
                    ↓
    Mild/No dehydration → ORS (oral rehydration solution)
                    ↓
    Moderate dehydration → ORS aggressively
                    ↓
    Severe dehydration → IV Ringer's Lactate (100ml/kg)
                         WHO regimen: 30ml/kg in 30 min, then 70ml/kg in 2.5 hrs

• WHO ORS: NaCl 3.5g + KCl 1.5g + NaHCO3 2.5g + Glucose 20g in 1 liter water
• Rice-based ORS is superior

• Adults: Doxycycline 300mg single dose (drug of choice)
• Children: Azithromycin 20mg/kg single dose
• Alternatives: Cotrimoxazole, Ciprofloxacin

• 20mg/day for 10-14 days

• Identify source (water/food)
• Notify public health authorities
• Quarantine contacts
• Safe water supply, proper sanitation
• Boil water advisory

• Dukoral (oral killed whole cell + CTB) - 2 doses
• Shanchol (bivalent oral inactivated) - 2 doses

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Q3. RT hypochondrial tenderness, fever, WBC 16,000, SGPT 247, SGOT 285, USG: single abscess postero-superior liver

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i) Probable Pathogen

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ii) Lab Diagnosis

• ELISA for anti-amoeba antibodies - sensitivity ~95%
• IHA (Indirect Hemagglutination Assay) - titre >1:256 significant
• Counter Immunoelectrophoresis (CIE)
• Latex agglutination test

• Wet preparation: look for motile trophozoites with ingested RBCs
• Stool microscopy positive in only 30-40% of ALA cases
• Cysts in formed stool

TROPHOZOITE features (diagnostic):
- Size: 12-60 μm
- Motility: Directional (unidirectional), progressive with finger-like pseudopodia
- INGESTED RBCs in cytoplasm (pathognomonic)
- Ectoplasm (clear) and endoplasm (granular) visible

• Pus: Anchovy sauce appearance (brownish, thick)
• Trophozoites found at PERIPHERY of abscess (not in pus)
• Gram stain: No organisms usually (sterile unless secondary bacterial infection)
• Send for: wet mount, ZN stain, C&S (to rule out pyogenic)

• Leukocytosis (WBC 16,000 as in this case) - polymorphonuclear predominance
• SGPT/SGOT elevated (hepatocellular damage)
• ALP markedly elevated
• Blood culture negative (unlike pyogenic)

• USG: single well-defined hypoechoic lesion, right lobe, postero-superior = classic ALA
• CT scan: low-density lesion with peripheral enhancement
• MRI: T2 hyperintense lesion

• Stool antigen ELISA (TechLab E. histolytica II test) - detects Gal/GalNAc lectin

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iii) Life Cycle (3 marks)

╔═══════════════════════════════════════════════════════════════╗
║        LIFE CYCLE OF ENTAMOEBA HISTOLYTICA                    ║
║                                                               ║
║  MATURE QUADRINUCLEATE CYST (infective form)                  ║
║       ↓ [Ingested via contaminated food/water]                ║
║  STOMACH → resistant to gastric acid                          ║
║       ↓                                                       ║
║  SMALL INTESTINE → EXCYSTATION                                ║
║       ↓ [metacystic trophozoite forms]                        ║
║  METACYSTIC TROPHOZOITE (8 nucleate → 8 trophozoites)         ║
║       ↓                                                       ║
║  LARGE INTESTINE (cecum, ascending colon)                     ║
║       ↓                                                       ║
║       ├── COMMENSALISM:                                       ║
║       │   lives on luminal surface → CYSTS formed             ║
║       │   → passed in stool → continue cycle                  ║
║       │                                                       ║
║       └── INVASION (pathogenic route):                        ║
║           ↓ [penetrate mucosa via cytotoxin + proteases]      ║
║       FLASK-SHAPED ULCER in colon                             ║
║       ↓                                                       ║
║       ├── AMOEBIC DYSENTERY (intestinal)                      ║
║       │                                                       ║
║       └── BLOOD VESSEL INVASION                               ║
║           ↓ [portal vein]                                     ║
║       LIVER → AMOEBIC LIVER ABSCESS                          ║
║           ↓ [transdiaphragmatic spread]                       ║
║       LUNG, BRAIN, SKIN (rare)                                ║
║                                                               ║
║  CYST FORMS: 1-nucleate → 2-nucleate → 4-nucleate (mature)    ║
╚═══════════════════════════════════════════════════════════════╝

• Size: 10-20 μm
• Shape: Spherical
• Nuclei: 1 to 4 (mature cyst = 4 nuclei)
• Chromatoidal bars: rounded/cigar-shaped ends (vs. E. coli: splinted ends)
• Glycogen mass: present in young cysts (stains brown with Lugol's iodine)

• Metronidazole 800mg TID x 10 days (drug of choice for invasive disease)
• Tinidazole 2g OD x 3 days
• Followed by luminal agent: Diloxanide furoate 500mg TID x 10 days (to eliminate intestinal cysts)
• Drain abscess if: >5cm, risk of rupture, failed medical therapy

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SAQ SECTION

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SAQ 1: Bacterial Growth Curve and Applications

Four Phases:

╔══════════════════════════════════════════════════════════════════╗
║                 BACTERIAL GROWTH CURVE                          ║
║                                                                  ║
║  Log        │          ___________                               ║
║  viable     │         /           \  STATIONARY                  ║
║  cell       │        /             \────────────────DEATH        ║
║  count      │       /               (plateau)      \            ║
║             │  ____/ EXPONENTIAL                    \           ║
║             │ LAG  (log)                              ↘          ║
║             └──────────────────────────────────────────         ║
║                        TIME →                                    ║
╚══════════════════════════════════════════════════════════════════╝

Applications of Growth Curve:

1. Antibiotic therapy: Log phase bacteria most susceptible to cell-wall synthesis inhibitors (penicillin, cephalosporins)
2. Vaccine production: Organisms harvested at log phase (maximum viable count, maximum antigenicity)
3. Industrial fermentation: Antibiotics, enzymes harvested in appropriate phases
4. Sterilization protocols: Understanding death kinetics helps calculate D-value and sterilization time
5. Epidemiology: Incubation period of diseases correlates with growth phase
6. Culture media optimization: Determining generation time of organisms
7. Antimicrobial susceptibility testing (MIC, MBC): Inoculum standardized to log phase

• E. coli: 20 min
• S. aureus: 30 min
• M. tuberculosis: 18-24 hours (explains slow disease progression)

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SAQ 2: Methods of Horizontal Gene Transfer (HGT) - describe one in detail

Three Main Methods:

╔══════════════════════════════════════════════════════════════╗
║         HORIZONTAL GENE TRANSFER - OVERVIEW                  ║
║                                                              ║
║   1. TRANSFORMATION          2. TRANSDUCTION                 ║
║   ┌──────────────┐          ┌──────────────────────┐         ║
║   │ Donor cell   │          │  Bacteriophage picks  │        ║
║   │ lyses →      │          │  up donor DNA →       │        ║
║   │ naked DNA    │          │  injects into         │        ║
║   │ released →   │          │  recipient cell       │        ║
║   │ recipient    │          └──────────────────────┘         ║
║   │ takes up DNA │                                           ║
║   └──────────────┘                                           ║
║                                                              ║
║   3. CONJUGATION (Cell-to-cell contact)                      ║
║   ┌──────────┐                ┌──────────┐                   ║
║   │ DONOR    │──sex pilus────►│ RECIPIENT│                   ║
║   │ (F+/Hfr) │ ←conjugation  │  (F-)    │                   ║
║   │          │  bridge        │          │                   ║
║   └──────────┘                └──────────┘                   ║
╚══════════════════════════════════════════════════════════════╝

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CONJUGATION - IN DETAIL (most important clinically):

• Donor cell: must carry F (fertility) plasmid (F+ cell) or Hfr (High frequency recombination)
• Recipient: F- cell
• Physical contact through sex pilus (conjugation tube/bridge)

Step 1: F+ donor cell extends sex pilus (F pilus) toward F- recipient
Step 2: Pilus contracts → cells drawn together → conjugation junction formed
Step 3: One strand of F plasmid DNA is nicked at oriT (origin of transfer)
Step 4: Single strand transferred 5'→3' through conjugation bridge
Step 5: Complementary strands synthesized in BOTH cells
Step 6: Recipient becomes F+ (now can transfer to others)

• R plasmids (Resistance plasmids): carry multiple antibiotic resistance genes
• Single conjugation event → multi-drug resistance spread to entire bacterial population
• Example: MRSA resistance, ESBL-producing E. coli
• Responsible for epidemic antibiotic resistance spread in hospital settings

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SAQ 3: Blood Spill Management

Immediate Steps:

BLOOD SPILL ON SKIN:
1. Do NOT panic
2. Wash with soap and water for 10-15 minutes
3. Do NOT scrub/squeeze the wound
4. Do NOT use harsh antiseptics (bleach)
5. If mucous membrane (eye/mouth): flush with copious water/saline
6. Report to infection control officer IMMEDIATELY

Steps for Blood Spill on Environmental Surface:

STEP 1: PERSONAL PROTECTION
        → Wear gloves, mask, gown, eye protection

STEP 2: DECONTAMINATION
        → Cover spill with paper towels/cloth
        → Pour 1% Sodium Hypochlorite (bleach) solution over it
        → Leave for 30 minutes (contact time)
        → Clean up with fresh paper towels (outward-inward circular motion)
        → Discard in biohazard bag (yellow bag)

STEP 3: SECOND CLEAN
        → Mop area with detergent/water

STEP 4: WASTE DISPOSAL
        → All material in biohazard bag
        → Dispose as biomedical waste

STEP 5: HAND HYGIENE
        → Remove gloves carefully (glove-in-glove technique)
        → Wash hands with soap and water 6-step WHO method

• Routine decontamination: 0.5% (5000 ppm) hypochlorite
• Large spills: 1% (10,000 ppm) hypochlorite
• Contact time: Minimum 30 minutes

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SAQ 4: Steps in NSI (Needle Stick Injury)

• HIV: 0.3% per exposure
• HBV: 6-30% per exposure (highest risk)
• HCV: 0.5-1.8% per exposure

IMMEDIATE STEPS (within seconds-minutes):

┌─────────────────────────────────────────────────┐
│ STEP 1: FIRST AID (IMMEDIATE)                   │
│ • Do NOT squeeze/suck the wound                 │
│ • Allow blood to flow freely (encourage)        │
│ • Wash with soap and water for 10-15 min        │
│ • Apply antiseptic (povidone-iodine/70% alcohol)│
│ • If eyes/mouth: flush with water/saline        │
│                                                 │
│ STEP 2: REPORT (within 1-2 hours)               │
│ • Report to infection control officer           │
│ • Fill NSI reporting form                       │
│                                                 │
│ STEP 3: ASSESS SOURCE PATIENT                   │
│ • HIV status (with consent)                     │
│ • HBsAg, Anti-HCV                               │
│ • Note: Do NOT delay PEP waiting for results    │
│                                                 │
│ STEP 4: BASELINE TESTING OF INJURED HCW         │
│ • HIV serology (at 0, 6 weeks, 12 weeks,        │
│   6 months)                                     │
│ • Anti-HBs titre                                │
│ • Anti-HCV                                      │
│                                                 │
│ STEP 5: POST-EXPOSURE PROPHYLAXIS (PEP)         │
│ HIV PEP (start within 2 hours, max 72 hrs):     │
│ → TDF + FTC + LPV/r (or RAL) x 28 days         │
│                                                 │
│ HBV PEP:                                        │
│ → If vaccinated + immune: No action             │
│ → If not vaccinated: HBIG 0.06ml/kg IM +        │
│   Hepatitis B vaccine series                    │
│ → If vaccinated, no response: HBIG x 2 doses    │
│                                                 │
│ HCV PEP: No effective PEP available             │
│ → Monitor HCV RNA at 4-6 weeks                  │
│                                                 │
│ STEP 6: FOLLOW UP                               │
│ • Counselling                                   │
│ • Repeat serology as per schedule               │
│ • Report final outcome                          │
└─────────────────────────────────────────────────┘

• Type of injury (deep vs. superficial)
• Type of device (hollow-bore needle = highest risk)
• Volume of blood inoculated
• Source patient viral load
• Immunization status of HCW

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SAQ 5: Note on Autoimmunity

Normal Self-Tolerance Mechanisms:

1. Central tolerance: Clonal deletion of self-reactive T cells in thymus (negative selection), B cells in bone marrow
2. Peripheral tolerance: Clonal anergy (no co-stimulation), Regulatory T cells (Tregs), immune ignorance

Mechanisms of Autoimmunity (how tolerance breaks down):

╔══════════════════════════════════════════════════════════════╗
║            MECHANISMS OF AUTOIMMUNITY                        ║
║                                                              ║
║  1. MOLECULAR MIMICRY                                        ║
║     Microbial antigen → similar to self-antigen              ║
║     Ex: Streptococcal M protein → cardiac myosin             ║
║         (Rheumatic fever)                                    ║
║                                                              ║
║  2. POLYCLONAL ACTIVATION                                    ║
║     EBV, superantigens → non-specific activation             ║
║     of self-reactive B/T cells                               ║
║                                                              ║
║  3. BYSTANDER ACTIVATION                                     ║
║     Inflammation → release of sequestered antigens           ║
║     → activated APCs present self-antigens                   ║
║                                                              ║
║  4. EPITOPE SPREADING                                        ║
║     Initial immune response → damage →                       ║
║     exposes new self-epitopes → expanded response            ║
║                                                              ║
║  5. REGULATORY T CELL DEFICIENCY                             ║
║     Loss of Tregs → unchecked self-reactive clones           ║
║                                                              ║
║  6. SEQUESTERED ANTIGEN RELEASE                              ║
║     Eye lens, sperm, brain antigens normally hidden          ║
║     → trauma exposes them → immune attack                    ║
║     Ex: Sympathetic ophthalmia, orchitis                     ║
╚══════════════════════════════════════════════════════════════╝

Classification of Autoimmune Diseases:

Examples of Autoantibodies (High yield):

• SLE: Anti-dsDNA, Anti-Sm (specific), ANA
• RA: Rheumatoid Factor (IgM anti-IgG), Anti-CCP
• Myasthenia gravis: Anti-AChR antibodies
• Pemphigus vulgaris: Anti-desmoglein antibodies
• Graves' disease: TSI (thyroid stimulating immunoglobulin)
• Hashimoto's: Anti-TPO, Anti-thyroglobulin

Role of HLA in Autoimmunity:

• HLA-DR3/DR4 → Type 1 DM
• HLA-B27 → Ankylosing spondylitis
• HLA-DR4 → Rheumatoid arthritis
• HLA-DQ2/DQ8 → Celiac disease

Factors predisposing to Autoimmunity:

• Genetic: HLA haplotype, family history
• Gender: More common in females (sex hormones)
• Environmental: Infections (molecular mimicry), drugs (drug-induced lupus), UV radiation
• Age: Varies with disease

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Source references: Jawetz, Melnick & Adelberg's Medical Microbiology 28th Edition; Murray's Medical Microbiology 9th Edition; Apurba Shastri's framework for MUHS examination pattern.

MUHS Exam tip: For LAQs, always begin with "Definition/Classification," then proceed to morphology/life cycle/lab diagnosis/treatment. For SAQs, use clear headings, tables, and diagrams. Time management: LAQ ~15 min each, SAQ ~7-8 min each.

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MUHS 2nd MBBS - MICROBIOLOGY - PAPER (Qs 6-21)

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Q6. PRESCRIPTION - NOTE WITH APPLICATIONS

Parts of a Prescription:

╔══════════════════════════════════════════════════════════════════╗
║                    PARTS OF PRESCRIPTION                         ║
║                                                                  ║
║  1. SUPERSCRIPTION  → Date, Patient name, age, sex, address,    ║
║                        IP/OP number                              ║
║                                                                  ║
║  2. INSCRIPTION     → Name of drug (generic/brand)              ║
║                        Dose, strength, dosage form               ║
║                                                                  ║
║  3. SUBSCRIPTION    → Directions to pharmacist                   ║
║                        (dispense X tablets/ml)                   ║
║                                                                  ║
║  4. SIGNA (Sig)     → Directions to patient                      ║
║                        (1 tab BD x 5 days after food)            ║
║                                                                  ║
║  5. DOCTOR'S SIG    → Signature, Reg. no., stamp                 ║
╚══════════════════════════════════════════════════════════════════╝

Sample Prescription (Microbiology context):

┌──────────────────────────────────────────────────────┐
│  Dr. A. Kumar, MBBS, MD                              │
│  Reg. No. MH-12345                                   │
│  OPD Room 4, Civil Hospital                          │
│  Date: 15/07/2026                                    │
│                                                      │
│  Patient: Ram, 30yr/M     IP No: 1234                │
│                                                      │
│  Rx                                                  │
│                                                      │
│  Tab. Doxycycline 100mg         #14                  │
│  1-0-1 x 7 days (after food)                         │
│  (For: Scrub Typhus)                                 │
│                                                      │
│  Cap. Azithromycin 500mg        #3                   │
│  1-0-0 x 3 days (with food)                          │
│                                                      │
│  Sig: Take with plenty of water                      │
│       Avoid sun exposure                             │
│       Review after 5 days                            │
│                                                      │
│              [Signature + Stamp]                     │
└──────────────────────────────────────────────────────┘

Applications (Microbiology context):

Legal aspects:

• Schedule H drugs: prescription mandatory
• Schedule X drugs: prescription in duplicate, records maintained 2 years
• Generic prescription mandated by MCI (write INN names)

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Q7. RICKETTSIAL INFECTIONS

Classification of Rickettsiae:

╔══════════════════════════════════════════════════════════════════╗
║              CLASSIFICATION OF RICKETTSIAE                       ║
║                                                                  ║
║  GENUS RICKETTSIA:                                               ║
║  ├── Typhus Group:                                               ║
║  │   ├── R. prowazekii    → Epidemic typhus (louse)             ║
║  │   └── R. typhi         → Endemic/murine typhus (flea)         ║
║  │                                                               ║
║  ├── Spotted Fever Group:                                        ║
║  │   ├── R. rickettsii    → RMSF (tick)                         ║
║  │   ├── R. conorii       → Boutonneuse fever (India)           ║
║  │   └── R. akari         → Rickettsialpox (mite)               ║
║  │                                                               ║
║  GENUS ORIENTIA:                                                 ║
║  └── O. tsutsugamushi     → SCRUB TYPHUS (mite/chigger)         ║
║                                                                  ║
║  GENUS COXIELLA:                                                 ║
║  └── C. burnetii          → Q fever (no arthropod transmission)  ║
╚══════════════════════════════════════════════════════════════════╝

Morphology (General):

• Small, pleomorphic, gram-negative coccobacilli
• Obligate intracellular parasites (cannot grow on artificial media)
• Stain: Giemsa, Machiavello, Castaneda (NOT gram stain reliably)
• Found in cytoplasm (Typhus group) or nucleus (Spotted fever group)

Scrub Typhus (most common in India - MUHS favourite):

• Chigger bites → organism enters skin → local eschar forms
• Spreads via lymphatics → bacteremia → endothelial cell invasion
• Perivascular inflammatory infiltrate

• Eschar (pathognomonic) - painless black ulcer at bite site
• Fever (high grade, remittent)
• Maculopapular rash (trunk → extremities, spares palms/soles)
• Lymphadenopathy
• Myalgia, headache

WEIL-FELIX REACTION TABLE (classic serological test):
╔═════════════════╦═══════╦═══════╦════════╗
║ Disease         ║ OX-19 ║ OX-2  ║ OX-K   ║
╠═════════════════╬═══════╬═══════╬════════╣
║ Epidemic typhus ║  +++  ║   +   ║   -    ║
║ Murine typhus   ║  +++  ║  ++   ║   -    ║
║ Scrub typhus    ║   -   ║   -   ║  +++   ║
║ RMSF            ║  ++   ║  +++  ║   -    ║
║ Q fever         ║   -   ║   -   ║   -    ║
╚═════════════════╩═══════╩═══════╩════════╝

Lab Diagnosis of Rickettsial infections:

1. Weil-Felix Reaction - Agglutination of Proteus strains (OX-19, OX-2, OX-K)
   • Titre ≥1:160 significant; 4-fold rise in paired sera diagnostic
   • Cheap, widely available (but low specificity)
2. IFA (Immunofluorescence Assay) - GOLD STANDARD
   • Most sensitive and specific
   • Type-specific antibodies detected
3. ELISA - IgM/IgG antibodies
4. PCR - from whole blood; highly specific; early diagnosis
5. Weil-Felix test interpretation (see table above)
6. Isolation: BSL-3 facility required (not routine)
7. Skin biopsy of eschar: IHC or PCR for O. tsutsugamushi

• Doxycycline 100mg BD x 7 days (DOC for all rickettsial infections)
• Chloramphenicol (alternative, especially in children)
• Azithromycin (safe in pregnancy)

---

Q8. IMMUNOPATHOGENESIS AND LAB DIAGNOSIS OF RHD (Rheumatic Heart Disease)

Causative Agent: Streptococcus pyogenes (Group A Streptococcus)

Immunopathogenesis:

╔═══════════════════════════════════════════════════════════════╗
║          IMMUNOPATHOGENESIS OF RHD                            ║
║                                                               ║
║  GAS PHARYNGITIS                                              ║
║       ↓ [M protein antigen + streptolysins]                   ║
║  IMMUNE RESPONSE triggered (2-4 weeks later)                  ║
║       ↓                                                       ║
║  Antibodies formed against:                                   ║
║  ├── Anti-M protein antibodies                                ║
║  ├── Anti-streptolysin O (ASO) antibodies                     ║
║  └── Anti-hyaluronidase, Anti-streptokinase                   ║
║       ↓                                                       ║
║  MOLECULAR MIMICRY:                                           ║
║  M protein epitopes = similar to:                             ║
║  ├── Cardiac MYOSIN (sarcolemma)                              ║
║  ├── Laminin (heart valve endothelium)                        ║
║  └── Cardiac tropomyosin                                      ║
║       ↓                                                       ║
║  Cross-reactive antibodies attack HEART TISSUE:               ║
║  ├── VALVES (mitral most common)                              ║
║  ├── Myocardium (Aschoff bodies - pathognomonic)              ║
║  └── Pericardium                                              ║
║       ↓                                                       ║
║  RHEUMATIC FEVER → Repeated attacks →                         ║
║  CHRONIC RHD (mitral stenosis, regurgitation)                 ║
╚═══════════════════════════════════════════════════════════════╝

• Only pharyngeal GAS → RHD (NOT skin infections)
• Rheumatogenic strains: M types 1, 3, 5, 6, 14, 18, 19, 24
• Aschoff bodies (pathognomonic): perivascular granulomas with Anitschkow cells

Lab Diagnosis of RHD:

• Culture on Blood agar → beta-hemolytic colonies
• Gram stain: gram +ve cocci in chains
• Catalase negative, PYR positive
• Bacitracin sensitivity (Zone ≥10mm = Group A)
• Lancefield grouping with anti-A antiserum

• Rapid Strep Test (Lateral flow) for GAS antigen from throat swab
• Sensitivity ~70-80%

• 200 Todd units in adults, >333 in children = significant

• 4-fold rise in paired sera (2-4 weeks apart) = recent infection

MAJOR CRITERIA:          MINOR CRITERIA:
• Carditis                • Fever
• Polyarthritis           • Prolonged PR interval (ECG)
• Chorea                  • Elevated ESR/CRP
• Erythema marginatum     • Leucocytosis
• Subcutaneous nodules    • Previous RF/RHD

Diagnosis: 2 Major OR 1 Major + 2 Minor 
           + Evidence of preceding GAS infection (ASO/culture)

• Acute: Benzathine Penicillin G 1.2 MU IM single dose
• Secondary prophylaxis: Benzathine Penicillin G 1.2 MU IM every 3 weeks for minimum 5 years / up to age 21

---

Q9. LABORATORY DIAGNOSIS OF LEPTOSPIROSIS

Clinical Phases:

• Phase 1 (Leptospiremic): Days 1-7, fever, headache, myalgia (bacteria in blood and CSF)
• Phase 2 (Immune): Days 7-14, antibody production, bacteria clear from blood; Weil's disease (jaundice, renal failure, hemorrhage)

DIAGRAM - Lab Diagnosis Strategy by Phase:

╔══════════════════════════════════════════════════════════════╗
║        LAB DIAGNOSIS OF LEPTOSPIROSIS                        ║
║                                                              ║
║  WEEK 1 (leptospiremic phase):                               ║
║  ├── Blood culture (EMJH medium or Fletcher's medium)        ║
║  ├── CSF culture (if meningitic)                             ║
║  ├── Urine (from day 7 onwards)                              ║
║  ├── PCR (blood/urine) - most sensitive, early               ║
║  └── Dark-field microscopy (blood - not reliable)            ║
║                                                              ║
║  WEEK 2 onwards (immune phase):                              ║
║  ├── SEROLOGY (antibodies appear)                            ║
║  │   ├── MAT (Microscopic Agglutination Test) - GOLD STANDARD║
║  │   ├── IgM ELISA (Panbio, Leptocheck - rapid)             ║
║  │   └── Macroscopic slide agglutination test (screening)    ║
║  └── Urine culture (organisms shed in urine)                 ║
╚══════════════════════════════════════════════════════════════╝

Detailed Lab Methods:

• Blood (early), urine (late)
• Thin, motile coiled organisms with hooked ends seen
• Low sensitivity; false positives common (fibrin threads confused)

• EMJH (Ellinghausen-McCullough-Johnson-Harris) medium or Fletcher's semi-solid medium
• Incubate at 28-30°C for 6-8 weeks (slow growing)
• Positive in 50-70% early cases

• Blood in first week; urine from day 7
• Highly sensitive and specific; used in India increasingly

• GOLD STANDARD for serology
• Uses live or formalin-killed Leptospira antigens + patient serum
• Titre ≥1:100 in single sample suggestive
• 4-fold rise in paired sera (2 weeks apart) = diagnostic
• Can identify specific serovar (important epidemiologically)

• Detects IgM antibodies from day 5-7
• Commercially available kits (Panbio Leptospira IgM ELISA)
• Sensitivity ~90%, Specificity ~95%

• Screening test; uses killed antigens; simple
• Titre ≥1:40 = significant

Leptospira - "?"  shaped / hooked ends
  ├── Thin, tightly coiled
  ├── 6-20 μm long
  ├── Stain: Silver impregnation (Fontana's stain), Giemsa
  └── Dark field: glistening, rapidly rotating

---

Q10. NACO STRATEGIES FOR HIV

Major Strategies under NACP (National AIDS Control Programme):

╔══════════════════════════════════════════════════════════════╗
║            NACO STRATEGIES FOR HIV                           ║
║                                                              ║
║  1. PREVENTION STRATEGIES                                    ║
║  ├── IEC (Information, Education, Communication)            ║
║  ├── BCC (Behaviour Change Communication)                    ║
║  ├── Condom promotion (NACO provides free condoms)           ║
║  ├── STI management (treat STIs → reduce HIV risk)           ║
║  ├── ICTC (Integrated Counselling & Testing Centres)         ║
║  ├── Blood Safety (mandatory HIV screening of all blood)     ║
║  ├── Harm Reduction for IDUs (needle exchange, OST)          ║
║  └── PMTCT (Prevention of Mother to Child Transmission)      ║
║                                                              ║
║  2. CARE, SUPPORT & TREATMENT                                ║
║  ├── ART Centres (Free ART under NACP IV)                   ║
║  ├── CD4 & Viral Load monitoring                             ║
║  ├── OI (Opportunistic Infection) management                 ║
║  └── Nutritional support                                     ║
║                                                              ║
║  3. TARGETED INTERVENTIONS (TI)                              ║
║  ├── FSW (Female Sex Workers)                                ║
║  ├── MSM (Men having Sex with Men)                           ║
║  ├── IDU (Injecting Drug Users)                              ║
║  └── Transgender community                                   ║
║                                                              ║
║  4. RESEARCH & SURVEILLANCE                                  ║
║  ├── ANC sentinel surveillance                               ║
║  ├── IBBS (Integrated Biological Behavioural Surveillance)   ║
║  └── HIV estimations (UNAIDS methodology)                    ║
╚══════════════════════════════════════════════════════════════╝

Key NACO Programmes:

• ALL HIV-positive individuals started on ART regardless of CD4 count
• First-line: TDF + 3TC (or FTC) + EFV (TLE regimen)
• Pediatric: ABC + 3TC + EFV

---

Q11. HIV - LAB DIAGNOSIS

Classification of Tests:

╔════════════════════════════════════════════════════════════════╗
║              HIV LAB DIAGNOSIS ALGORITHM                       ║
║                                                                ║
║  SCREENING TESTS (Sensitive):                                  ║
║  ├── ELISA (4th generation: detects Ag+Ab)                    ║
║  ├── Rapid immunochromatography tests                          ║
║  └── Chemiluminescent immunoassay (CLIA)                       ║
║                                                                ║
║  CONFIRMATORY TEST:                                            ║
║  └── Western Blot (detects specific band pattern)              ║
║                                                                ║
║  SUPPLEMENTAL/ADVANCED:                                        ║
║  ├── HIV RNA PCR (Viral Load) - quantitative                   ║
║  ├── HIV DNA PCR - for infants <18 months                      ║
║  ├── p24 Antigen assay                                         ║
║  └── CD4 count - monitoring, not diagnosis                     ║
╚════════════════════════════════════════════════════════════════╝

NACO Testing Strategy (Rapid Tests - India):

NACO ALGORITHM:
Patient comes for HIV testing
        ↓
   Test A (ELISA/Rapid)
        ↓
  Non-reactive → HIV NEGATIVE
  Reactive ↓
   Test B (different antigen/format)
        ↓
  Non-reactive → Discordant → Test C → report
  Reactive ↓
   Test C (third test)
        ↓
  Reactive → HIV POSITIVE
  Non-reactive → INDETERMINATE → repeat in 2-4 weeks

Detail of Individual Tests:

• Detects both p24 antigen AND anti-HIV antibodies
• Window period: 11-15 days (4th gen) vs 22-25 days (3rd gen)
• Very high sensitivity (>99.5%)
• False positives in: malaria, pregnancy, autoimmune disease

• Detects antibodies to specific HIV proteins
• POSITIVE: bands at p24 + gp41 + gp120/160 (CDC criteria: ≥2 bands from p24, gp41, gp120/160)
• Highest specificity

• Detects HIV RNA copies/mL blood
• Used for: early diagnosis (acute HIV), monitoring ART response, diagnosis in infants
• Undetectable VL (<20-50 copies/mL) = treatment success

• Normal: 500-1500 cells/μL
• <500: Start ART (India: all cases)
• <200: AIDS-defining; start OI prophylaxis (Cotrimoxazole)
• <50: Very high risk for CMV, MAC

• Appears before antibodies (11-14 days post infection)
• Used in 4th gen combo assays

• Two positive tests on the same day with different antigens = HIV positive

---

Q12. CRYPTOSPORIDIUM - Note / HIV with watery diarrhea + sporulated oocysts

• Phylum: Apicomplexa (Sporozoa)
• Class: Coccidia
• Intracellular parasite of intestinal epithelium

Morphology:

• Oocysts: 4-5 μm (small, spherical), contain 4 sporozoites
• Thick-walled oocysts: shed in stool (environmental transmission)
• Thin-walled oocysts: auto-infection (rupture within gut)

Life Cycle:

╔══════════════════════════════════════════════════════════════╗
║         LIFE CYCLE OF CRYPTOSPORIDIUM                        ║
║                                                              ║
║  THICK-WALLED OOCYSTS (infective form)                       ║
║       ↓ [ingested in contaminated water/food]                ║
║  EXCYSTATION in small intestine                              ║
║       ↓                                                      ║
║  4 SPOROZOITES released → attach to brush border             ║
║       ↓                                                      ║
║  MEROGONY (asexual):                                         ║
║  Type I meronts → 8 merozoites → new Type I (cycle)          ║
║  Type II meronts → 4 merozoites → SEXUAL phase               ║
║       ↓                                                      ║
║  GAMETOGONY (sexual):                                        ║
║  Microgamont (male) + Macrogamont (female) → ZYGOTE          ║
║       ↓                                                      ║
║  OOCYSTS formed:                                             ║
║  ├── THICK-WALLED → shed in stool (80%)                      ║
║  └── THIN-WALLED → autoinfection (20%)                       ║
╚══════════════════════════════════════════════════════════════╝

Clinical Features:

• Immunocompetent: Mild, self-limiting watery diarrhea (1-2 weeks)
• AIDS (CD4 <200): Profuse, cholera-like watery diarrhea (3-20 L/day), wasting, prolonged, may be fatal
• Associated with: biliary cryptosporidiosis, pulmonary involvement in AIDS

Lab Diagnosis:

• Oocysts stain pink/red against blue background
• Size: 4-5 μm
• PARUL mnemonic: Pink oocysts on Acid-fast stain, Round, Under Light microscope

DIAGRAM - Modified ZN Stain:
╔══════════════════════════════════════╗
║  Blue background (counterstain)      ║
║                                      ║
║    ●  ●  ●  ← PINK oocysts (4-5μm) ║
║  ●    ●    ●  (sporulated)          ║
║    ●  ●  ●                           ║
║                                      ║
║  = Cryptosporidium oocysts           ║
╚══════════════════════════════════════╝

• Best sensitivity for oocyst detection
• Uses fluorescently labelled monoclonal antibodies

• Highly sensitive and specific

• Organisms at brush border (apex of villi)
• PAS stain: purple dots at luminal surface

• Immunocompetent: Supportive (self-limiting)
• AIDS patients: Nitazoxanide 500mg BD x 3 days + ART (ART is most important - restores immunity)
• Paromomycin + Azithromycin (adjunct)

---

Q13. NOTE ON LYMPHATIC FILARIASIS

Morphology of Microfilariae:

╔══════════════════════════════════════════════════════════╗
║          W. bancrofti vs B. malayi - MICROFILARIAE       ║
║                                                          ║
║  W. bancrofti:                  B. malayi:               ║
║  • Sheath present               • Sheath present         ║
║  • NO nuclei in tail tip        • 2 nuclei in tail tip   ║
║  • Sheath does NOT stain        • Sheath stains PINK     ║
║    with Giemsa                    with Giemsa            ║
║  • Body nuclei: not reach tip   • Subterminal space      ║
║                                                          ║
║  PERIODICITY:                                            ║
║  • Nocturnal periodicity (appear in blood at night)      ║
║  • Except: Pacific strain (W. bancrofti) - diurnal       ║
╚══════════════════════════════════════════════════════════╝

Life Cycle:

╔════════════════════════════════════════════════════════════╗
║          LIFE CYCLE OF W. BANCROFTI                        ║
║                                                            ║
║  MOSQUITO (Culex):                                         ║
║  Ingests microfilariae with blood meal                     ║
║       ↓                                                    ║
║  Mf develop in flight muscle:                              ║
║  L1 → L2 → L3 (infective larva - filariform)               ║
║       ↓ migrate to proboscis                               ║
║  L3 deposited on skin during blood meal                    ║
║       ↓ enters through bite wound                          ║
║  HUMAN HOST:                                               ║
║  L3 → lymphatics → L4 → ADULT WORMS                       ║
║  (Male + Female mate in lymph nodes)                       ║
║       ↓                                                    ║
║  Females release microfilariae → bloodstream               ║
║       ↓ (Nocturnal periodicity: appear at night)           ║
║  Microfilariae in peripheral blood                         ║
║  (taken up by mosquito to continue cycle)                  ║
╚════════════════════════════════════════════════════════════╝

Pathogenesis:

• Dead worms → lymphangitis, lymphadenitis
• Repeated episodes → fibrosis, obstruction of lymphatics
• Lymphedema → chronic → Elephantiasis (limbs, scrotum/hydrocele, vulva)
• Tropical Pulmonary Eosinophilia (TPE): Aberrant immune response → Mf trapped in lungs → eosinophilia >3000/μL, cough, wheeze

Lab Diagnosis:

• Collect blood at NIGHT (11pm-1am) for nocturnal periodicity
• Thick film: Giemsa stain
• Look for microfilariae (sheathed)

• Knott's technique: 1ml blood + 9ml 2% formalin → centrifuge → sediment examined
• Membrane filtration (Nuclepore): blood filtered through 3μm pore filter

• Detects W. bancrofti circulating filarial antigen (CFA)
• ICT Filariasis test (BinaxNOW)
• Can be done at any time (not limited to night)
• Sensitivity >95%; blood collected anytime

• ELISA for IgG4 (anti-filarial antibodies)
• Less specific due to cross-reactions

• "Filarial dance sign" - live moving adult worms in scrotal/lymph node ultrasound

• DEC (Diethylcarbamazine citrate) 6mg/kg/day x 12 days (kills microfilariae + some adult worms)
• Ivermectin + Albendazole (MDA - Mass Drug Administration programme, India)
• Doxycycline: kills Wolbachia (endosymbiont of filariae) → kills adult worms

---

Q14. BASIC LAB DIAGNOSIS OF FUNGAL INFECTIONS

Specimens by site:

• Skin: Skin scrapings (from active edge of lesion)
• Hair: Infected hair shaft + kerion
• Nails: Nail clippings
• Deep infections: BAL, sputum, CSF, tissue biopsy, blood

DIAGRAM - Overview of Fungal Lab Diagnosis:

╔══════════════════════════════════════════════════════════════╗
║         FUNGAL LAB DIAGNOSIS OVERVIEW                        ║
║                                                              ║
║  1. DIRECT MICROSCOPY                                        ║
║  ├── KOH Mount (10-20% KOH) - GOLD STANDARD for superficial  ║
║  │   Dissolves keratin → reveals fungal elements             ║
║  │   See: hyphae, spores, pseudohyphae                       ║
║  ├── India Ink Preparation (Cryptococcus neoformans)         ║
║  │   Capsule appears as clear halo around yeast              ║
║  ├── Gram stain: Candida (gram +ve pseudohyphae)             ║
║  ├── ZN stain: Not useful                                    ║
║  └── Calcofluor white stain (fluorescence) - most sensitive  ║
║                                                              ║
║  2. CULTURE                                                  ║
║  ├── SDA (Sabouraud's Dextrose Agar) - BASIC MEDIUM          ║
║  │   pH 5.6, temp 22-28°C, chloramphenicol added            ║
║  │   Inhibits bacteria                                       ║
║  ├── Dermatophyte Test Medium (DTM) - dermatophytes          ║
║  ├── CHROMagar Candida - Candida speciation by color         ║
║  └── BHI agar - systemic/dimorphic fungi                     ║
║                                                              ║
║  3. BIOCHEMICAL/IDENTIFICATION                               ║
║  ├── Germ tube test (Candida albicans)                       ║
║  ├── Sugar fermentation/assimilation tests                   ║
║  └── MALDI-TOF (modern rapid ID)                             ║
║                                                              ║
║  4. SEROLOGY/ANTIGEN DETECTION                               ║
║  ├── Cryptococcal antigen (LA/ELISA) - CrAg                  ║
║  ├── Galactomannan (Aspergillus antigen) - ELISA             ║
║  ├── Beta-D-glucan (panfungal marker)                        ║
║  └── Histoplasma antigen (urine/serum)                       ║
║                                                              ║
║  5. MOLECULAR/PCR                                            ║
║  └── Panfungal PCR, species-specific PCR                     ║
╚══════════════════════════════════════════════════════════════╝

Key Stains Summary:

Germ Tube Test (for C. albicans):

• Incubate Candida in human serum at 37°C for 2-3 hours
• True germ tube (no constriction at origin) = C. albicans positive
• Distinguishes C. albicans from other Candida species

---

Q15. NOTE ON HISTOPLASMOSIS

• Thermally dimorphic fungus
• Mold at 25°C (in environment), Yeast at 37°C (in tissue)

Epidemiology:

• Found in soil rich in bird/bat droppings (caves, chicken coops)
• Endemic: Ohio and Mississippi River valleys (USA), India (rare but reported)
• Inhalation of microconidia = mode of infection
• High-risk groups: cave explorers (spelunkers), demolition workers, farmers

Morphology:

╔══════════════════════════════════════════════════════╗
║        HISTOPLASMA CAPSULATUM - MORPHOLOGY           ║
║                                                      ║
║  IN ENVIRONMENT (25°C) - MOLD PHASE:                 ║
║  ├── Septate hyphae                                  ║
║  ├── Tuberculate macroconidia (diagnostic)           ║
║  │   [large, thick-walled, spiky/spiked surface]     ║
║  └── Microconidia (2-4μm, smooth) - INFECTIVE        ║
║                                                      ║
║  IN TISSUE (37°C) - YEAST PHASE:                     ║
║  ├── Small oval yeast cells (2-4 μm)                 ║
║  ├── INTRACELLULAR in macrophages                    ║
║  ├── Narrow-based budding                            ║
║  └── "Ring of haze" around each yeast (not capsule)  ║
╚══════════════════════════════════════════════════════╝

Clinical Forms:

Lab Diagnosis:

1. Direct microscopy (Giemsa/PAS): Intracellular oval yeasts in macrophages in BAL, bone marrow, peripheral blood buffy coat
2. Culture (SDA/BHI): 25°C → mold with tuberculate macroconidia; 37°C → yeast (takes 2-6 weeks; BSL-3)
3. Histoplasma antigen detection (ELISA): Urine/serum; most useful in disseminated disease; sensitivity >90% in AIDS
4. Complement Fixation (CF) + Immunodiffusion (ID): M and H precipitin bands; H band = active infection
5. PCR: Rapid, sensitive
6. Skin test (Histoplasmin): Epidemiological tool only (not diagnostic)

• Mild: Itraconazole 200mg BD x 3-12 months
• Severe/Disseminated: Liposomal Amphotericin B → then Itraconazole
• AIDS: lifelong secondary prophylaxis with Itraconazole

---

Q16. CAUSATIVE AGENT OF SCRUB TYPHUS AND LAB DIAGNOSIS

• Vector: Larval trombiculid mite (chigger) - Leptotrombidium deliense
• Reservoir: Wild rodents (rats, mice); mites are also reservoir (transovarial transmission)
• Mode of transmission: Bite of infected chigger larva

Morphology:

• Obligate intracellular gram-negative coccobacillus
• Found in cytoplasm AND nucleus of host cells
• Cannot be cultured on routine bacteriological media

Clinical Features:

• Eschar (black ulcer at bite site - pathognomonic) - present in 50-80% cases
• Fever, headache, myalgia
• Generalized lymphadenopathy (including eschar-draining node)
• Maculopapular rash (trunk → periphery)
• Complications: meningoencephalitis, ARDS, myocarditis, renal failure

Lab Diagnosis:

SPECIMEN: Blood (EDTA - for PCR, culture); Eschar biopsy

╔═══════════════════════════════════════════════════════════╗
║         LAB DIAGNOSIS OF SCRUB TYPHUS                     ║
║                                                           ║
║  1. WEIL-FELIX REACTION (Traditional, cheap):             ║
║     OX-K agglutination positive (titre ≥1:80 significant) ║
║     OX-19 and OX-2 = NEGATIVE                             ║
║     (Cross-reaction with Proteus OX-K antigen)            ║
║                                                           ║
║  2. IFA (Gold standard):                                  ║
║     Anti-O. tsutsugamushi IgM/IgG antibodies              ║
║     Titre ≥1:50 = positive; 4-fold rise = diagnostic      ║
║                                                           ║
║  3. PCR (Early, best test):                               ║
║     Real-time PCR from blood/eschar biopsy                ║
║     Detects 47kDa gene of Orientia                        ║
║     Most sensitive in first week                          ║
║                                                           ║
║  4. Eschar biopsy:                                        ║
║     IHC (immunohistochemistry) or PCR                     ║
║     Confirms organism in tissue                           ║
║                                                           ║
║  5. ELISA (IgM):                                          ║
║     Positive from day 7-10                                ║
║     Commercially available kits                           ║
║                                                           ║
║  6. Isolation:                                            ║
║     Mouse inoculation / cell culture (L-929 cells)        ║
║     BSL-3 - not routine                                   ║
╚═══════════════════════════════════════════════════════════╝

• Doxycycline 100mg BD x 7 days (DOC)
• Alternatives: Azithromycin (safe in pregnancy), Chloramphenicol
• Rapid response to Doxycycline is itself a therapeutic test (defervescence within 24-48 hrs)

---

Q17. PUO (Pyrexia of Unknown Origin)

• Fever >38.3°C (101°F)
• Duration >3 weeks
• No diagnosis after 1 week of in-hospital investigation

Classification:

Causes (Classic Triad: 30-30-20-10-10):

• Infections: 30% (TB most common in India, SBE, abscess)
• Neoplasms: 30% (Lymphoma, leukemia, solid tumors)
• Collagen vascular diseases: 20% (SLE, RA, Vasculitis)
• Miscellaneous: 10% (Drug fever, Factitious fever)
• Undiagnosed: 10%

Microbiological Lab Workup:

STEP-BY-STEP APPROACH:
┌──────────────────────────────────────────────────────────┐
│ BASIC (all cases):                                       │
│ • CBC with differential (eosinophilia? leukocytosis?)   │
│ • Blood cultures x 3 (aerobic + anaerobic, 12 hrs apart)│
│ • Urine culture                                          │
│ • ESR, CRP, Procalcitonin                               │
│ • Widal test (if Salmonella suspected)                   │
│ • Weil-Felix (Rickettsial infections)                    │
│ • Malaria MP/RDT                                         │
│                                                          │
│ DIRECTED (based on clinical clues):                      │
│ • Mantoux + Sputum AFB/CBNAAT (TB)                      │
│ • ANA, anti-dsDNA (SLE)                                  │
│ • ECHO (SBE/endocarditis)                                │
│ • Bone marrow exam (Leishmania, Typhoid, Malaria)        │
│ • Serology: Leptospira IgM, Brucella, Dengue NS1        │
│ • CT chest/abdomen (lymphoma, abscess)                   │
│ • PET-CT scan (occult malignancy/infection)              │
│ • Tissue biopsy (LN, liver, bone marrow)                 │
└──────────────────────────────────────────────────────────┘

---

Q18. INDICATIONS OF BLOOD CULTURE - COLLECTION AND PROCESSING

Indications for Blood Culture:

1. Suspected bacteremia/septicemia (fever >38.5°C with rigors)
2. Endocarditis (suspected SBE - 3 sets mandatory)
3. PUO (pyrexia of unknown origin)
4. Typhoid fever (best yield in first week)
5. Meningitis (blood culture + CSF culture together)
6. Neonatal sepsis
7. Immunocompromised patients with fever
8. Post-operative fever (>48 hrs after surgery)
9. Catheter-related bloodstream infection (CRBSI)

Collection of Blood for Culture:

╔══════════════════════════════════════════════════════════════╗
║          BLOOD CULTURE COLLECTION PROTOCOL                   ║
║                                                              ║
║  TIMING: Collect at PEAK OF FEVER (during rigor/chill)       ║
║          OR before antibiotic administration                  ║
║                                                              ║
║  SITE: Peripheral vein (antecubital fossa)                   ║
║        NOT from existing IV line (contamination risk)        ║
║                                                              ║
║  VOLUME:                                                      ║
║  Adults: 10 mL per bottle (5 mL aerobic + 5 mL anaerobic)   ║
║  Children: 1-5 mL                                            ║
║  Neonates: 0.5-1 mL                                          ║
║                                                              ║
║  NUMBER OF SETS: Minimum 2 sets (from 2 different sites)     ║
║                  SBE: 3 sets in 24 hours                     ║
║                                                              ║
║  BLOOD:BROTH RATIO: 1:10 (dilutes inhibitors like Ab)        ║
║                                                              ║
║  ASEPTIC TECHNIQUE:                                          ║
║  1. Clean skin with 70% alcohol → dry                        ║
║  2. Apply 2% chlorhexidine or povidone-iodine                ║
║  3. Allow to dry 30 seconds                                  ║
║  4. Venepuncture with sterile needle                         ║
║  5. Change needle before inoculating bottle                  ║
╚══════════════════════════════════════════════════════════════╝

Processing of Blood Culture:

1. Inoculate BHI (Brain Heart Infusion) broth / Tryptic Soy Broth
2. Incubate at 37°C, inspect daily for 7 days for turbidity, gas, hemolysis
3. Blind subculture at 24hrs, 48hrs, 7 days on blood agar + MacConkey

• Continuously monitor CO2 production (by-product of bacterial metabolism)
• Alert when positive (usually within 12-24 hrs for common organisms)
• Sensitivity >97%
• Flagged positives → Gram stain → Subculture → ID + Sensitivity

• Gram stain of positive bottle
• Subculture on appropriate media
• Species identification (MALDI-TOF or conventional biochemicals)
• Antimicrobial susceptibility testing (Kirby-Bauer or MIC by broth dilution)

---

Q19. DIFFERENCE BETWEEN PRIMARY AND SECONDARY IMMUNE RESPONSE

╔════════════════════════════════════════════════════════════════════╗
║        PRIMARY vs SECONDARY IMMUNE RESPONSE                        ║
╠═════════════════════════╦═══════════════════╦══════════════════════╣
║ Feature                 ║ PRIMARY           ║ SECONDARY            ║
╠═════════════════════════╬═══════════════════╬══════════════════════╣
║ Trigger                 ║ First exposure    ║ Re-exposure (booster)║
║ Lag phase               ║ 5-10 days         ║ 1-3 days             ║
║ Magnitude (Ab titre)    ║ Low               ║ Much HIGHER          ║
║ Duration                ║ Shorter           ║ Longer               ║
║ Antibody class          ║ IgM first → IgG   ║ Mainly IgG           ║
║ Affinity                ║ Lower             ║ HIGHER (affinity     ║
║                         ║                   ║ maturation)          ║
║ Cells involved          ║ Naive B + T cells  ║ Memory B + T cells   ║
║ Memory cells formed     ║ YES (first time)   ║ YES (expanded)       ║
╚═════════════════════════╩═══════════════════╩══════════════════════╝

DIAGRAM:

Ab
Titre    │                              ╭─────────── (Secondary)
(log)    │                             /  MUCH HIGHER
         │                            /
         │              ╭────────────/
         │             /  (Primary)
         │            /
         │───────────/
         │(lag)
         └──────────────────────────────────────────
              1st Ag         2nd Ag (re-exposure)
              exposure
         ← 5-10 day lag →  ← 1-3 day lag →

Basis of Secondary Response (MEMORY CELLS):

• After primary exposure: long-lived Memory B cells and Memory T cells formed
• Memory cells persist for years to decades
• On re-exposure → rapid clonal expansion → fast, high-magnitude, high-affinity Ab response

Applications (Examples):

---

Q20. LIFE CYCLE AND LAB DIAGNOSIS OF TAENIA SOLIUM

1. Taeniasis (intestinal): adult tapeworm in intestine (man = definitive host)
2. Cysticercosis (tissue): larval cysts (man = accidental intermediate host) - MORE DANGEROUS

Life Cycle:

╔══════════════════════════════════════════════════════════════════╗
║            LIFE CYCLE OF TAENIA SOLIUM                           ║
║                                                                  ║
║  DEFINITIVE HOST: Human                                          ║
║  NORMAL INTERMEDIATE HOST: Pig                                   ║
║  ACCIDENTAL INTERMEDIATE HOST: Human (cysticercosis)             ║
║                                                                  ║
║  ┌─── NORMAL CYCLE ──────────────────────────────────────┐       ║
║  │                                                        │       ║
║  │  ADULT WORM in human small intestine                  │       ║
║  │       ↓ gravid proglottids shed in stool              │       ║
║  │  EGGS in environment                                  │       ║
║  │       ↓ PIG ingests eggs from contaminated soil       │       ║
║  │  ONCOSPHERE hatches in pig gut                        │       ║
║  │       ↓ penetrates gut wall → blood → muscles         │       ║
║  │  CYSTICERCUS CELLULOSAE in pig muscle (pork)          │       ║
║  │       ↓ human eats undercooked infected pork          │       ║
║  │  SCOLEX evaginates in human intestine                 │       ║
║  │       ↓ attaches to mucosa                            │       ║
║  │  ADULT WORM (2-7m long) develops                      │       ║
║  └────────────────────────────────────────────────────────┘       ║
║                                                                  ║
║  ┌─── CYSTICERCOSIS CYCLE (DANGEROUS) ──────────────────┐       ║
║  │  Human ingests EGGS (from contaminated food/water,   │       ║
║  │  or autoinfection - gravid proglottids regurgitate)  │       ║
║  │       ↓ Oncospheres hatch                            │       ║
║  │  Penetrate gut → bloodstream → TISSUES               │       ║
║  │  ├── BRAIN → Neurocysticercosis (NCC) - COMMONEST    │       ║
║  │  ├── Eye, muscles, heart, skin                       │       ║
║  │  └── Cysticercus cellulosae forms (fluid-filled cyst)│       ║
║  └──────────────────────────────────────────────────────┘       ║
╚══════════════════════════════════════════════════════════════════╝

Morphology of Adult Worm:

SCOLEX (head):
┌────────────────────────────────────┐
│  4 SUCKERS (acetabula)             │
│  ROSTELLUM with double row of HOOKS│ ← Armed (distinguishes from T. saginata)
│  (T. saginata has NO hooks)        │
└────────────────────────────────────┘
NECK → PROGLOTTIDS
├── Immature proglottids
├── Mature proglottids (5-10: uterine branches per side)
└── Gravid proglottids (7-13 uterine branches per side)
    T. saginata has 15-30 branches

Lab Diagnosis:

1. Stool examination:
   • Wet preparation or concentration (ZnSO4 floatation / formol-ether)
   • Find: Eggs - round/oval, 30-40μm, thick brown striated shell, 6-hooked oncosphere inside
   • Eggs of T. solium and T. saginata are morphologically IDENTICAL
   • Find: Gravid proglottids - count uterine branches (<13 = T. solium; >15 = T. saginata)
2. Scolex examination: After treatment (praziquantel/niclosamide) - identify by presence/absence of hooks
3. Perianal swab (Graham's test): Less useful than for Enterobius, but proglottids may be detected

1. Neuroimaging (CT/MRI brain):
   • MRI: Fluid-filled cysts with eccentric scolex (hypodense lesion + bright scolex = "hole with a dot" sign)
   • CT: Calcified cysts (dead worms), perilesional edema
2. Serology:
   • ELISA (IgG anti-cysticercal antibodies) - sensitivity 75-95% in NCC
   • EITB (Enzyme-linked immunoelectrotransfer blot) - most specific
3. CSF examination (NCC with meningitis):
   • Eosinophilic pleocytosis, elevated protein
   • CSF ELISA positive
4. Subcutaneous nodule biopsy:
   • Cysticercus cellulosae identified histologically
   • Bladder-like structure with invaginated scolex and 4 suckers
5. PCR: Highly sensitive for CSF/blood

• Taeniasis: Praziquantel 10mg/kg single dose OR Niclosamide
• NCC: Albendazole 15mg/kg/day x 8-28 days (+ Dexamethasone for edema)
• Calcified cysts: No antiparasitic needed; manage seizures with anticonvulsants

---

Q21. 15-year-old male, fever not responding to antibiotics, chills for 4 days, anemia, splenomegaly, CRESCENTS on smear

---

Etiological Agent: Plasmodium falciparum

Classification:

Life Cycle:

╔══════════════════════════════════════════════════════════════════╗
║         LIFE CYCLE OF PLASMODIUM (Two-host cycle)                ║
║                                                                  ║
║  ANOPHELES MOSQUITO (definitive host - sexual cycle):            ║
║  ├── Ingests gametocytes from infected human                     ║
║  ├── Microgamete + Macrogamete → ZYGOTE → OOKINETE               ║
║  ├── Ookinete → OOCYST in stomach wall                           ║
║  └── SPOROZOITES released → migrate to salivary glands           ║
║                                                                  ║
║  HUMAN (intermediate host - asexual cycle):                      ║
║  ├── SPOROZOITES injected with mosquito bite                     ║
║  │                                                               ║
║  ├── EXOERYTHROCYTIC (Pre-erythrocytic) cycle in LIVER:          ║
║  │   Sporozoites → hepatocytes → LIVER SCHIZONTS                 ║
║  │   → 10,000 MEROZOITES / liver cell                            ║
║  │   P. vivax/ovale: HYPNOZOITES (dormant, relapse)              ║
║  │                                                               ║
║  └── ERYTHROCYTIC cycle in RBCs:                                 ║
║      Merozoites → invade RBCs                                    ║
║      RING STAGE → TROPHOZOITE → ERYTHROCYTIC SCHIZONT            ║
║      → MEROZOITES (rupture RBC → fever/chills)                   ║
║      → Some → GAMETOCYTES (P. falciparum = CRESCENTS)            ║
╚══════════════════════════════════════════════════════════════════╝

P. falciparum - Specific features:

• Ring stage: Multiple rings per RBC (polyinfection), Maurer's clefts in cytoplasm
• Infected RBCs: NOT enlarged (unlike P. vivax); show knobs (cytoadherence)
• Sequestration: infected RBCs stick to capillary endothelium (PfEMP1 protein) → cerebral malaria
• No schizont/trophozoite in peripheral blood (sequestered in deep microvasculature)
• Only rings + crescents visible in peripheral smear

Lab Diagnosis:

╔══════════════════════════════════════════════════════════════╗
║         LAB DIAGNOSIS OF MALARIA                             ║
║                                                              ║
║  1. PERIPHERAL BLOOD SMEAR (GOLD STANDARD)                   ║
║  ├── Thick film (screening): more concentrated, better for   ║
║  │   detecting parasites at low parasitemia                  ║
║  ├── Thin film (species ID): morphology of ring, RBC size    ║
║  └── Stain: Leishman, Giemsa, Wright's stain                 ║
║                                                              ║
║  COLLECT: During fever/before antipyretics                   ║
║           (during erythrocytic rupture - max parasitemia)    ║
║                                                              ║
║  2. RAPID DIAGNOSTIC TEST (RDT / ICT)                        ║
║  ├── Detects HRP-2 antigen (P. falciparum specific)          ║
║  ├── pLDH (pan-malarial antigen, all species)                ║
║  ├── Aldolase (pan-malarial)                                 ║
║  └── SD Bioline Malaria, Paracheck (India)                   ║
║  • Sensitivity: >95% for P. falciparum                       ║
║  • Results in 15-20 minutes                                  ║
║                                                              ║
║  3. QBC (Quantitative Buffy Coat)                            ║
║  ├── Capillary tube centrifugation                           ║
║  ├── Acridine orange stain (fluorescent)                     ║
║  └── Fluorescent parasites visible at buffy coat             ║
║                                                              ║
║  4. PCR (Molecular)                                          ║
║  ├── Most sensitive (detects <5 parasites/μL)                ║
║  ├── Species-specific                                        ║
║  └── Used when smear negative, low parasitemia               ║
║                                                              ║
║  5. SEROLOGY (IFAT, ELISA)                                   ║
║  └── Epidemiological surveys, NOT for acute diagnosis         ║
╚══════════════════════════════════════════════════════════════╝

P. falciparum smear features (easy to draw):

THIN FILM - P. falciparum:
╔══════════════════════════════════════════════════════╗
║  RBC NOT ENLARGED                                    ║
║                                                      ║
║  ┌────────┐     ┌────────┐    ┌────────┐             ║
║  │ ○  ○  │     │  ○○    │    │CRESCENT│             ║
║  │(double │     │(double │    │ ))))   │             ║
║  │ ring)  │     │ infect)│    │GAMETOC.│             ║
║  └────────┘     └────────┘    └────────┘             ║
║  Ring stage  Polyinfection   Banana-shaped           ║
║                               gametocyte             ║
╚══════════════════════════════════════════════════════╝

Treatment (NVBDCP India Guidelines):

• Artemisinin Combination Therapy (ACT): Artemether-Lumefantrine (AL) OR Artesunate + Sulfadoxine-Pyrimethamine (AS+SP)
• Duration: 3 days
• Add Primaquine 0.75 mg/kg single dose (gametocidal - prevents transmission)

• Artesunate IV/IM (DOC) 2.4 mg/kg at 0, 12, 24 hrs then once daily
• Alternatives: Quinine IV
• Supportive: IV fluids, blood transfusion, anticonvulsants, ICU

• Chloroquine (3 days) + Primaquine 0.25 mg/kg/day x 14 days
• Check G6PD before Primaquine (causes hemolysis in G6PD deficiency)

---

References: Apurba Shastri's Textbook of Microbiology (as per MUHS); Jawetz, Melnick & Adelberg's Medical Microbiology 28th Ed; Murray's Medical Microbiology 9th Ed; NACO/NVBDCP India Guidelines.

MUHS Exam tip - MUHS 2 marks = Define + 1-2 key points. 3 marks = Diagram + brief notes. 5-8 marks (LAQ) = Definition, Classification, Morphology, Life cycle, Lab Diagnosis, Treatment with clear headings and diagrams.

---

MUHS 2nd MBBS - MICROBIOLOGY - PAPER 2

---

LAQ SECTION

---

Q1. 30 y/o - Muscle Twitching, Hypersalivation, Difficulty Drinking Water

---

i) Diagnosis and Etiological Agent

• Muscle twitching = neuromuscular involvement
• Hypersalivation = autonomic dysfunction + inability to swallow
• Difficulty drinking water (Hydrophobia) = pharyngeal/laryngeal spasm on seeing water - PATHOGNOMONIC of furious rabies

---

ii) Lab Diagnosis

• Ante-mortem: Saliva, CSF, serum, skin biopsy (nape of neck - hair follicles), brain biopsy
• Post-mortem: Brain tissue (hippocampus/cerebellum/brainstem = highest viral concentration)

╔═══════════════════════════════════════════════════════════════╗
║              LAB DIAGNOSIS OF RABIES                          ║
║                                                               ║
║  ANTE-MORTEM:                                                 ║
║  1. DFA (Direct Fluorescent Antibody) on skin biopsy          ║
║     - Nape of neck skin biopsy (hair follicle nerve endings)  ║
║     - Most sensitive ante-mortem test                         ║
║     - Bright apple-green fluorescence                         ║
║                                                               ║
║  2. RT-PCR (Reverse Transcriptase PCR)                        ║
║     - From saliva, CSF, skin, brain                           ║
║     - Highly sensitive, confirms genotype                     ║
║                                                               ║
║  3. Virus Isolation                                           ║
║     - Mouse inoculation / cell culture (Neuroblastoma cells)  ║
║     - From saliva, CSF                                        ║
║                                                               ║
║  4. Serology (Antibody detection)                             ║
║     - RFFIT (Rapid Fluorescent Focus Inhibition Test)         ║
║     - MNT (Mouse Neutralization Test)                         ║
║     - Useful after 7-8 days / in vaccinated individuals       ║
║     - In unvaccinated patients: antibody confirms rabies      ║
║                                                               ║
║  POST-MORTEM:                                                 ║
║  5. Negri Bodies (Seller's stain / H&E)                       ║
║     - Eosinophilic intracytoplasmic inclusion bodies          ║
║     - In Purkinje cells (cerebellum) and pyramidal cells      ║
║       of hippocampus (Ammon's horn)                           ║
║     - PATHOGNOMONIC of rabies                                 ║
║     - **Seen in the image above (dark inclusions in neurons)**║
║                                                               ║
║  6. DFA on brain tissue - GOLD STANDARD                       ║
║     - Most sensitive and specific overall test                ║
╚═══════════════════════════════════════════════════════════════╝

---

iii) DIAGRAM - Rabies Virus Structure (Easy to draw in exams)

╔═══════════════════════════════════════════════════════════════╗
║          RABIES VIRUS - BULLET SHAPE DIAGRAM                  ║
║                                                               ║
║    ╔══════════════════════════════════╗                       ║
║    ║▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓║ ← ENVELOPE             ║
║    ║ ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑  ║ ← G-PROTEIN SPIKES     ║
║    ║  ══════════════════════════     ║ ← M PROTEIN (matrix)   ║
║    ║  ●══════●══════●══════●══════   ║ ← RNP (N-protein       ║
║    ║  ●══════●══════●══════●          ║    + RNA + L/P prot)   ║
║    ║  ══════════════════════════     ║                         ║
║    ╚══════════════════════════════╝  ║                         ║
║    [FLAT END]              [ROUNDED END]                       ║
║                                                               ║
║  KEY LABELS:                                                  ║
║  • ssRNA (negative sense) → core                              ║
║  • Helical nucleocapsid (N + P + L proteins)                  ║
║  • Matrix protein (M) → inner envelope layer                  ║
║  • Glycoprotein (G) spikes → antigenicity, host attachment    ║
║  Size: 180 × 75 nm  Shape: BULLET/BACILLIFORM                 ║
╚═══════════════════════════════════════════════════════════════╝

╔══════════════════════════════════════════════╗
║        NEGRI BODY IN NEURON (DRAW THIS)      ║
║                                              ║
║   ┌──────────────────────────────────┐       ║
║   │  NEURON (hippocampal)            │       ║
║   │  Nucleus (pale) ○                │       ║
║   │                                  │       ║
║   │  ●  ← NEGRI BODY                 │       ║
║   │  (eosinophilic, cytoplasmic,     │       ║
║   │   oval/spherical inclusion)      │       ║
║   │  Contains inner granules         │       ║
║   └──────────────────────────────────┘       ║
║  Stain: Seller's stain (pink body,           ║
║         purple inner granules)               ║
╚══════════════════════════════════════════════╝

---

iv) Vaccination Scheme

1. Pre-exposure Prophylaxis (PrEP) - for high-risk people (veterinarians, lab workers, dog handlers)
2. Post-exposure Prophylaxis (PEP) - after suspected exposure

Pre-Exposure Prophylaxis (PrEP):

• HDCV (Human Diploid Cell Vaccine) OR PCECV (Purified Chick Embryo Cell Vaccine)
• Schedule: 0, 7, 28 days (3 doses IM, deltoid) → Booster every 2 years

Post-Exposure Prophylaxis (PEP) - MOST IMPORTANT:

╔══════════════════════════════════════════════════════════════╗
║            RABIES PEP SCHEDULE (ESSEN 5-DOSE)                ║
║                                                               ║
║  Day 0 → Day 3 → Day 7 → Day 14 → Day 28                    ║
║  (5 doses of cell culture vaccine - IM deltoid)              ║
║                                                               ║
║  IF Category III: Add RIG on Day 0 ONLY                      ║
║  ├── Human RIG (HRIG): 20 IU/kg (preferred)                  ║
║  └── Equine RIG (ERIG): 40 IU/kg (if HRIG unavailable)       ║
║  → Infiltrate maximum dose at wound site                      ║
║  → Remaining give IM (distant site from vaccine)             ║
║                                                               ║
║  4-DOSE schedule (Updated Essen):                            ║
║  Day 0 (2 doses - both deltoids) + Day 7 + Day 21            ║
║                                                               ║
║  WOUND MANAGEMENT (FIRST, MOST IMPORTANT):                   ║
║  • Wash with soap and water for 10-15 minutes                 ║
║  • Apply 70% alcohol/povidone-iodine                          ║
║  • Do NOT suture immediately                                  ║
╚══════════════════════════════════════════════════════════════╝

• PCECV (Rabipur/Verorab) - Intramuscular
• PVRV (Purified Vero Cell Rabies Vaccine)
• ID (Intradermal) protocol: 2-site ID schedule (0.1ml at 2 sites on day 0,3 then 1 site on day 7,28) - economical

---

---

Q2. 24 y/o male - Pain on Micturition, Pus Discharge, Contact with Sex Worker

---

i) Organism

• Family: Neisseriaceae
• Gram: Gram-negative
• Oxygen: Aerobe
• Shape: Coccus
• Fastidious: Requires enriched media

---

ii) Pathogenesis

╔══════════════════════════════════════════════════════════════════╗
║             PATHOGENESIS OF GONORRHOEA                           ║
║                                                                  ║
║  NEISSERIA GONORRHOEAE (infective dose: 100-1000 organisms)      ║
║       ↓  [Sexual contact → mucosal surface]                      ║
║  ATTACHMENT via PILI (Type IV pili = primary adhesin)            ║
║       ↓                                                          ║
║  Opa PROTEINS (outer membrane) → tight binding to               ║
║  columnar/transitional epithelium                                ║
║       ↓                                                          ║
║  PENETRATION into subepithelial tissue                           ║
║  (via endocytosis - transported across epithelial cells)         ║
║       ↓                                                          ║
║  INFLAMMATORY RESPONSE:                                          ║
║  PMN influx → intense neutrophilic reaction                      ║
║  Gonococcal LOS (lipooligosaccharide) → TNF release → damage     ║
║       ↓                                                          ║
║  PUS FORMATION (urethral discharge)                              ║
║       ↓                                                          ║
║  Local spread → ascending infection:                             ║
║  Male: Epididymitis, Prostatitis, Urethral stricture             ║
║  Female: PID, Salpingitis, Bartholin's gland abscess             ║
║  Systemic: DGI (Disseminated Gonococcal Infection)               ║
║            → Septic arthritis, Skin lesions, Endocarditis        ║
╚══════════════════════════════════════════════════════════════════╝

---

iii) Lab Diagnosis

╔══════════════════════════════════════════════════════════════╗
║           LAB DIAGNOSIS OF GONORRHOEA                        ║
║                                                              ║
║  1. GRAM STAIN (MOST IMPORTANT - quick diagnosis)            ║
║     - Urethral pus smear                                     ║
║     - Gram-negative diplococci WITHIN PMNs                   ║
║     - Sensitivity: 90-95% in symptomatic males               ║
║     - Less sensitive in females (50-70%)                     ║
║                                                              ║
║  2. CULTURE (GOLD STANDARD):                                 ║
║     Media: Modified Thayer-Martin (MTM) medium               ║
║     = Chocolate agar + VCN inhibitors:                       ║
║       Vancomycin (gram +ve), Colistin (gram -ve),            ║
║       Nystatin (fungi) + Trimethoprim                        ║
║     Transport: Stuart's transport medium (if delay)          ║
║     Incubate: 35-37°C, 5-10% CO2 atmosphere (candle jar)    ║
║     Colonies: Small, grey, translucent, oxidase +ve          ║
║                                                              ║
║  3. BIOCHEMICAL:                                             ║
║     - Oxidase POSITIVE (key test)                            ║
║     - Ferments GLUCOSE only (not maltose/lactose)            ║
║       (N. meningitidis ferments glucose AND maltose)         ║
║     - Catalase positive                                      ║
║                                                              ║
║  4. NUCLEIC ACID AMPLIFICATION TEST (NAAT) - BEST OVERALL:  ║
║     - PCR/SDA/TMA on urine or swab                           ║
║     - Highest sensitivity and specificity                    ║
║     - Can detect both N. gonorrhoeae AND C. trachomatis       ║
║       simultaneously (co-infection common)                   ║
║     - Does NOT require viable organisms                      ║
║                                                              ║
║  5. OXIDASE TEST:                                            ║
║     - Tetramethyl-p-phenylenediamine (reagent)               ║
║     - Colonies turn PURPLE = oxidase positive                ║
╚══════════════════════════════════════════════════════════════╝

• Ceftriaxone 500mg IM single dose (DOC - due to QRNG - quinolone-resistant N. gonorrhoeae)
• + Azithromycin 1g oral (for co-infection with Chlamydia)
• Neonatal ophthalmia: 1% Silver nitrate drops / Erythromycin eye ointment

---

iv) DIAGRAM - Gram Stain of Gonorrhoea (Draw in exam)

╔══════════════════════════════════════════════════════════════╗
║    GRAM STAIN DIAGRAM - N. GONORRHOEAE IN PUS                ║
║                                                              ║
║  PINK background (gram-negative)                             ║
║                                                              ║
║  ┌─────────────────────┐                                     ║
║  │      PMN (pink)     │                                     ║
║  │  Nucleus - lobed    │                                     ║
║  │     @  @  @         │                                     ║
║  │  ← coffee bean      │                                     ║
║  │     diplococci      │                                     ║
║  │  (INTRACELLULAR)    │                                     ║
║  └─────────────────────┘                                     ║
║                                                              ║
║  ALSO extracellular diplococci seen                          ║
║                                                              ║
║  KEY:                                                        ║
║  @@ = gram-negative diplococcus (coffee bean shape)          ║
║  Flat adjacent sides facing each other                       ║
║  PINK = gram-negative (safranin)                             ║
║  Diplococci found WITHIN the cytoplasm of PMNs               ║
╚══════════════════════════════════════════════════════════════╝

---

---

Q3. 12 days ago - Contact with Sex Worker - Indurated Painless Ulcer

---

i) Diagnosis

---

ii) Clinical Features in Different Stages

╔══════════════════════════════════════════════════════════════════╗
║           STAGES OF SYPHILIS - CLINICAL FEATURES                 ║
║                                                                  ║
║  ┌─────────────────────────────────────────────────────────┐     ║
║  │ PRIMARY SYPHILIS (Week 1-12 after infection):           │     ║
║  │ • Single PAINLESS, INDURATED (hard) ulcer = CHANCRE     │     ║
║  │ • Site: Glans penis, vulva, vagina, cervix, anus         │     ║
║  │ • Non-tender, clean base, raised edges                   │     ║
║  │ • Regional LYMPHADENOPATHY (painless, firm)             │     ║
║  │ • Heals spontaneously in 3-6 weeks                       │     ║
║  └─────────────────────────────────────────────────────────┘     ║
║           ↓ (if untreated, 4-8 weeks later)                      ║
║  ┌─────────────────────────────────────────────────────────┐     ║
║  │ SECONDARY SYPHILIS (Weeks 6-8 after chancre heals):     │     ║
║  │ • SKIN RASH: maculopapular, INVOLVES PALMS AND SOLES    │     ║
║  │   (pathognomonic finding)                               │     ║
║  │ • Condylomata lata (moist, warty plaques in perineum)   │     ║
║  │ • Mucous patches in mouth (HIGHLY INFECTIOUS)           │     ║
║  │ • Generalized lymphadenopathy                           │     ║
║  │ • Alopecia (moth-eaten)                                  │     ║
║  │ • Flu-like symptoms: fever, malaise, headache           │     ║
║  │ • Hepatitis, meningitis, uveitis (rare)                  │     ║
║  └─────────────────────────────────────────────────────────┘     ║
║           ↓ (latent period: 2 years early, >2 years late)        ║
║  ┌─────────────────────────────────────────────────────────┐     ║
║  │ LATENT SYPHILIS:                                        │     ║
║  │ • Early latent (<2 years): Asymptomatic, can relapse    │     ║
║  │ • Late latent (>2 years): No symptoms, low infectivity  │     ║
║  └─────────────────────────────────────────────────────────┘     ║
║           ↓ (years later)                                        ║
║  ┌─────────────────────────────────────────────────────────┐     ║
║  │ TERTIARY/LATE SYPHILIS:                                  │     ║
║  │ • GUMMA (granulomatous lesions): skin, bone, liver      │     ║
║  │ • Cardiovascular syphilis:                              │     ║
║  │   - Aortic aneurysm (ascending aorta)                   │     ║
║  │   - Aortic regurgitation                                │     ║
║  │   - Coronary ostial stenosis                            │     ║
║  │ • Neurosyphilis:                                        │     ║
║  │   - Meningovascular syphilis                            │     ║
║  │   - General paresis of the insane (GPI)                 │     ║
║  │   - Tabes dorsalis (posterior column degeneration)      │     ║
║  │   - Argyll Robertson pupil (accommodates but doesn't    │     ║
║  │     react to light)                                     │     ║
║  └─────────────────────────────────────────────────────────┘     ║
║                                                                  ║
║  CONGENITAL SYPHILIS (Transplacental):                           ║
║  EARLY (<2 years): Snuffles, condylomata, rash, hepato-          ║
║         splenomegaly, osteochondritis, pseudoparalysis           ║
║  LATE (>2 years): Hutchinson's triad:                            ║
║   1. Interstitial keratitis                                      ║
║   2. 8th nerve deafness                                          ║
║   3. Hutchinson's teeth (peg-shaped notched incisors)           ║
╚══════════════════════════════════════════════════════════════════╝

---

iii) Lab Diagnosis

╔══════════════════════════════════════════════════════════════════╗
║           LAB DIAGNOSIS OF SYPHILIS                              ║
║                                                                  ║
║  A. DIRECT DETECTION (Primary/Secondary - infectious stages):    ║
║                                                                  ║
║  1. DARK-FIELD MICROSCOPY (MOST IMPORTANT for primary)           ║
║     - Exudate from chancre/condylomata                           ║
║     - Spirochetes seen as white, corkscrew, rotatory organisms   ║
║     - IMMEDIATE examination required                             ║
║     - Cannot use on oral lesions (commensal treponemes           ║
║       may give false positive)                                   ║
║                                                                  ║
║  2. DFA-TP (Direct Fluorescent Antibody for T. pallidum)         ║
║     - Fixed smear + fluorescent anti-Tp antibody                 ║
║     - Can use on oral lesions (species-specific)                 ║
║                                                                  ║
║  3. PCR - Highly sensitive, from ulcer exudate                   ║
║                                                                  ║
║  B. SEROLOGICAL TESTS:                                           ║
║                                                                  ║
║  NON-TREPONEMAL (REAGINIC) TESTS - SCREENING:                    ║
║  ├── VDRL (Venereal Disease Research Laboratory)                 ║
║  │   - Cardiolipin-lecithin-cholesterol antigen                  ║
║  │   - Flocculation test (tubes/slides)                          ║
║  │   - POSITIVE: clumping = reactive                             ║
║  │   - Used for: SCREENING + CSF (neurosyphilis)                 ║
║  └── RPR (Rapid Plasma Reagin)                                   ║
║      - Carbon particles + cardiolipin antigen                    ║
║      - Can be done on unheated serum (rapid)                     ║
║      - Preferred for field screening                             ║
║                                                                  ║
║  TREPONEMAL (SPECIFIC) TESTS - CONFIRMATORY:                     ║
║  ├── TPHA/TPPA (T. pallidum Hemagglutination/Particle           ║
║  │   Passive Agglutination) - simple, widely used               ║
║  ├── FTA-ABS (Fluorescent Treponemal Antibody-Absorbed)          ║
║  │   - GOLD STANDARD, first to become positive,                  ║
║  │     remains positive lifelong                                 ║
║  ├── ELISA (anti-Tp antibody)                                    ║
║  └── Western Blot (most specific)                                ║
╚══════════════════════════════════════════════════════════════════╝

• SLE, malaria, leprosy, pregnancy, viral infections (EBV, hepatitis), old age

• VDRL on CSF = GOLD STANDARD for neurosyphilis
• Lymphocytic pleocytosis, elevated protein

• Primary/Secondary/Early latent: Benzathine Penicillin G 2.4 MU IM single dose
• Late latent/Tertiary: Benzathine Penicillin G 2.4 MU IM weekly x 3 doses
• Neurosyphilis: Aqueous Penicillin G 18-24 MU/day IV x 10-14 days
• Penicillin allergy: Doxycycline 100mg BD x 14-28 days

---

iv) Mode of Transmission (MOT)

• Toilet seats, swimming pools, sharing utensils (organism dies rapidly on drying)

---

---

SAQ SECTION

---

SAQ 1: Short Note on TUBERCULIN TEST (Mantoux Test)

Principle:

• Type IV hypersensitivity (Delayed Type Hypersensitivity - DTH)
• Mediated by sensitized T lymphocytes (CD4+ Th1 cells)
• Previous exposure to TB antigens → memory T cells formed
• Re-injection of tuberculin antigen → memory T cells recruited → cytokines released → induration (hard swelling) at injection site
• Induration (not erythema) = measure of positivity

Procedure:

╔══════════════════════════════════════════════════════════════╗
║              MANTOUX TEST PROCEDURE                          ║
║                                                              ║
║  MATERIAL: 0.1 mL of PPD (Purified Protein Derivative)       ║
║             = 5 TU (Tuberculin Units) in India               ║
║                                                              ║
║  SITE: Volar surface of left forearm                         ║
║                                                              ║
║  TECHNIQUE: INTRADERMAL (NOT subcutaneous)                   ║
║  → Inject using 26-gauge needle                              ║
║  → Wheal 6-10 mm should appear                               ║
║                                                              ║
║  READ at: 48-72 hours                                        ║
║                                                              ║
║  MEASURE: Only INDURATION (hard area) with ruler              ║
║           NOT redness/erythema                               ║
╚══════════════════════════════════════════════════════════════╝

Interpretation (Indian guidelines / WHO):

False POSITIVE causes:

• BCG vaccination
• NTM (Non-tuberculous mycobacteria) infection
• Cross-reaction with other Mycobacteria

False NEGATIVE causes (Anergy):

Mnemonic: LIMED-V
L - Lymphoma / leukemia
I - Immunosuppression (HIV, steroids, chemotherapy)
M - Malnutrition
E - Early TB (< 6 weeks)
D - Disseminated TB (miliary - energy state)
V - Viral infections (measles, mumps)

Applications:

1. Screening for latent TB infection (LTBI)
2. Contact tracing (index case contacts)
3. Diagnosis in children (< 5 years, no BCG = strong indicator)
4. Epidemiological surveys (prevalence of TB infection)
5. Pre-BCG testing in older children (>5 years)
6. Evidence of CMI in TB research/teaching
7. NOT useful to diagnose active TB (positive only means past exposure)

---

SAQ 2: Diphtheria Prophylaxis - Rationale and Types

• Disease is caused by exotoxin (not organism itself)
• Antitoxin neutralizes circulating toxin
• Vaccine induces antitoxin antibodies → prevents disease
• Herd immunity needed (>85% coverage eliminates circulation)
• Immunisation with toxoid (formalin-inactivated toxin) is mainstay

Types of Prophylaxis:

╔══════════════════════════════════════════════════════════════════╗
║           DIPHTHERIA PROPHYLAXIS                                  ║
║                                                                   ║
║  A. ACTIVE IMMUNIZATION (Long-term, preferred):                   ║
║  ├── Diphtheria Toxoid (DT/dT component)                         ║
║  │   - Toxin treated with formalin → TOXOID                      ║
║  │   - Non-toxic but immunogenic                                  ║
║  │   - Induces antitoxin (IgG) antibodies                        ║
║  │   - Combined vaccines used:                                    ║
║  │     • DPT (Diphtheria + Pertussis + Tetanus) - children       ║
║  │     • Tdap - adolescents/adults (lower dose dT)               ║
║  │                                                               ║
║  NATIONAL IMMUNIZATION SCHEDULE (India):                         ║
║  DPT:  6 weeks, 10 weeks, 14 weeks (primary series)              ║
║        18 months (1st booster)                                   ║
║        5 years (2nd booster - DT/DPT)                            ║
║        10 years + 16 years (dT booster)                          ║
║                                                                   ║
║  B. PASSIVE IMMUNIZATION (Short-term, immediate):                 ║
║  ├── DAT (Diphtheria Antitoxin) = Antidiphtheritic serum (ADS)   ║
║  │   - Equine (horse) antiserum containing anti-diphtheria IgG   ║
║  │   - Used for: TREATMENT of clinical diphtheria                ║
║  │   - MUST test for horse serum allergy first (ID test)         ║
║  │   - Dose: 20,000-1,00,000 units depending on severity         ║
║  │   - Given IM or IV                                            ║
║  │   - Neutralizes FREE toxin (not toxin already bound to cells) ║
║  │                                                               ║
║  C. CHEMOPROPHYLAXIS (for close contacts):                        ║
║  └── Erythromycin 500mg QID x 7 days OR                          ║
║      Benzathine Penicillin G 1.2 MU IM single dose               ║
║      (eradicates carriage)                                        ║
╚══════════════════════════════════════════════════════════════════╝

• Inject 1/50 MLD of diphtheria toxin intradermally
• Positive (susceptible) = red inflamed area at 24-48h (no antitoxin = no protection)
• Negative (immune) = no reaction (antitoxin present)
• Rarely used today (replaced by serology)

---

SAQ 3: Methods of MRSA Detection and Prevention of Spread

Types:

• HA-MRSA (Hospital-Acquired): Affects hospitalized patients, immunocompromised
• CA-MRSA (Community-Acquired): Affects healthy individuals; Panton-Valentine Leukocidin (PVL) toxin positive

Methods of MRSA Detection:

╔═══════════════════════════════════════════════════════════════╗
║             METHODS OF MRSA DETECTION                         ║
║                                                               ║
║  1. CONVENTIONAL CULTURE + SUSCEPTIBILITY:                    ║
║     a. Culture on ChromoAgar MRSA (chromogenic):              ║
║        - MRSA colonies → MAUVE/PINK color                     ║
║        - Sensitivity ~75-90%, specific                        ║
║     b. Blood agar → identify S. aureus                        ║
║        → Disk Diffusion: Oxacillin/Cefoxitin disk (30μg)      ║
║        - Zone <22mm (Cefoxitin) = MRSA                        ║
║        - Cefoxitin is best predictor of mecA gene             ║
║     c. MIC (Minimum Inhibitory Concentration):                ║
║        - Oxacillin MIC ≥4 μg/mL = MRSA                       ║
║                                                               ║
║  2. MOLECULAR METHODS (GOLD STANDARD):                        ║
║     a. PCR for mecA gene (most definitive)                    ║
║     b. Real-time PCR (BD GeneOhm, Xpert MRSA) - rapid        ║
║        (2-5 hours) from nasal swabs                           ║
║     c. Results in 2-3 hours - used for active surveillance    ║
║                                                               ║
║  3. LATEX AGGLUTINATION:                                      ║
║     - Detects PBP2a (mecA gene product)                       ║
║     - e.g. MRSA Screen test (Denka Seiken)                    ║
║     - Quick, cheap, easy to perform                           ║
║                                                               ║
║  4. ANTI-PBP2a IMMUNOASSAY:                                   ║
║     - Lateral flow assay or ELISA for PBP2a protein          ║
║     - From colonies after 6-hour enrichment                   ║
╚═══════════════════════════════════════════════════════════════╝

Recommendations to Prevent MRSA Spread (Infection Control):

PREVENTION STRATEGIES:

STANDARD PRECAUTIONS (ALL patients):
• Hand hygiene (WHO 6 steps) - MOST IMPORTANT
• PPE (gloves, gown) when handling body fluids
• Safe sharps disposal

CONTACT PRECAUTIONS (MRSA patients):
• ISOLATE patient in single room (or cohort MRSA patients)
• Gloves + gown for ALL contact
• Dedicated equipment (stethoscope, BP cuff)
• Decolonization:
  - Mupirocin 2% nasal ointment BD x 5 days
  - Chlorhexidine 2-4% whole body wash x 5 days
  - Screen household contacts

ACTIVE SURVEILLANCE CULTURES (ASC):
• Screen all ICU admissions (nasal + rectal swab)
• Identify MRSA carriers → isolate/decolonize

ANTIMICROBIAL STEWARDSHIP:
• Restrict broad-spectrum antibiotics
• Rotate antibiotics in ICU
• Remove unnecessary catheters/lines

TREATMENT of MRSA infections:
• Vancomycin IV (DOC for serious HA-MRSA)
• Linezolid (oral/IV; skin and soft tissue)
• Daptomycin (bacteremia, endocarditis)
• Trimethoprim-Sulfa (CA-MRSA skin infections)

---

SAQ 4: Serological Markers in Hepatitis B Infection

• DNA virus, Hepadnaviridae family
• Antigens: HBsAg, HBcAg, HBeAg (important serological markers)

DIAGRAM - HBV Structure:

╔═══════════════════════════════════════════════════════╗
║         HBV PARTICLE (DANE PARTICLE) DIAGRAM          ║
║                                                       ║
║   OUTER ENVELOPE:  ●●●●●●●●●  ← HBsAg                ║
║   INNER CORE:      ████████   ← HBcAg (internal)     ║
║   Within core:     ════════   ← HBeAg (soluble)      ║
║                     |   |                            ║
║                    dsDNA + DNA polymerase             ║
╚═══════════════════════════════════════════════════════╝

Serological Markers Table (MOST IMPORTANT - must memorise):

╔══════════════════════════════════════════════════════════════════════════╗
║               HBV SEROLOGICAL MARKERS - INTERPRETATION                   ║
╠═══════════════╦═══════╦═══════╦═══════╦════════╦════════╦═══════════════╣
║ STATUS        ║HBsAg  ║Anti-  ║HBeAg  ║Anti-   ║Anti-   ║ HBV DNA       ║
║               ║       ║HBs    ║       ║HBe     ║HBc     ║               ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Susceptible   ║  -    ║  -    ║  -    ║   -    ║  -     ║   -           ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Acute HBV     ║  +    ║  -    ║  +    ║   -    ║IgM+ve  ║ High          ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Chronic HBV   ║  +    ║  -    ║  +/-  ║   +/-  ║IgG+ve  ║ +/-           ║
║ (High replic) ║  +    ║  -    ║  +    ║   -    ║IgG+ve  ║ High          ║
║ (Low replic)  ║  +    ║  -    ║  -    ║   +    ║IgG+ve  ║ Low/undetect  ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Window period ║  -    ║  -    ║  -    ║   -    ║IgM+ve  ║ +             ║
║ (acute phase) ║       ║       ║       ║        ║(ONLY+) ║               ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Past infection║  -    ║  +    ║  -    ║   +/-  ║IgG+ve  ║   -           ║
║ (resolved)    ║       ║       ║       ║        ║        ║               ║
╠═══════════════╬═══════╬═══════╬═══════╬════════╬════════╬═══════════════╣
║ Vaccinated    ║  -    ║  +    ║  -    ║   -    ║  -     ║   -           ║
║ (only anti-HBs positive; no anti-HBc = NOT naturally infected)           ║
╚══════════════════════════════════════════════════════════════════════════╝

Individual Marker Significance:

• HBsAg disappears, Anti-HBs not yet formed
• Anti-HBc IgM is the ONLY positive marker - sole evidence of infection
• Important in blood bank screening (NAT used to cover window period)

• Anti-HBs titre >10 IU/mL = seroprotected/immune

---

SAQ 5: 4 Viruses Responsible for Carcinoma + HSV-2

Oncogenic Viruses (Tumour Viruses):

╔══════════════════════════════════════════════════════════════════╗
║           4 VIRUSES RESPONSIBLE FOR CARCINOMA                    ║
║                                                                  ║
║  1. HPV (Human Papillomavirus)                                   ║
║     Type: DNA virus; double-stranded                             ║
║     Family: Papillomaviridae                                     ║
║     Tumours:                                                     ║
║     • Cervical carcinoma (HPV 16, 18 = 70% of cases)            ║
║     • Anal, vulvar, vaginal, penile carcinoma                    ║
║     • Oropharyngeal cancer (HPV 16)                              ║
║     Mechanism: E6 protein → degrades p53 (tumour suppressor)    ║
║                E7 protein → binds Rb protein → uncontrolled     ║
║                cell cycle                                        ║
║                                                                  ║
║  2. EBV (Epstein-Barr Virus)                                     ║
║     Type: DNA virus (Herpesvirus)                                ║
║     Tumours:                                                     ║
║     • Burkitt's lymphoma (African jaw tumour - EBV + malaria)    ║
║     • Nasopharyngeal carcinoma                                   ║
║     • Hodgkin's lymphoma                                         ║
║     • Post-transplant lymphoma                                   ║
║     Mechanism: Immortalizes B cells; expresses LMP-1 (NF-kB     ║
║                activation); EBNA (nuclear antigen)               ║
║                                                                  ║
║  3. HBV (Hepatitis B Virus)                                      ║
║     Type: DNA virus (Hepadnaviridae)                             ║
║     Tumour: Hepatocellular carcinoma (HCC)                       ║
║     Risk: Chronic HBV → cirrhosis → HCC                         ║
║     Also: HCV → HCC                                              ║
║     Mechanism: HBx protein → p53 inactivation; insertional      ║
║                mutagenesis; chronic inflammation                 ║
║                                                                  ║
║  4. HTLV-1 (Human T-cell Lymphotropic Virus Type 1)              ║
║     Type: RNA virus (Retrovirus)                                  ║
║     Tumour: Adult T-cell Leukemia/Lymphoma (ATL)                 ║
║     Endemic: Japan, Caribbean, Africa                            ║
║     Also: HTLV-1 Associated Myelopathy (HAM/TSP)                ║
║     Mechanism: Tax protein → activates NF-kB; IL-2 receptor;    ║
║                polyclonal T-cell expansion → clonal malignancy   ║
╚══════════════════════════════════════════════════════════════════╝

Additional oncogenic viruses (if asked in exam):

• KSHV/HHV-8 → Kaposi's sarcoma (common in AIDS)
• MCPyV (Merkel Cell Polyomavirus) → Merkel cell carcinoma
• HCV → Hepatocellular carcinoma

HSV-2 and Carcinoma:

• Primary: Painful vesicles/ulcers on genitalia, fever, inguinal lymphadenopathy
• Recurrent: Milder, prodrome of tingling/burning
• Neonatal: Via infected birth canal → severe disseminated/CNS disease

• Cervical carcinoma: HSV-2 was formerly considered causative; currently thought to act as a co-factor alongside HPV (promotes HPV oncogenesis)
• HSV-2 seropositivity is associated with increased cervical cancer risk
• Not directly oncogenic like HPV but enhances malignant transformation

• Tzanck smear: Multinucleated giant cells with intranuclear inclusions (Cowdry type A)
• PCR from vesicle fluid (most sensitive)
• Viral culture (gold standard)
• Serology (IgM/IgG ELISA - type specific)

---

SAQ 6: Short Note on Zoonotic Diseases

╔══════════════════════════════════════════════════════════════════╗
║                CLASSIFICATION OF ZOONOSES                        ║
║                                                                  ║
║  1. DIRECT ZOONOSES (Simple host cycle):                         ║
║     One vertebrate + man                                         ║
║     Ex: Rabies (dog→man), Brucellosis, Leptospirosis             ║
║                                                                  ║
║  2. CYCLOZOONOSES (Multiple vertebrate hosts):                   ║
║     Require >1 vertebrate host                                   ║
║     Ex: Taenia solium (pig→man), Echinococcosis (sheep→man)      ║
║                                                                  ║
║  3. METAZOONOSES (Arthropod vector required):                    ║
║     Vertebrate → Arthropod vector → Man                          ║
║     Ex: Malaria, Dengue, Plague, Rickettsial diseases            ║
║         Yellow fever, Japanese encephalitis, Scrub typhus        ║
║                                                                  ║
║  4. SAPROZOONOSES (Abiotic reservoir):                           ║
║     Soil/plant + vertebrate + man                                ║
║     Ex: Histoplasmosis (soil/bird droppings), Aspergillosis      ║
╚══════════════════════════════════════════════════════════════════╝

Important Zoonoses (MUHS High Yield Table):

Examples of Emerging Zoonoses (Important for exams):

• SARS-CoV-2: Bats (origin), zoonotic spillover
• Nipah: Bats → Pigs → Humans
• MERS-CoV: Camels → Humans
• Ebola: Bats/fruit bats → Primates → Humans
• Monkeypox: Rodents, non-human primates

Public Health Significance:

• Zoonoses account for ~60% of all emerging infectious diseases
• Control requires One Health approach (human + animal + environment health integrated)
• Surveillance of animal populations, vector control, vaccination (rabies), food safety

---

References: Apurba Shastri's Textbook of Microbiology; Jawetz Melnick & Adelberg's Medical Microbiology 28th Ed; Murray Medical Microbiology 9e; Bradley & Daroff's Neurology; WHO Rabies Post-Exposure Prophylaxis Guidelines.

MUHS Exam Tip: For STI questions (Gonorrhoea/Syphilis) - always begin with morphology, then pathogenesis, then lab diagnosis with table. For Rabies - always include Negri bodies and PEP schedule. For Hepatitis B - the serological markers table is the highest-yield single topic in virology - memorise it completely.

---

MUHS 2nd MBBS - MICROBIOLOGY - EXTENDED QUESTION BANK

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Q7. SHORT NOTE ON ZOONOTIC DISEASES

• Definition: Infections naturally transmissible from vertebrate animals to humans
• Types: Direct, Cyclo-, Meta-, Saprozoonoses
• Key examples: Rabies (dog), Leptospirosis (rat), Plague (rat→flea→man), Brucellosis (cattle), Toxoplasmosis (cat), Scrub typhus (rodents→chigger)
• One Health concept - integrated human-animal-environment health approach

---

Q8. CLASSIFY ENTEROVIRUS; DETAIL ABOUT POLIO VACCINES

Classification of Enteroviruses:

╔══════════════════════════════════════════════════════════════════╗
║              CLASSIFICATION OF ENTEROVIRUS                       ║
║  Family: Picornaviridae (Pico = small; RNA = RNA genome)         ║
║  Genus: Enterovirus                                              ║
║                                                                  ║
║  SUBGROUPS:                                                      ║
║  ┌──────────────────────────────────────────────────────┐        ║
║  │ 1. POLIOVIRUS (Types 1, 2, 3)                        │        ║
║  │    Type 1 = Brunhilde = most epidemic                │        ║
║  │    Type 2 = Lansing = eradicated 2015                │        ║
║  │    Type 3 = Leon                                     │        ║
║  │                                                      │        ║
║  │ 2. COXSACKIEVIRUS                                    │        ║
║  │    Group A (23 serotypes): Hand, Foot & Mouth (A16)  │        ║
║  │    Herpangina, Aseptic meningitis                    │        ║
║  │    Group B (6 serotypes): Myocarditis, Pleurodynia,  │        ║
║  │    Bornholm disease, Meningoencephalitis             │        ║
║  │                                                      │        ║
║  │ 3. ECHOVIRUS (31 serotypes)                          │        ║
║  │    Aseptic meningitis, respiratory infections,       │        ║
║  │    diarrhea in infants                               │        ║
║  │                                                      │        ║
║  │ 4. ENTEROVIRUS (numbered serotypes)                  │        ║
║  │    EV-70: Acute hemorrhagic conjunctivitis           │        ║
║  │    EV-71: Hand-foot-mouth disease (severe CNS form)  │        ║
║  │    EV-68: Acute flaccid myelitis (AFP)               │        ║
║  └──────────────────────────────────────────────────────┘        ║
║                                                                  ║
║  PROPERTIES (common to all):                                     ║
║  • Single-stranded, positive-sense RNA                           ║
║  • Non-enveloped, icosahedral capsid                             ║
║  • Small (25-30 nm)                                              ║
║  • Resistant to ether, acid, detergents                          ║
║  • Habitat: Intestinal tract → name "Entero"virus                ║
╚══════════════════════════════════════════════════════════════════╝

---

POLIOVIRUS - DETAIL:

╔══════════════════════════════════════════════════════════════╗
║         PATHOGENESIS OF POLIOMYELITIS                        ║
║                                                              ║
║  INGESTION of virus (feco-oral route)                        ║
║       ↓                                                      ║
║  Oropharynx → tonsils + Peyer's patches (M cells)           ║
║       ↓ Primary viremia                                      ║
║  Blood (minor viremia) → Reticuloendothelial system          ║
║       ↓ (in ~1% cases)                                       ║
║  MAJOR VIREMIA → CNS invasion                                ║
║       ↓ via blood-brain barrier                              ║
║  MOTOR NEURONS (anterior horn cells) of spinal cord          ║
║       ↓ viral replication → cell death                       ║
║  FLACCID PARALYSIS (Lower Motor Neuron type)                 ║
║                                                              ║
║  Outcomes (infection pyramid):                               ║
║  • 90-95%: Subclinical (no symptoms)                         ║
║  • 4-8%: Abortive polio (minor illness - fever, malaise)     ║
║  • 1-2%: Non-paralytic (aseptic meningitis)                  ║
║  • 0.1-1%: Paralytic polio (flaccid paralysis)               ║
╚══════════════════════════════════════════════════════════════╝

---

POLIO VACCINES (HIGH YIELD COMPARISON):

╔══════════════════════════════════════════════════════════════════════╗
║         OPV vs IPV - COMPARISON TABLE                                ║
╠═════════════════════════╦═════════════════╦════════════════════════╣
║ Feature                 ║ OPV (Sabin)      ║ IPV (Salk)             ║
╠═════════════════════════╬═════════════════╬════════════════════════╣
║ Type                    ║ Live attenuated  ║ Killed/inactivated      ║
║ Route                   ║ Oral (drops)     ║ Intramuscular injection ║
║ Dose                    ║ 2 drops          ║ 0.5 ml IM               ║
║ Immunity                ║ Humoral + mucosal║ Humoral only            ║
║                         ║ (IgA in gut)     ║ (no mucosal IgA)        ║
║ Herd immunity           ║ EXCELLENT        ║ Poor                    ║
║                         ║ (virus shed in  ║                         ║
║                         ║ stool → spreads) ║                         ║
║ VAPP risk               ║ YES (1:750,000)   ║ NO (killed virus)       ║
║ cVDPV risk              ║ YES              ║ NO                      ║
║ Cold chain              ║ Strict (-20°C)   ║ Less strict (+4°C)      ║
║ Cost                    ║ Cheap            ║ Expensive               ║
║ WHO preference          ║ Eradication prog ║ High-income countries   ║
╚═════════════════════════╩═════════════════╩════════════════════════╝

• tOPV (trivalent): Types 1+2+3 - used till 2016
• bOPV (bivalent): Types 1+3 - currently used (type 2 eradicated in 2015)
• mOPV (monovalent): Single type - outbreak response

• Risk: 1 per 2.4 million doses
• Usually type 3 OPV strain reverts to neurovirulence
• Higher risk in: first dose recipients, immunocompromised

India's Polio Immunization Schedule:

NATIONAL IMMUNIZATION PROGRAMME (India):
At Birth: OPV (birth dose)
6 weeks: IPV 1 + OPV 1 (fractional IPV 0.1ml ID)
10 weeks: OPV 2
14 weeks: IPV 2 + OPV 3 (fIPV 0.1ml ID)
Pulse Polio: Annual January/February NIDs (National Immunization Days)

• fIPV (fractional dose intradermally 0.1ml) added to reduce cost
• Provides systemic immunity without mucosal immunity

• India: Polio-free since January 2011 (last case Jan 2011, certified 2014)
• Global: Types 2 and 3 wild poliovirus eradicated; Type 1 persists in Pakistan/Afghanistan

---

Q9. NOTE ON OCULAR FUNGAL INFECTION

Classification by site:

╔══════════════════════════════════════════════════════════════════╗
║           OCULAR FUNGAL INFECTIONS                               ║
║                                                                  ║
║  A. FUNGAL KERATITIS (Mycotic keratitis):                        ║
║     MOST COMMON ocular fungal infection                          ║
║     Organisms:                                                   ║
║     ├── FILAMENTOUS fungi (tropical regions, India):             ║
║     │   • Fusarium solani (most common worldwide)                ║
║     │   • Aspergillus fumigatus                                  ║
║     │   • Curvularia, Alternaria (dematiaceous)                  ║
║     └── YEAST (temperate, immunocompromised):                    ║
║         • Candida albicans                                       ║
║                                                                  ║
║  B. ENDOPHTHALMITIS:                                             ║
║     Candida (most common - via blood, IV drug users)             ║
║     Aspergillus (trauma/surgery)                                 ║
║                                                                  ║
║  C. ORBITAL CELLULITIS / RHINOCEREBRAL:                          ║
║     Mucor/Rhizopus (Mucormycosis) - diabetics, ketoacidosis      ║
║                                                                  ║
║  D. CONJUNCTIVITIS: Candida, Aspergillus (rare)                  ║
╚══════════════════════════════════════════════════════════════════╝

Risk Factors:

• Corneal trauma (vegetative matter - thorn, leaf - Fusarium)
• Contact lens wear
• Previous corneal surgery
• Topical steroid use
• Immunocompromise (Candida, Aspergillus)
• Diabetes (Mucormycosis)

Clinical Features of Fungal Keratitis:

• Corneal ulcer with feathery/satellite lesions (filamentous)
• Dry, raised, grey-white infiltrate
• Hypopyon (pus in anterior chamber)
• Slow progression (unlike bacterial keratitis)
• Poor response to antibacterial therapy

Lab Diagnosis:

SPECIMEN: Corneal scraping (from base and edges of ulcer)
           by slit-lamp under sterile conditions

1. DIRECT MICROSCOPY:
   ├── KOH mount (10-20%): Branching hyphae or yeast cells
   ├── Gram stain: Gram +ve fungal elements
   ├── Giemsa stain: Good for Candida
   ├── Calcoflour white (fluorescent): Most sensitive
   └── H&E on biopsy specimen

2. CULTURE:
   ├── SDA (Sabouraud's Dextrose Agar) at 25°C and 37°C
   ├── BHI agar
   ├── Report: Colony morphology, colour, rate of growth
   └── LPCB (Lactophenol Cotton Blue) for microscopic ID

3. CONFOCAL MICROSCOPY (in vivo):
   - Non-invasive; detects hyphae in living cornea
   - Increasingly used in India

4. PCR: From corneal scraping - highly specific

• Natamycin 5% eye drops (DOC for filamentous fungi - Fusarium, Aspergillus)
• Voriconazole (topical/systemic) - broad spectrum
• Fluconazole (Candida keratitis)
• Amphotericin B (severe/Candida)
• Mucormycosis: Urgent surgical debridement + Liposomal Amphotericin B IV

---

Q10. DEFINE AND CLASSIFY HOSPITAL-ACQUIRED INFECTION (HAI); DESCRIBE ONE IN DETAIL

Definition:

Classification:

╔══════════════════════════════════════════════════════════════════╗
║            CLASSIFICATION OF NOSOCOMIAL INFECTIONS               ║
║                                                                  ║
║  BY SITE:                                                        ║
║  1. CAUTI - Catheter-Associated Urinary Tract Infection (31%)    ║
║  2. SSI - Surgical Site Infection (20%)                          ║
║  3. VAP - Ventilator-Associated Pneumonia (15%)                  ║
║  4. CLABSI - Central Line-Associated Bloodstream Infection (14%) ║
║  5. C. difficile Infection (CDI) (8%)                            ║
║                                                                  ║
║  BY SOURCE:                                                      ║
║  • Endogenous: Patient's own flora (most common)                 ║
║  • Exogenous: Environment, staff, equipment                      ║
║                                                                  ║
║  BY ORGANISMS (ESKAPE pathogens):                                ║
║  E - Enterococcus faecium (VRE)                                  ║
║  S - Staphylococcus aureus (MRSA)                                ║
║  K - Klebsiella pneumoniae (ESBL, carbapenem-resistant)          ║
║  A - Acinetobacter baumannii (MDR)                               ║
║  P - Pseudomonas aeruginosa (MDR)                                ║
║  E - Enterobacter species                                        ║
╚══════════════════════════════════════════════════════════════════╝

---

CAUTI - Catheter-Associated UTI (IN DETAIL):

• Most common HAI worldwide (31% of all HAIs)
• Risk: 3-7% per catheter-day
• Accounts for 80% of hospital-acquired UTIs

╔════════════════════════════════════════════════════════╗
║         CAUTI PATHOGENESIS                             ║
║                                                        ║
║  EXTRALUMINAL route (most common):                     ║
║  Organisms from perineum → colonize external surface   ║
║  of catheter → migrate up to bladder                  ║
║                                                        ║
║  INTRALUMINAL route:                                   ║
║  Contamination of catheter junction or drainage bag    ║
║  → travel through lumen into bladder                   ║
║                                                        ║
║  BIOFILM formation on catheter surface:                ║
║  Organisms → attach → produce exopolysaccharide        ║
║  → BIOFILM (resistant to antibiotics + immune system)  ║
║  → Continuous source of infection                      ║
╚════════════════════════════════════════════════════════╝

• Often asymptomatic bacteriuria (ASB) - most common
• Symptomatic: Fever, suprapubic pain, cloudy/foul-smelling urine
• Severe: Pyelonephritis, bacteremia, sepsis

• Urine sample: Catheter specimen urine (not from bag)
• Dipstick: Nitrite positive (gram-negative), Leukocyte esterase positive
• Microscopy: >10 WBC/hpf, bacteria on Gram stain
• Culture: >10³ CFU/mL from catheter specimen (lower threshold than non-catheterized)
• Urine culture on CLED/MacConkey

• Insert catheter only when indicated (most important)
• Remove catheter as soon as possible (daily review)
• Strict aseptic technique during insertion
• Maintain closed drainage system
• Maintain urine flow (catheter below bladder level)
• Hand hygiene before/after catheter care
• Avoid routine antimicrobial prophylaxis

---

Q11. CLINICAL FEATURES OF TOXOPLASMA ENCEPHALITIS AND LAB DIAGNOSIS

• Obligate intracellular protozoan
• Definitive host: Cat (sexual cycle)
• Intermediate hosts: Humans, rodents, birds

Clinical Features of Toxoplasma Encephalitis (mainly in AIDS/immunocompromised):

╔══════════════════════════════════════════════════════════════════╗
║       CLINICAL FEATURES OF TOXOPLASMA ENCEPHALITIS              ║
║                                                                  ║
║  OCCURS MAINLY IN: AIDS patients (CD4 < 100 cells/μL)           ║
║  Mechanism: REACTIVATION of latent cysts (bradyzoites)          ║
║                                                                  ║
║  SUBACUTE ONSET (over days-weeks):                               ║
║  ├── HEADACHE (most common symptom)                              ║
║  ├── FEVER (low-grade)                                           ║
║  ├── FOCAL NEUROLOGICAL DEFICITS:                                ║
║  │   • Hemiparesis (most common focal sign)                      ║
║  │   • Aphasia                                                   ║
║  │   • Cerebellar ataxia                                         ║
║  │   • Cranial nerve palsies                                     ║
║  │   • Visual field defects                                      ║
║  ├── SEIZURES (30% of cases)                                     ║
║  ├── Confusion, altered mental status                            ║
║  └── Raised ICP: Papilledema, vomiting                           ║
║                                                                  ║
║  OCULAR TOXOPLASMOSIS (congenital OR reactivation):              ║
║  • Chorioretinitis (most common ocular manifestation)            ║
║  • Blurred vision, floaters, scotoma                             ║
║                                                                  ║
║  CONGENITAL TOXOPLASMOSIS:                                       ║
║  Classic triad:                                                  ║
║  1. Hydrocephalus                                                ║
║  2. Chorioretinitis                                              ║
║  3. Intracranial calcifications (periventricular)                ║
╚══════════════════════════════════════════════════════════════════╝

Lab Diagnosis of Toxoplasma Encephalitis:

• MRI (preferred): Multiple ring-enhancing lesions (with surrounding edema), typically at basal ganglia, thalamus, corticomedullary junction
• CT with contrast: Multiple hypodense lesions with ring enhancement ("target lesion" = central dot + ring = highly suggestive but not pathognomonic)
• Location: Basal ganglia (>70%), corticomedullary junction

• Lymphocytic pleocytosis (mild, 10-50 cells)
• Elevated protein
• Normal glucose
• T. gondii PCR from CSF: Sensitivity 50-60%, Specificity >95% - useful when positive
• Culture: Not routine (complex, dangerous)

• Anti-Toxoplasma IgG: >90% of AIDS patients with TE are seropositive
• Negative IgG → makes TE LESS likely (though not excluded)
• IgM: Usually negative in reactivation (not helpful in AIDS/TE)
• Rising IgG titres suggest acute primary infection

• Blood, CSF, BAL, tissue - highly specific
• Low sensitivity in CNS (50-60%) but confirms when positive

• Stereotactic biopsy
• H&E: Shows Toxoplasma tachyzoites (crescent/banana-shaped)
• IHC (immunohistochemistry): Confirms organism
• Only done when empirical treatment fails (10-14 days trial)

• Start Pyrimethamine + Sulfadiazine + Leucovorin
• If clinical + radiological improvement in 10-14 days → confirms TE
• Most centres diagnose by combination of serology + MRI + response to therapy

• Acute: Pyrimethamine 200mg loading then 50mg/day + Sulfadiazine 4-6g/day + Leucovorin 10-25mg/day x 6 weeks
• Maintenance (life-long if CD4 remains <200): Half-dose continuation
• Alternative: Pyrimethamine + Clindamycin (sulfa allergy)
• Prophylaxis: Cotrimoxazole (TMP-SMX) DS once daily when CD4 <100

---

Q12. ORGANISMS RESPONSIBLE FOR LRTI; LAB DIAGNOSIS OF PNEUMOCOCCAL PNEUMONIA

Organisms Causing LRTI (Lower Respiratory Tract Infection):

╔══════════════════════════════════════════════════════════════════╗
║        ORGANISMS CAUSING LRTI                                    ║
║                                                                  ║
║  BRONCHITIS (Acute):                                             ║
║  • Viral (most common): Rhinovirus, Influenza, RSV, Adenovirus   ║
║  • Bacterial: S. pneumoniae, H. influenzae, M. catarrhalis       ║
║                                                                  ║
║  COMMUNITY ACQUIRED PNEUMONIA (CAP):                             ║
║  Typical:                                                        ║
║  • Streptococcus pneumoniae (most common - "classical lobar")    ║
║  • Haemophilus influenzae (type b, elderly/COPD)                 ║
║  • Klebsiella pneumoniae (alcoholics, "currant jelly" sputum)    ║
║  • Staphylococcus aureus (post-influenza)                        ║
║  Atypical ("walking pneumonia"):                                 ║
║  • Mycoplasma pneumoniae (young adults, most common atypical)    ║
║  • Chlamydophila pneumoniae                                      ║
║  • Legionella pneumophila (Legionnaires' disease)                ║
║  Viral: Influenza, SARS-CoV-2                                    ║
║                                                                  ║
║  HOSPITAL ACQUIRED PNEUMONIA (HAP/VAP):                          ║
║  • Pseudomonas aeruginosa (most common in ICU)                   ║
║  • Acinetobacter baumannii (MDR, VAP)                            ║
║  • Klebsiella pneumoniae (ESBL)                                  ║
║  • MRSA                                                          ║
║                                                                  ║
║  IMMUNOCOMPROMISED / AIDS:                                       ║
║  • PCP (Pneumocystis jirovecii)                                  ║
║  • Aspergillus (invasive pulmonary aspergillosis)                ║
║  • CMV pneumonitis                                               ║
║  • Cryptococcus                                                  ║
║  • TB / MAC                                                      ║
╚══════════════════════════════════════════════════════════════════╝

---

Lab Diagnosis of PNEUMOCOCCAL PNEUMONIA:

SPECIMEN: Sputum (Gough first-morning deep cough), BAL,
          blood (blood culture), pleural fluid, urine (antigen)

╔══════════════════════════════════════════════════════════════════╗
║        LAB DIAGNOSIS OF PNEUMOCOCCAL PNEUMONIA                   ║
║                                                                  ║
║  1. SPUTUM GRAM STAIN:                                           ║
║     • Lancet-shaped gram-POSITIVE diplococci                     ║
║     • Surrounded by HALO (capsule - not stained)                 ║
║     • Many PMNs (neutrophils)                                    ║
║     • Mucoid background                                          ║
║     • Quality check: Bartlett's score / Murray-Washington:       ║
║       - <10 squamous cells + >25 PMNs/lpf = good sample          ║
║                                                                  ║
║  2. CULTURE (GOLD STANDARD):                                     ║
║     • Blood agar: α-hemolytic (green/partial hemolysis)          ║
║     • Colonies: Draughtsman/coin-like (umbilicated - central pit) ║
║     • CO2 atmosphere (5-10%), 35-37°C                            ║
║     • Blood culture: 2 sets - positive in 30-40% bacteremic cases║
║                                                                  ║
║  3. BIOCHEMICAL IDENTIFICATION:                                  ║
║     • Optochin (Ethylhydrocupreine) sensitivity: Zone ≥14mm      ║
║       = S. pneumoniae POSITIVE (viridans streptococci = resistant)║
║     • Bile solubility test: Colonies dissolve in 2% sodium       ║
║       deoxycholate = POSITIVE (specific for S. pneumoniae)       ║
║     • Inulin fermentation: Positive                               ║
║                                                                  ║
║  4. QUELLUNG REACTION (NEUFELD'S TEST):                          ║
║     • Mix sputum + type-specific anticapsular antibody +         ║
║       Methylene blue                                             ║
║     • Capsule SWELLS (appears to enlarge) = POSITIVE             ║
║     • GOLD STANDARD for serotyping (84 capsular serotypes)       ║
║                                                                  ║
║  5. URINE ANTIGEN TEST (BINAXNOW):                               ║
║     • Detects C-polysaccharide (cell wall antigen) in urine      ║
║     • Sensitivity 70-90%, Specificity 90-97%                     ║
║     • Rapid (15 min), useful even after antibiotics started      ║
║                                                                  ║
║  6. SEROLOGY:                                                    ║
║     • Anti-pneumococcal antibodies (not routinely used)          ║
║                                                                  ║
║  7. PCR: From sputum/blood - most sensitive                      ║
╚══════════════════════════════════════════════════════════════════╝

╔══════════════════════════════════════════════════════╗
║     S. PNEUMONIAE - GRAM STAIN                       ║
║                                                      ║
║  Purple (Gram +ve) background                        ║
║                                                      ║
║    ⟨⟩  ⟨⟩  ⟨⟩   ← Lancet-shaped                     ║
║    ⟨⟩          ← diplococci in pairs                 ║
║  [ HALO ]      ← capsule (clear space)               ║
║  [ PMN @ ]     ← neutrophils with bacteria           ║
║                                                      ║
║  PURPLE, LANCET-SHAPED DIPLOCOCCUS + CAPSULAR HALO   ║
╚══════════════════════════════════════════════════════╝

---

Q13. SHORT NOTE ON NON-GONOCOCCAL URETHRITIS (NGU)

Causes:

╔════════════════════════════════════════════════════════════╗
║           CAUSES OF NON-GONOCOCCAL URETHRITIS              ║
║                                                            ║
║  1. Chlamydia trachomatis (30-50%) - MOST COMMON           ║
║     Serovars D-K (genital serovars)                        ║
║                                                            ║
║  2. Ureaplasma urealyticum (10-20%)                        ║
║     Hydrolyses urea; sensitive to tetracyclines            ║
║                                                            ║
║  3. Mycoplasma genitalium (10-25%)                         ║
║     Emerging important cause; resistant to azithromycin    ║
║                                                            ║
║  4. Trichomonas vaginalis (5-10%)                          ║
║     Flagellate protozoan                                   ║
║                                                            ║
║  5. Herpes simplex virus (HSV-2) - less common             ║
║                                                            ║
║  6. Adenovirus (5-10%)                                     ║
║                                                            ║
║  7. Unknown cause (10-30%)                                 ║
╚════════════════════════════════════════════════════════════╝

• Mucopurulent/mucoid urethral discharge (less purulent than gonococcal)
• Dysuria (burning during micturition)
• Urethral itching
• Often asymptomatic (especially Chlamydia in women)
• Complications: Epididymitis, Reiter's syndrome (reactive arthritis), PID

• Obligate intracellular bacterium
• Two forms: Elementary body (infective, EB) ↔ Reticulate body (intracellular, dividing, RB)
• Cannot be grown on ordinary media (cell culture required)

• Chlamydia: Doxycycline 100mg BD x 7 days (DOC) OR Azithromycin 1g oral single dose
• Mycoplasma genitalium: Moxifloxacin 400mg OD x 7-14 days (azithromycin-resistant strains)
• Ureaplasma: Doxycycline / Azithromycin
• Treat sexual partner simultaneously

---

Q14. ORGANISMS CAUSING UTI; SPECIMEN COLLECTION IN UTI

Organisms Causing UTI:

╔══════════════════════════════════════════════════════════════════╗
║           ORGANISMS RESPONSIBLE FOR UTI                          ║
║                                                                  ║
║  COMMUNITY-ACQUIRED UTI (ascending, uncomplicated):              ║
║  1. Escherichia coli (75-85%) ← MOST COMMON                     ║
║     P-fimbriae (mannose-resistant), α-haemolysin                 ║
║  2. Klebsiella pneumoniae (5-10%)                                ║
║  3. Staphylococcus saprophyticus (5-15% in young women)          ║
║  4. Proteus mirabilis (urease → alkaline urine → struvite stones)║
║  5. Enterococcus faecalis (especially after instrumentation)     ║
║                                                                  ║
║  HOSPITAL-ACQUIRED / CATHETER UTI:                               ║
║  1. E. coli (still most common)                                  ║
║  2. Candida spp. (commonest fungal cause of CAUTI)               ║
║  3. Pseudomonas aeruginosa                                       ║
║  4. Klebsiella spp. (ESBL-producing)                             ║
║  5. Enterococcus                                                 ║
║  6. Serratia, Acinetobacter (MDR)                                ║
║                                                                  ║
║  SPECIAL UTI ORGANISMS:                                          ║
║  • Staphylococcus aureus UTI → suspect haematogenous spread      ║
║  • Mycobacterium tuberculosis → sterile pyuria (VERY IMPORTANT)  ║
║  • Schistosoma haematobium → haematuria + secondary infection    ║
║  • Adenovirus → haemorrhagic cystitis                            ║
╚══════════════════════════════════════════════════════════════════╝

---

Specimen Collection in UTI (IN DETAIL):

╔══════════════════════════════════════════════════════════════════╗
║         URINE SPECIMEN COLLECTION - STEP BY STEP                 ║
║                                                                  ║
║  A. MIDSTREAM CLEAN CATCH URINE (MSU) - Standard method:         ║
║                                                                  ║
║  TIMING: First morning specimen preferred                         ║
║           (concentrated; bacteria multiplied overnight)          ║
║                                                                  ║
║  PROCEDURE:                                                      ║
║  FEMALES:                                                        ║
║  1. Wash hands thoroughly                                        ║
║  2. Clean labia with soap-water or antiseptic wipe               ║
║     (front to back, one wipe = one stroke)                       ║
║  3. Hold labia apart during voiding                              ║
║  4. Discard FIRST 10-20 mL (flush urethra)                       ║
║  5. Collect MIDSTREAM 20-30 mL in STERILE WIDE-MOUTH container   ║
║  6. Cap immediately, label (name, time)                          ║
║                                                                  ║
║  MALES:                                                          ║
║  1. Retract foreskin (if uncircumcised)                          ║
║  2. Clean glans with moist swab                                  ║
║  3. Discard first 10-20 mL, collect mid-stream                   ║
║                                                                  ║
║  TRANSPORT:                                                      ║
║  • Process within 1 HOUR of collection (at room temperature)     ║
║  • Refrigerate at 4°C if delay (up to 24 hours)                  ║
║  • Boric acid tubes (grey cap): preserve at room temperature     ║
║    x 48 hours; add 3 mL of urine to tube                         ║
║                                                                  ║
║  B. CATHETER SPECIMEN URINE (CSU):                               ║
║  • Clean catheter port with alcohol swab                         ║
║  • Use sterile syringe and needle to aspirate from port          ║
║  • NEVER collect from the drainage bag                           ║
║                                                                  ║
║  C. SUPRAPUBIC ASPIRATION (SPA):                                 ║
║  • Gold standard (no contamination)                              ║
║  • Sterile needle directly into bladder through anterior wall    ║
║  • Used for: neonates, equivocal results, anaerobic culture      ║
║                                                                  ║
║  D. PAEDIATRIC COLLECTION:                                       ║
║  • Adhesive plastic bag over genitalia                           ║
║  • High contamination rate - repeat if positive                  ║
║  • SPA preferred in neonates                                     ║
╚══════════════════════════════════════════════════════════════════╝

---

Q15. NOTE ON CUTANEOUS LARVA MIGRANS (CLM)

• Ancylostoma braziliense (most common - cat/dog hookworm) - DOG HOOKWORM
• Ancylostoma caninum
• Uncinaria stenocephala
• (Humans are accidental hosts - larvae cannot complete development)

Pathogenesis:

╔══════════════════════════════════════════════════════════════════╗
║         PATHOGENESIS OF CUTANEOUS LARVA MIGRANS                  ║
║                                                                  ║
║  DOG/CAT defecates on soil → Eggs in faeces                      ║
║       ↓ (develop in warm, moist, sandy soil)                     ║
║  FILARIFORM (L3) LARVAE in soil                                  ║
║       ↓ (skin contact - walking barefoot, sunbathing)            ║
║  PENETRATION of human skin (especially feet, hands, buttocks)    ║
║       ↓ (humans = dead-end / accidental host)                    ║
║  Larva CANNOT find proper host receptors to go deeper            ║
║       ↓                                                          ║
║  Larva migrates HORIZONTALLY through epidermis                   ║
║  (few mm/day → few cm/day)                                       ║
║       ↓                                                          ║
║  SERPIGINOUS (snake-like) TRACK in skin                          ║
║  = CREEPING ERUPTION                                             ║
║  (intense eosinophilic inflammation + pruritus)                  ║
║       ↓                                                          ║
║  Eventually dies (self-limiting) in 4-8 weeks                    ║
╚══════════════════════════════════════════════════════════════════╝

Clinical Features:

• Intensely pruritic, serpiginous (winding/snake-like) track
• Erythematous, raised, vesicular/papular eruption
• Advances 1-2 cm/day
• Site: Feet, hands, buttocks (wherever skin contacts soil)
• Eosinophilia in blood
• Self-limiting (4-8 weeks if untreated)

DIAGRAM - CLM (Easy to draw):

╔══════════════════════════════════════════════════════╗
║     CUTANEOUS LARVA MIGRANS - SKIN DIAGRAM           ║
║                                                      ║
║  SKIN SURFACE:                                       ║
║  ─────────────────────────────────────────────────  ║
║     ~~~~~~~~~~~~~~~~~~~~→ ← Serpiginous track        ║
║      ~~~~~~~~~~~~~~~~~~   (red, raised, winding)     ║
║       ●~~~~~~~~~~~~~~~~~  ← Larva (at advancing end) ║
║  ─────────────────────────────────────────────────  ║
║  EPIDERMIS (larva confined here)                     ║
║  ─────────────────────────────────────────────────  ║
║  DERMIS                                              ║
║                                                      ║
║  Eosinophils around the track                        ║
╚══════════════════════════════════════════════════════╝

• Clinical diagnosis (characteristic appearance)
• Skin biopsy: Eosinophilic infiltrate; larva may be found (ahead of visible track, 1-2 cm)
• Blood: Peripheral eosinophilia
• No specific serological test

• Ivermectin 200 μg/kg single oral dose (DOC - most effective)
• Albendazole 400mg OD x 3 days (alternative, highly effective)
• Topical Thiabendazole (10-15% cream, applied 3x/day x 5-7 days) - for limited lesions
• Cryotherapy - NOT recommended (larva is ahead of the visible track)

---

Q16. LAB DIAGNOSIS OF GAS GANGRENE INFECTION

• Gas gangrene (Myonecrosis) - C. perfringens
• Tetanus - C. tetani
• Botulism - C. botulinum
• Food poisoning - C. perfringens Type A
• C. difficile colitis (AAD/PMC) - C. difficile

Morphology of C. perfringens:

╔══════════════════════════════════════════════════════════╗
║     C. PERFRINGENS - MORPHOLOGY                          ║
║                                                          ║
║  • Gram-positive, large, thick, box-car shaped bacilli  ║
║  • Anaerobic (obligate)                                  ║
║  • SPORES: Subterminal, oval (but spores RARELY seen     ║
║    in tissue - unlike other Clostridia)                  ║
║  • CAPSULE: Present (antiphagocytic)                     ║
║  • Motility: NON-MOTILE (unlike other Clostridia)        ║
║  • Toxins: Alpha toxin (phospholipase C) = MOST IMPORTANT║
╚══════════════════════════════════════════════════════════╝

Lab Diagnosis of Gas Gangrene:

╔══════════════════════════════════════════════════════════════════╗
║         LAB DIAGNOSIS OF GAS GANGRENE                            ║
║                                                                  ║
║  1. GRAM STAIN OF WOUND SMEAR (MOST IMPORTANT initial test):     ║
║     • Large gram-POSITIVE thick bacilli (box-car shape)          ║
║     • ABSENCE of PMNs (toxins destroy neutrophils)               ║
║     • ABSENCE of PMNs despite infection = highly characteristic  ║
║     • Background: necrotic tissue fragments                      ║
║                                                                  ║
║  2. CULTURE (ANAEROBIC - essential):                             ║
║     • Robertson's cooked meat (RCM) medium                       ║
║     • Thioglycollate broth                                       ║
║     • Blood agar in anaerobic jar (Gas-Pak system)               ║
║                                                                  ║
║  Blood agar - C. perfringens colonies:                           ║
║  • Double zone of hemolysis:                                     ║
║    INNER zone: complete (beta-hemolysis) - theta toxin           ║
║    OUTER zone: partial (alpha-hemolysis) - alpha toxin           ║
║  • "Stormy fermentation" in litmus milk broth:                   ║
║    Rapid clot formation + gas = "stormy clot" (PATHOGNOMONIC)    ║
║                                                                  ║
║  3. NAGLER REACTION:                                             ║
║     • Egg-yolk agar (lecithovitellin agar)                       ║
║     • Alpha toxin (lecithinase) cleaves lecithin in egg yolk     ║
║     → OPAQUE precipitate (pearly layer) around colonies          ║
║     → INHIBITED by specific anti-alpha-toxin antiserum           ║
║     = NAGLER REACTION POSITIVE                                   ║
║     • PATHOGNOMONIC of C. perfringens                            ║
║                                                                  ║
║  4. X-RAY / IMAGING:                                             ║
║     • Crepitus in tissue (gas) on plain X-ray                    ║
║     • MRI: Gas in muscle planes, necrosis                        ║
║                                                                  ║
║  5. TOXIN IDENTIFICATION:                                        ║
║     • ELISA for alpha-toxin                                      ║
║     • Reverse passive haemagglutination (RPHA)                   ║
║     • Mouse lethality test (historical)                          ║
║                                                                  ║
║  6. PCR: For toxin genes (cpa for alpha toxin)                   ║
╚══════════════════════════════════════════════════════════════════╝

╔══════════════════════════════════════════════════════╗
║     NAGLER REACTION (Egg-yolk agar)                  ║
║                                                      ║
║  LEFT HALF (no antiserum):  RIGHT HALF (+ antiserum):║
║  ┌─────────────────┐        ┌─────────────────┐      ║
║  │  Colony         │        │  Colony         │      ║
║  │  ◐◐◐◐◐◐        │        │  (no opacity)   │      ║
║  │ OPAQUE ZONE     │        │   INHIBITED     │      ║
║  │ (positive)      │        │                 │      ║
║  └─────────────────┘        └─────────────────┘      ║
╚══════════════════════════════════════════════════════╝

1. Surgical debridement (MOST IMPORTANT) - wide excision of all necrotic tissue, amputation if needed
2. Penicillin G IV high dose (DOC) + Metronidazole OR Clindamycin
3. Hyperbaric Oxygen (HBO): Anaerobic organism inhibited by high O2; adjunct therapy
4. Polyvalent antitoxin (limited evidence)

---

Q17. DIFFERENCE BETWEEN HSV-1 AND HSV-2

╔══════════════════════════════════════════════════════════════════════╗
║              HSV-1 vs HSV-2 - COMPARISON TABLE                       ║
╠══════════════════════╦═══════════════════════╦════════════════════════╣
║ Feature              ║ HSV-1                 ║ HSV-2                  ║
╠══════════════════════╬═══════════════════════╬════════════════════════╣
║ Common name          ║ Oral herpes           ║ Genital herpes          ║
║ Primary site         ║ Oropharynx (lips,     ║ Genitalia, buttocks,   ║
║                      ║ gingiva)              ║ thighs                 ║
║ Transmission         ║ Saliva, droplets,     ║ Sexual contact,        ║
║                      ║ direct contact        ║ vertical               ║
║ Latency site         ║ Trigeminal ganglion   ║ Sacral dorsal root     ║
║                      ║ (CN V)                ║ ganglia (S2-S5)        ║
║ Reactivation trigger ║ UV light, fever,      ║ Stress, menstruation,  ║
║                      ║ stress, fever         ║ immunosuppression      ║
║ Recurrent lesions    ║ Herpes labialis       ║ Genital recurrences    ║
║                      ║ (cold sores)          ║ (more frequent)        ║
║ Meningitis           ║ HSE (Herpes           ║ Aseptic meningitis     ║
║                      ║ Simplex Encephalitis) ║ (Mollaret's meningitis)║
║                      ║ - temporal lobe, FATAL║                        ║
║ Keratoconjunctivitis ║ YES (common)          ║ Rare                   ║
║ Neonatal herpes      ║ Less common           ║ More common (birth     ║
║                      ║                       ║ canal exposure)        ║
║ Carcinoma assoc.     ║ Oral/oropharyngeal    ║ Cervical carcinoma     ║
║                      ║ (co-factor with HPV)  ║ (co-factor)            ║
║ Lab differentiation  ║ Cytopathic effect;    ║ PCR (most reliable)    ║
║                      ║ Type-specific ELISA   ║ Type-specific IgG      ║
║ Treatment            ║ Acyclovir (topical    ║ Valacyclovir oral      ║
║                      ║ or oral)              ║ (episodic/suppressive) ║
╚══════════════════════╩═══════════════════════╩════════════════════════╝

• Family: Herpesviridae; Large dsDNA virus; Enveloped
• ICOSAHEDRAL capsid; Tegument layer between capsid and envelope
• Establish latency in sensory ganglia
• Reactivate during immunosuppression
• Cytopathic effect: Intranuclear inclusions (Cowdry type A - eosinophilic)
• Tzanck smear: Multinucleated giant cells (both types)
• Treatment: Acyclovir / Valacyclovir / Famciclovir (all require viral thymidine kinase for activation)

---

Q18. BRIEF NOTE ON PCP PNEUMONIA IN HIV INDIVIDUALS

• Formerly thought to be protozoan; reclassified as FUNGUS (Ascomycota) based on rRNA and wall biochemistry
• Cannot be cultured in vitro
• AIDS-defining illness when CD4 <200 cells/μL

Morphology:

• Trophozoites: Small, 1-4 μm, pleomorphic
• Cysts (Asci): 5-8 μm, spherical, contain 8 intracystic bodies (ascospores)
• Pneumocysts: Cysts with 8 intracystic bodies

Clinical Features (HIV/AIDS, CD4 typically <200):

╔══════════════════════════════════════════════════════════════╗
║       CLINICAL FEATURES OF PCP IN HIV                        ║
║                                                              ║
║  INSIDIOUS ONSET (weeks):                                    ║
║  ├── Progressive exertional dyspnoea (most common)           ║
║  ├── Dry, non-productive COUGH                               ║
║  ├── LOW-GRADE FEVER                                         ║
║  ├── Fatigue, weight loss                                    ║
║  └── NORMAL BREATH SOUNDS or fine bibasal crackles           ║
║                                                              ║
║  INVESTIGATIONS:                                             ║
║  • SpO2 drops with exercise (HALLMARK)                       ║
║  • LDH elevated (>500 IU/L = bad prognosis)                  ║
║  • CXR: Bilateral, diffuse, INTERSTITIAL pattern             ║
║    "Ground-glass" or "bat-wing" opacities                    ║
║  • HRCT: Bilateral ground-glass attenuation                  ║
║  • PaO2 < 70 mmHg = severe (needs adjunct steroids)          ║
╚══════════════════════════════════════════════════════════════╝

Lab Diagnosis:

GMS STAIN DIAGRAM (exam-friendly):
╔══════════════════════════════════════════════════╗
║   PCP CYSTS on GMS stain                         ║
║                                                  ║
║  Green/brown background                          ║
║     ◯  ◯  ◯  ← Black cysts (cup-shaped or       ║
║   ◯   ◯   ◯    boat-shaped with "dot" =          ║
║     ◯  ◯       intracystic body)                 ║
║  5-8 μm cysts, 8 intracystic bodies              ║
║  Seen in ALVEOLAR EXUDATE (foamy)                ║
╚══════════════════════════════════════════════════╝

• TMP-SMX (Co-trimoxazole) = DRUG OF CHOICE
  • Mild-moderate: TMP 15-20mg/kg + SMX 75-100mg/kg/day oral x 21 days
  • Severe (PaO2 <70mmHg): IV co-trimoxazole + Prednisolone 40mg BD x 5 days (then taper)
• Alternatives: Pentamidine IV, Dapsone + TMP, Clindamycin + Primaquine

• Co-trimoxazole DS 1 tablet OD (also prophylaxis for Toxoplasma)
• Discontinue when CD4 >200 sustained for 3 months on ART

---

Q19. ENUMERATE DERMATOPHYTE INFECTIONS AND LAB DIAGNOSIS

Dermatophytes (Ringworm fungi):

• Trichophyton - skin, hair, nails (most species)
• Microsporum - skin and hair (NOT nails)
• Epidermophyton - skin and nails (NOT hair)

Classification of Dermatophytoses (TINEA):

╔══════════════════════════════════════════════════════════════════╗
║           DERMATOPHYTE INFECTIONS - CLASSIFICATION               ║
║                                                                  ║
║  TINEA (Ringworm):                                               ║
║  ┌─────────────────────────────────────────────────────────┐     ║
║  │ DISEASE          │ SITE          │ COMMON ORGANISM       │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea capitis    │ Scalp         │ Trichophyton tonsurans│     ║
║  │ (ringworm scalp) │               │ Microsporum canis     │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea corporis   │ Body skin     │ T. rubrum, M. canis   │     ║
║  │ (ringworm body)  │               │                       │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea cruris     │ Groin         │ T. rubrum             │     ║
║  │ (jock itch)      │ (perineum)    │ E. floccosum          │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea pedis      │ Feet          │ T. rubrum (most       │     ║
║  │ (athlete's foot) │               │  common worldwide)    │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea unguium    │ Nails         │ T. rubrum             │     ║
║  │ (Onychomycosis)  │               │                       │     ║
║  ├─────────────────────────────────────────────────────────┤     ║
║  │ Tinea barbae     │ Beard         │ T. violaceum          │     ║
║  │ Tinea faciei     │ Face          │ T. mentagrophytes     │     ║
║  └─────────────────────────────────────────────────────────┘     ║
║                                                                  ║
║  EPIDEMIOLOGICAL CLASSIFICATION:                                 ║
║  • Zoophilic: From animals (M. canis from cats/dogs)             ║
║  • Anthropophilic: Human-to-human (T. rubrum, T. tonsurans)      ║
║  • Geophilic: From soil (M. gypseum)                             ║
╚══════════════════════════════════════════════════════════════════╝

Lab Diagnosis of Dermatophytoses:

• Skin: Scrapings from active edge of lesion (not center which is healed)
• Hair: Infected hair stubs + kerion material (pull with forceps - fluorescent hair under UV)
• Nails: Nail clippings + subungual debris (deep scrapings)

╔══════════════════════════════════════════════════════════════════╗
║         LAB DIAGNOSIS OF DERMATOPHYTES                           ║
║                                                                  ║
║  1. WOOD'S LAMP (UV light, 365 nm):                              ║
║     • SCREENING for scalp ringworm (Tinea capitis)               ║
║     • Microsporum species → BRIGHT GREEN/YELLOW-GREEN            ║
║       fluorescence (due to pteridine in hair shaft)              ║
║     • Trichophyton → NO fluorescence (exception: T. schoenleinii)║
║     • Quick in-office screening                                  ║
║                                                                  ║
║  2. KOH MOUNT (10-20% KOH - key diagnostic test):                ║
║     • Dissolves keratin → reveals fungal elements                ║
║     • Skin scraping + 1-2 drops 20% KOH on glass slide          ║
║     • Gently heat → wait 15-20 min                               ║
║     • POSITIVE: Branching, septate hyphae (skin/nails)           ║
║               Arthrospores within/around hair shaft (endothrix/  ║
║               ectothrix - Tinea capitis)                         ║
║                                                                  ║
║  HAIR INVASION PATTERNS (Tinea capitis):                         ║
║  ├── ECTOTHRIX: Arthroconidia on OUTSIDE hair shaft              ║
║  │   (Microsporum, T. mentagrophytes)                            ║
║  └── ENDOTHRIX: Arthroconidia INSIDE hair shaft                  ║
║      (T. tonsurans, T. violaceum) - "black dot" tinea            ║
║      → Hair breaks within follicle → black dot on scalp          ║
║                                                                  ║
║  3. CULTURE (SDA):                                               ║
║     • SDA with chloramphenicol + cycloheximide                   ║
║       (DTM - Dermatophyte Test Medium: colour change red)        ║
║     • Incubate at 25-28°C for 1-4 weeks                          ║
║     • Identify by: Colony morphology + LPCB mount                ║
║                                                                  ║
║  LPCB MOUNT (Lactophenol Cotton Blue):                           ║
║  • T. rubrum: Pencil-shaped macroconidia (rare); microconidia    ║
║  • T. mentagrophytes: Spiral hyphae, grape-like microconidia     ║
║  • Microsporum: Spindle-shaped macroconidia with thick walls     ║
║  • Epidermophyton: Beaver-tail shaped macroconidia (no micro)    ║
║                                                                  ║
║  4. FLUORESCENCE MICROSCOPY (Calcoflour white + KOH):            ║
║     Most sensitive for detecting hyphae in specimens             ║
╚══════════════════════════════════════════════════════════════════╝

• Topical: Clotrimazole, Miconazole, Terbinafine, Ketoconazole cream
• Systemic (scalp/nail/extensive): Griseofulvin (Tinea capitis, especially Microsporum - binds keratin); Terbinafine (Tinea unguium/nails - DOC); Itraconazole

---

Q20. NEUROCYSTICERCOSIS - PATHOGENESIS, DIAGNOSIS, CLINICAL FEATURES, CNS DIAGNOSTIC TOOLS

• Ingestion of T. solium EGGS (not cysticerci) via contaminated food/water
• Autoinfection: Reverse peristalsis/vomiting brings gravid proglottids to stomach

Pathogenesis:

╔══════════════════════════════════════════════════════════════════╗
║         PATHOGENESIS OF NEUROCYSTICERCOSIS                       ║
║                                                                  ║
║  T. solium EGGS ingested                                         ║
║       ↓ Gastric acid → oncospheres released                      ║
║  ONCOSPHERES penetrate gut wall                                  ║
║       ↓ Blood + lymphatics                                       ║
║  Reach BRAIN (most common site of extraintestinal cysticercosis) ║
║       ↓                                                          ║
║  CYSTICERCUS CELLULOSAE develops in brain parenchyma             ║
║  (also subarachnoid space, ventricles, spinal cord)              ║
║       ↓                                                          ║
║  STAGES:                                                         ║
║  1. Vesicular: Live cyst, minimal inflammation; ASYMPTOMATIC     ║
║  2. Colloidal vesicular: Cyst begins to degenerate; WBC attracted║
║     Inflammation, edema → SEIZURES, HEADACHE                    ║
║  3. Granular nodular: Calcifying; fibrosis                       ║
║  4. Calcified nodular: Dead calcified cyst; may still cause      ║
║     seizures (calcification triggers inflammation)               ║
╚══════════════════════════════════════════════════════════════════╝

Clinical Features:

Diagnosis - CNS Diagnostic Tools:

CT SCAN:
• Hypodense cysts with eccentric scolex ("hole with dot" sign)
• Multiple ring-enhancing lesions (dying cysts)
• Calcified lesions (dead cysts)
• Hydrocephalus
• Perilesional edema

MRI (BEST for NCC):
• T1: Cyst isointense/hypointense to CSF; scolex (dot) = hyperintense
• T2: Fluid-filled cysts hyperintense (like CSF)
• FLAIR: Perilesional edema = hyperintense
• DWI: Abscesses (r/o) - NCC cysts do NOT restrict diffusion
• Detects: Live cysts, scolex, calcified cysts, intraventricular cysts

• Eosinophilic pleocytosis (pathognomonic when present)
• Elevated protein
• Low glucose
• CSF ELISA: Anti-cysticercal IgG antibodies
• CSF PCR: Highly specific

• EITB (Enzyme-Linked Immunoelectrotransfer Blot) - gold standard serological test; sensitivity 94-98% in multiple cysts
• ELISA: IgG anti-cysticercal antibodies
• Note: Single calcified lesion may be seronegative

• Cysticercus structure: Bladder (fluid-filled) + invaginated scolex (with 4 suckers + rostellum with hooks)
• Diagnosis confirmatory

• Albendazole 15mg/kg/day x 8-28 days (DOC - kills live cysts)
• Praziquantel (alternative)
• Dexamethasone/Prednisolone - add to reduce perilesional edema during therapy
• Anticonvulsants (AED) - Phenytoin, Carbamazepine (for seizures)
• Calcified cysts: No antiparasitic needed; manage seizures only
• Intraventricular cysts: Endoscopic removal
• Hydrocephalus: VP shunt

---

Q21. LAB DIAGNOSIS OF BACTERIAL UTI

Microscopy:

╔══════════════════════════════════════════════════════════════════╗
║         LAB DIAGNOSIS - BACTERIAL UTI                            ║
║                                                                  ║
║  SPECIMEN: MSU (Midstream clean catch urine)                     ║
║                                                                  ║
║  STEP 1: URINALYSIS (Dipstick)                                   ║
║  ├── Nitrite: Positive → gram -ve bacteria (reduce nitrate)      ║
║  ├── Leukocyte esterase: Positive → pyuria (WBCs present)        ║
║  ├── Blood: May be positive (haemorrhagic cystitis)              ║
║  └── Protein: Mild elevation                                     ║
║                                                                  ║
║  STEP 2: MICROSCOPY (Uncentrifuged urine)                        ║
║  ├── WBCs: >10 cells/mm³ = pyuria                                ║
║  ├── RBCs: >5 cells/mm³ = haematuria                             ║
║  ├── Bacteria: Presence of ANY bacteria                          ║
║  ├── Casts: WBC casts → pyelonephritis/renal infection           ║
║  └── Epithelial cells: >5 squamous cells → contaminated sample   ║
║                                                                  ║
║  STEP 3: GRAM STAIN (uncentrifuged urine)                        ║
║  ├── 1+ bacterium/oil immersion field = 10⁵ CFU/mL              ║
║  ├── Gram -ve rods (E. coli, Klebsiella, Pseudomonas)            ║
║  ├── Gram +ve cocci clusters (Staph)                             ║
║  └── Gram +ve cocci in chains (Enterococcus)                     ║
║                                                                  ║
║  STEP 4: CULTURE (KEY STEP)                                      ║
║  Media: CLED agar (Cystine Lactose Electrolyte Deficient)        ║
║         MacConkey agar                                           ║
║         Blood agar                                               ║
║  Method: CALIBRATED LOOP (0.001 mL or 0.01 mL)                  ║
║                                                                  ║
║  SIGNIFICANT BACTERIURIA THRESHOLD:                              ║
║  • MSU (symptomatic female): ≥10³ CFU/mL                         ║
║  • MSU (symptomatic male): ≥10³ CFU/mL                           ║
║  • Asymptomatic bacteriuria (screening): ≥10⁵ CFU/mL in 2 MSUs  ║
║  • Catheter specimen: ≥10³ CFU/mL                                ║
║  • Suprapubic aspiration: ANY growth significant                 ║
║                                                                  ║
║  STEP 5: IDENTIFICATION + SENSITIVITY                            ║
║  ├── Biochemical tests (IMVIC for E. coli)                       ║
║  ├── Oxidase test (Pseudomonas = positive)                       ║
║  ├── API 20E / MALDI-TOF (rapid ID)                              ║
║  └── AST: Kirby-Bauer disk diffusion / MIC (VITEK)               ║
╚══════════════════════════════════════════════════════════════════╝

• E. coli: Yellow, opaque (lactose fermenter)
• Klebsiella: Mucoid, yellow (lactose fermenter)
• Pseudomonas: Blue-green, non-lactose fermenter
• Proteus: Translucent, non-lactose fermenter

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Q22. WELL-LABELLED DIAGRAM OF RABIES VIRUS AND PEP

Rabies Virus Diagram:

╔══════════════════════════════════════════════════════════════════╗
║         RABIES VIRUS - WELL LABELLED DIAGRAM                     ║
║                                                                  ║
║         ←────── 180 nm ──────→                                   ║
║         ┌──────────────────────┐                                 ║
║         │ ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ │ ← Glycoprotein (G) spikes       ║
║  FLAT   │ ████████████████████ │ ← LIPID ENVELOPE                ║
║  END    │ ─────────────────── │ ← MATRIX (M) protein            ║
║  ←──→   │ ╔═══╗ ╔═══╗ ╔═══╗  │                                  ║
║         │ ║RNA║═║ N ║═║L/P║  │ ← RNP (ssRNA + N + L + P)       ║
║         │ ╚═══╝ ╚═══╝ ╚═══╝  │                                  ║
║         │ ─────────────────── │ ← MATRIX (M) protein            ║
║         │ ████████████████████ │ ← LIPID ENVELOPE                ║
║         │ ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ │ ← G-protein spikes              ║
║         └──────────────────────┘                                 ║
║                               → ROUNDED END                      ║
║                                                                  ║
║  KEY:                                                            ║
║  • Shape: BULLET/BACILLIFORM (180×75 nm)                         ║
║  • Genome: ssRNA, negative sense, non-segmented                  ║
║  • Nucleocapsid: Helical symmetry                                ║
║  • G protein: Induces virus-neutralizing antibodies              ║
║               Responsible for attachment to nAchR and P75NTR    ║
║  • N protein: Forms Negri bodies in infected neurons             ║
╚══════════════════════════════════════════════════════════════════╝

PEP (Post-Exposure Prophylaxis) Chart:

╔══════════════════════════════════════════════════════════════════╗
║         RABIES PEP - COMPLETE PROTOCOL                           ║
║                                                                  ║
║  STEP 1: WOUND MANAGEMENT (IMMEDIATE - MOST IMPORTANT)           ║
║  ├── Wash wound with soap + water x 15 min                       ║
║  ├── Apply 70% alcohol/povidone-iodine                           ║
║  ├── Do NOT suture (if must suture, do it late, loosely)         ║
║  └── Tetanus prophylaxis if needed                               ║
║                                                                  ║
║  STEP 2: WHO CATEGORY ASSESSMENT                                 ║
║  ├── Cat I (touch/lick intact skin): Wash only, NO PEP           ║
║  ├── Cat II (minor scratch, no bleeding): Vaccine series         ║
║  └── Cat III (deep bite/bleed/mucosa): Vaccine + RIG             ║
║                                                                  ║
║  STEP 3: VACCINE (Essen 5-dose IM schedule):                     ║
║  Day 0 → Day 3 → Day 7 → Day 14 → Day 28                        ║
║  (IM deltoid; cell culture vaccine: PCECV/PVRV/HDCV)            ║
║                                                                  ║
║  STEP 4: RIG (ONLY Cat III, given on Day 0 ONLY):                ║
║  ├── HRIG (Human): 20 IU/kg                                      ║
║  └── ERIG (Equine): 40 IU/kg (after sensitivity testing)         ║
║  → Infiltrate maximum at wound site                               ║
║  → Remaining IM at distant site from vaccine                     ║
║                                                                  ║
║  FOR PREVIOUSLY VACCINATED (PrEP done):                          ║
║  → 2 doses ONLY: Day 0 + Day 3 (NO RIG needed)                  ║
║                                                                  ║
║  INTRADERMAL (ID) 2-site schedule (economical, India):           ║
║  Day 0 (2 sites) → Day 3 (2 sites) → Day 7 (2 sites) →          ║
║  Day 28 (1 site) → Day 90 (1 site)                               ║
╚══════════════════════════════════════════════════════════════════╝

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Q23. DEFINE PRECIPITATION AND APPLICATIONS WITH EXAMPLES

• Antigen must be SOLUBLE (not particulate → that's agglutination)
• Optimal proportions (zone of equivalence): Neither antigen nor antibody in excess
• Electrolytes (NaCl, physiological saline) needed

Zone Phenomenon (Lattice theory):

╔══════════════════════════════════════════════════════════════════╗
║           LATTICE THEORY / ZONE PHENOMENON                       ║
║                                                                  ║
║  ANTIBODY          ZONE OF            ANTIGEN                    ║
║  EXCESS            EQUIVALENCE        EXCESS                     ║
║  ┌─────────┐      ┌─────────────┐    ┌─────────┐                ║
║  │ Small   │      │ MAXIMUM     │    │ Small   │                ║
║  │ lattice │      │ PRECIPITATE │    │ lattice │                ║
║  │ = small │      │ (OPTIMAL)   │    │ = small │                ║
║  │precipit.│      │             │    │precipit.│                ║
║  └─────────┘      └─────────────┘    └─────────┘                ║
║  (prozone)         (equivalence)     (postzone)                  ║
║                                                                  ║
║  PROZONE: Ab excess → small, soluble lattice → NO precipitate    ║
║  POSTZONE: Ag excess → small, soluble lattice → NO precipitate   ║
║  ZONE OF EQUIVALENCE: MAXIMUM large lattice = MAX precipitate    ║
╚══════════════════════════════════════════════════════════════════╝

Types of Precipitation Reactions (with Applications & Examples):

╔══════════════════════════════════════════════════════════════════╗
║         TYPES OF PRECIPITATION REACTIONS                         ║
║                                                                  ║
║  1. PRECIPITATION IN LIQUIDS:                                    ║
║     a. RING (Interfacial) TEST (Ascoli's test):                  ║
║        • Antigen layered over antibody in narrow tube            ║
║        • Precipitate forms at interface as RING                  ║
║        • Application: Diagnosis of ANTHRAX                       ║
║          (Ascoli's thermoprecipitin test for anthrax in hides)   ║
║                                                                  ║
║  2. PRECIPITATION IN GEL (Agar/Agarose):                         ║
║                                                                  ║
║     a. DOUBLE IMMUNODIFFUSION (Ouchterlony method):              ║
║        • Both Ag and Ab diffuse toward each other in agar        ║
║        • Precipitin line forms where they meet                   ║
║        • Applications:                                           ║
║          ✓ Detect M and H bands in Histoplasmosis                ║
║          ✓ Identify fungal species (Aspergillus precipitins)     ║
║          ✓ Characterize antigen-antibody identity/cross-react.   ║
║                                                                  ║
║     b. SINGLE RADIAL IMMUNODIFFUSION (SRID - Mancini):           ║
║        • Ab in agar, Ag in well                                  ║
║        • Area of precipitin ring ∝ Ag concentration             ║
║        • Application: QUANTIFY immunoglobulins (IgG, IgA, IgM)  ║
║                        Complement components (C3, C4)            ║
║                                                                  ║
║     c. IMMUNOELECTROPHORESIS (IEP):                              ║
║        • Ag separated by electrophoresis first, then             ║
║          antibody diffuses from trough                           ║
║        • Application: Identify myeloma proteins (paraproteins)   ║
║                                                                  ║
║     d. COUNTER CURRENT IMMUNOELECTROPHORESIS (CCIE):             ║
║        • Both Ag and Ab move toward each other under current     ║
║        • RAPID and MORE SENSITIVE than Ouchterlony               ║
║        • Application: Bacterial antigens in CSF/serum            ║
║          (meningococcus, H. influenzae, S. pneumoniae)           ║
║          Anti-dsDNA in SLE, CIE in Leptospirosis                 ║
║                                                                  ║
║  3. IMMUNOTURBIDIMETRY / IMMUNONEPHELOMETRY:                     ║
║     • Ag-Ab complex = turbidity measured by light scattering     ║
║     • Application: Quantify CRP, IgG, IgA, IgM, complement      ║
║       in clinical labs (automated analyzers)                     ║
╚══════════════════════════════════════════════════════════════════╝

Summary Table:

• False negative result due to ANTIBODY EXCESS in undiluted serum
• Example: VDRL test in secondary syphilis (very high antibody titre → prozone → false negative → dilute serum to get positive result)
• Solution: Test serum at multiple dilutions

---

References: Apurba Shastri's Textbook of Microbiology (4th Ed); Jawetz Melnick & Adelberg 28th Ed; Murray's Medical Microbiology 9th Ed; WHO Rabies Guidelines; India NIP/NVBDCP schedules; NACO guidelines.

MUHS Exam Tip: For 5-mark SAQs, ideal structure = Definition (1 mark) + Classification or Pathogenesis (2 marks) + Diagram/Table (1 mark) + Lab diagnosis or Treatment (1 mark). For 8-10 mark LAQs, each sub-part gets 2-3 marks. Time: 2 min per mark = 16-20 min for a 10-mark LAQ.