Got all questions. Now answering all of them comprehensively: --- # MICROBIOLOGY PAPER II - COMPLETE ANSWERS ## (Apurva Shastri - Professional Exam) --- # IMMUNOLOGY ## INFECTION ### SN 1. Define: Carrier, Contact Carrier, Paradoxical Carrier, Convalescent Carrier **i) Carrier:** A person who harbors the pathogenic microorganism without showing overt clinical signs of disease, yet is capable of transmitting the infection to others. They serve as a reservoir of infection. **ii) Contact Carrier (Healthy Carrier):** A person who harbors the pathogen without ever having suffered from the disease. They acquire the organism through contact with a case/carrier but remain asymptomatic throughout. Example: Carriers of N. meningitidis in the nasopharynx (up to 10-15% of population), healthy carriers of S. typhi. **iii) Paradoxical Carrier:** A person who acquires the infection from a carrier, rather than from a clinical case of the disease. The source of infection is a carrier (not an overt case) - this is "paradoxical" because the carrier (who is not ill) infects another person. Example: A person who becomes a typhoid carrier after contact with another carrier. **iv) Convalescent Carrier:** A person who has recovered clinically from the disease but continues to harbor and shed the pathogen for a variable period. Example: Typhoid Mary (S. typhi in gallbladder), convalescent diphtheria carriers, S. typhi after enteric fever (chronic carrier if >1 year). --- ## IMMUNITY ### SN 1. Innate Immunity - Mechanisms **Definition:** Non-specific, inborn resistance to infection; present from birth; does not require prior exposure to antigen; acts immediately. **Mechanisms of Innate Immunity:** **1. Physical/Anatomical Barriers:** - Intact skin (keratin layer) - impermeable to most organisms - Mucous membranes - trap organisms in mucus - Mucociliary escalator (respiratory tract) - sweeps organisms upward - Cough, sneeze reflexes - Flushing action of urine, tears, saliva **2. Physiological/Biochemical Barriers:** - **pH:** Gastric acid (pH 2) kills most ingested organisms; acid vaginal pH - **Lysozyme:** In tears, saliva, nasal secretions - cleaves NAM-NAG bonds in bacterial cell wall - **Lactoferrin:** Binds iron - bacteriostatic (deprives bacteria of iron) - **Defensins:** Antimicrobial peptides in neutrophil granules and epithelial cells - **Complement (alternative pathway):** Activated directly by bacterial surfaces - **Interferons (IFN-α, IFN-β):** Released by virus-infected cells - induce antiviral state in neighboring cells - **Acute phase proteins:** CRP, serum amyloid A, mannan-binding lectin (MBL) - opsonize bacteria - **Temperature:** Fever inhibits many pathogens; cold areas (skin surface 34°C) restrict some fungi **3. Cellular Mechanisms:** - **Phagocytes:** - Neutrophils (PMNs) - first responders; phagocytose and kill bacteria via oxidative burst (H2O2, superoxide, hypochlorite) and granule enzymes (myeloperoxidase, elastase, lactoferrin) - Macrophages - tissue phagocytes; long-lived; process antigens; release cytokines (TNF, IL-1, IL-6, IL-12) - Dendritic cells - bridge innate and adaptive immunity; professional antigen-presenting cells - **Natural Killer (NK) cells:** Lymphocytes that kill virus-infected cells and tumor cells without prior sensitization; recognize absence of MHC class I ("missing self") - **Mast cells, Basophils, Eosinophils:** Innate effectors in allergy and parasitic infections **4. Pattern Recognition Receptors (PRRs):** - **Toll-Like Receptors (TLRs):** Recognize PAMPs (Pathogen-Associated Molecular Patterns) - TLR4 recognizes LPS (Gram-negative endotoxin) - TLR9 recognizes bacterial/viral DNA (CpG motifs) - TLR3 recognizes double-stranded RNA (viral) - **NOD receptors, RIG-I:** Intracellular innate sensors --- ## ANTIBODY - IMMUNOGLOBULIN ### SN 1. IgG - Structure and Function **Structure of IgG:** - **Basic immunoglobulin structure:** Two heavy chains (γ-chains) + two light chains (κ or λ), linked by disulfide bonds - **MW:** ~150,000 Daltons (7S) - **Domains:** Each heavy chain has 1 VH + 3 CH domains (CH1, CH2, CH3); each light chain has VL + CL - **Fab fragment** (Fragment antigen-binding): VH + VL + CH1 + CL - contains antigen-binding site - **Fc fragment** (Fragment crystallizable): CH2 + CH3 - mediates effector functions (complement activation, FcR binding) - **Hinge region:** Flexible region between CH1 and CH2 - allows Fab arm movement - **Papain** cleaves at hinge → 2 Fab + 1 Fc - **Pepsin** cleaves below hinge → F(ab')2 + pFc' - **Subclasses:** IgG1, IgG2, IgG3, IgG4 (differ in hinge length, complement activation) **Functions of IgG:** 1. **Most abundant** serum immunoglobulin (75-80% of total Ig) 2. **Opsonization:** Fc region binds Fc-γR on phagocytes → enhanced phagocytosis 3. **Complement activation** (classical pathway) via CH2 domain (IgG1, IgG2, IgG3) 4. **Neutralization** of toxins and viruses 5. **ADCC** (Antibody-Dependent Cell-Mediated Cytotoxicity) via NK cells 6. **Placental transfer** (only Ig that crosses placenta via FcRn) - provides passive immunity to neonate 7. **Secondary immune response** - main antibody produced in secondary/anamnestic response 8. **Long half-life:** ~23 days (longest of all Ig) --- ### SN 2. IgM - Properties / Functions / Structure **Structure of IgM:** - **Pentamer:** 5 basic immunoglobulin units (each: 2 heavy μ-chains + 2 light chains) joined by **J-chain** (joining chain) and disulfide bonds - **MW:** ~900,000 Daltons (19S) - **10 antigen-binding sites** (Fab fragments) - highest valency - **J-chain:** Glycoprotein that polymerizes the pentamer; also found in IgA **Properties of IgM (enumerate):** 1. First antibody produced in primary immune response (earliest marker of recent infection) 2. Largest immunoglobulin (pentameric, 19S, 900 kDa) 3. Confined to intravascular space (does NOT cross placenta or enter tissue fluids easily due to large size) 4. Most efficient complement activator (classical pathway - single molecule can activate C1q) 5. Best agglutinating antibody (10 binding sites - high valency) 6. Half-life: ~5 days (short) 7. Present on B-cell surface as monomer (BCR) 8. Important in early defense against bacteremia **Functions:** - Primary response antibody (IgM → IgG class switching) - Agglutination of bacteria, RBCs (blood group antibodies ABO are IgM) - Complement activation (most efficient) - Opsonization - Isohemagglutinins (anti-A, anti-B) are IgM --- ### SN 3. Define/Classify Antibodies **Definition:** Antibodies (Immunoglobulins) are glycoprotein molecules produced by plasma cells (differentiated B lymphocytes) in response to antigenic stimulation, capable of specifically binding to the antigen that induced their formation. **Classification:** **By class (isotype) - 5 classes based on heavy chain type:** 1. IgG (γ chain) - 4 subclasses 2. IgA (α chain) - 2 subclasses 3. IgM (μ chain) 4. IgD (δ chain) 5. IgE (ε chain) **By specificity:** - Monoclonal (single clone, single specificity) vs. Polyclonal **By origin:** - Natural (isohemagglutinins) vs. Immune (after exposure) **By function:** - Agglutinins, precipitins, opsonins, antitoxins, neutralizing antibodies, complement-fixing antibodies --- ### SN 4. IgA - Diagram Description **Serum IgA:** Monomer (MW 160 kDa, 7S); 2 heavy α-chains + 2 light chains **Secretory IgA (SIgA):** - **Dimer:** 2 IgA monomers joined by J-chain - **Secretory component (SC):** Poly-Ig receptor derived; protects SIgA from proteolytic digestion in mucosal secretions - Found in: Saliva, tears, colostrum, breast milk, respiratory/GI/GU secretions - **First line of mucosal defense** - prevents adherence of pathogens to epithelial cells --- ### LAQ 1. Antibody - Immunoglobulins / IgG Structure and Function *(Comprehensive - see SN 1 and SN 2 above)* **Five classes and subclasses:** | Class | Heavy chain | Subclasses | Key feature | |---|---|---|---| | IgG | γ | IgG1, IgG2, IgG3, IgG4 | Most abundant; crosses placenta | | IgA | α | IgG1, IgA2 | Mucosal immunity; SIgA | | IgM | μ | None | Pentamer; 1st response | | IgD | δ | None | B-cell surface receptor | | IgE | ε | None | Allergy; antiparasitic | --- ## ANTIGEN-ANTIBODY REACTIONS ### SN 1. Agglutination vs. Precipitation - Differences with Examples | Feature | Agglutination | Precipitation | |---|---|---| | Antigen | Particulate (cells, bacteria, inert particles coated with antigen) | Soluble antigen | | Result | Visible clumping/agglutination | Visible precipitate (line, ring, turbidity) | | Mechanism | Cross-linking of particulate antigens by antibody | Lattice formation between soluble antigen and antibody at equivalence zone | | Sensitivity | More sensitive | Less sensitive | | Examples | Widal test (S. typhi O/H agglutinins), ABO blood grouping, TPHA | Ouchterlony double diffusion, Elek's test, Immunoelectrophoresis | **Two examples of Agglutination tests:** Widal test, TPHA (Treponema pallidum hemagglutination) **Two examples of Precipitation tests:** VDRL (flocculation), Elek's immunodiffusion test --- ### SN 2. ELISA with Applications **ELISA (Enzyme-Linked Immunosorbent Assay):** **Principle:** Antibody or antigen bound to solid phase (polystyrene plate well) captures corresponding antigen/antibody from test sample; detected by enzyme-conjugated antibody; enzyme substrate produces color proportional to concentration. **Types:** 1. **Direct ELISA:** Antigen coated on plate → enzyme-labeled antibody added directly → substrate → color 2. **Indirect ELISA:** Antigen on plate → primary antibody from patient → enzyme-labeled secondary antibody → substrate → color (detects patient antibody) 3. **Sandwich ELISA:** Capture antibody on plate → antigen → detection antibody (labeled) → substrate; most sensitive; for antigen detection 4. **Competitive ELISA:** Patient antigen competes with labeled antigen for antibody binding; inversely proportional signal **Applications:** 1. **Serology:** HIV diagnosis (anti-HIV antibody), HBsAg detection, Dengue NS1 antigen, anti-HCV, anti-Toxoplasma 2. **Blood bank screening:** HIV, HBV, HCV, syphilis in donated blood 3. **Drug detection:** Therapeutic drug monitoring, drugs of abuse 4. **Hormone assays:** Pregnancy test (hCG), thyroid hormones, insulin 5. **Food testing:** Allergens, pesticide residues, food adulteration 6. **Research:** Cytokine quantification, protein assays --- ### SN 3. Agglutination Reactions - Enumerate / Widal Test / Tube Agglutination **Types of Agglutination Reactions:** 1. Direct (slide/tube) agglutination 2. Passive (indirect) agglutination - see SN 4 3. Reverse passive agglutination 4. Co-agglutination 5. Inhibition of agglutination (haemagglutination inhibition - HAI) 6. Antiglobulin (Coombs) test **Widal Test:** - **Principle:** Tube agglutination; detects agglutinating antibodies (O and H) against S. typhi in patient serum - **Procedure:** Serial doubling dilutions of patient serum (1:20 to 1:640+) mixed with standardized Salmonella antigen suspensions (TO, TH, AO, AH, BO, BH); incubate 37°C/24 hrs; read agglutination - **Interpretation:** O titre ≥1:80, H titre ≥1:160 (endemic area); fourfold rise in paired sera = diagnostic - **O agglutination:** Granular clumps (active infection); **H agglutination:** Large fluffy clumps (past infection/vaccination) **Tube Agglutination - Principle:** Patient serum diluted serially in tubes; antigen added; tube with highest dilution showing visible agglutination = titre. Advantage: quantitative; used for Brucella (SAT - standard agglutination test), Widal, Weil-Felix --- ### SN 4. Passive Agglutination Tests **Definition:** Agglutination test in which soluble antigens are artificially attached ("passively") to carrier particles, which then agglutinate in the presence of specific antibody. **Carrier particles used:** - Sheep/human RBCs → Indirect Hemagglutination (IHA) - Latex beads → Latex Agglutination Test (LAT) - Bentonite, charcoal, Staphylococcus (protein A) → co-agglutination **Examples:** 1. **TPHA/MHA-TP** (syphilis) - T. pallidum antigen on sheep RBCs 2. **RA Latex test** - IgG on latex for Rheumatoid Factor detection 3. **Latex agglutination for CSF antigens** (meningococcal/pneumococcal meningitis) 4. **RPR (Rapid Plasma Reagin)** - cardiolipin on carbon particles 5. **Wuchereria bancrofti** - IHA for filarial antibodies --- ### LAQ 1. Antigen-Antibody Reactions / Prozone Phenomenon / Agglutination **General Features of Ag-Ab Reactions:** 1. Specificity (key-lock complementarity) 2. Reversibility (non-covalent bonds: hydrogen, hydrophobic, van der Waals, ionic) 3. Proportionality (optimal ratio for visible reaction) 4. Two stages: Primary binding (rapid, invisible) → Secondary effect (visible: precipitation, agglutination) **Prozone Phenomenon:** - When antibody concentration is very high (excess) relative to antigen, each antigen molecule is saturated with antibody - no cross-linking - NO visible agglutination/precipitation - False-NEGATIVE result despite high antibody titre - Solution: Dilute the serum (test beyond prozone zone) - Seen in: Widal test, VDRL (undiluted serum in secondary syphilis), Brucella SAT **Named Reactions:** (See SN 1, 2, 3 above) --- ### LAQ 2 & 4. Precipitation Reactions - Principle / Applications **Precipitation Principle:** - Soluble antigen + antibody → insoluble lattice network → visible precipitate - Requires optimal antigen-antibody ratio (**equivalence zone**); excess antibody (prozone) or antigen (postzone) gives no precipitate **Types:** 1. **Ring (interface) test:** Antigen layered over antibody in tube; white precipitate ring at interface 2. **Ouchterlony (Double Diffusion in Agar):** Both antigen and antibody diffuse toward each other in agar; precipitin line forms where they meet at equivalence; demonstrates: identity, partial identity, non-identity 3. **Single Radial Immunodiffusion (SRID/Mancini):** Antigen diffuses into antibody-containing agar; ring diameter² ∝ antigen concentration; used to quantify Ig levels 4. **Immunoelectrophoresis:** Serum proteins separated by electrophoresis, then precipitated with antiserum; identifies M-band in myeloma 5. **Elek's test (immunodiffusion for toxin):** See Paper I answers 6. **Counterimmunoelectrophoresis (CIE):** Electrophoresis drives antigen and antibody toward each other; faster than Ouchterlony; CSF antigen detection 7. **Immunoturbidimetry/Nephelometry:** Light scattering by immune complexes; used for quantification of CRP, complement, Ig --- ## COMPLEMENT SYSTEM ### SN 1. Classical Pathway of Complement **Activation:** IgG or IgM antibody bound to antigen activates C1q **Sequence:** 1. **Recognition:** C1q binds Fc of IgM (1 molecule) or 2 IgG molecules → C1r and C1s activated → **C1 complex** 2. **C1s cleaves C4** → C4a (anaphylatoxin) + **C4b** (binds to surface) 3. **C4b + C2** → C1s cleaves C2 → C2a + C2b → **C3 convertase (C4b2a)** 4. **C3 convertase cleaves C3** → **C3a** (anaphylatoxin, chemotaxis) + **C3b** (opsonin - binds CR1 on phagocytes; also joins C4b2a) 5. **C5 convertase (C4b2a3b)** cleaves C5 → **C5a** (most potent anaphylatoxin + chemotactic) + **C5b** 6. **Terminal Complement (MAC):** C5b + C6 + C7 + C8 + C9 (poly-C9) → **Membrane Attack Complex (MAC)** → pore in bacterial membrane → lysis **Biological Effects of Complement:** 1. **Lysis** of bacteria (MAC) 2. **Opsonization** (C3b, C4b bind to CR1 on phagocytes → enhanced phagocytosis) 3. **Anaphylatoxins** (C3a, C4a, C5a) → mast cell degranulation → histamine → vasodilation, increased permeability 4. **Chemotaxis** (C5a, C3a) → attracts neutrophils and monocytes to infection site 5. **Immune complex solubilization** (C3b prevents precipitation of immune complexes) 6. **Enhancement of adaptive immunity** (C3d on antigen binds CR2 on B cells → lowers activation threshold) ### SN 2. Complement Cascade and Biological Effects *(See SN 1 above for full cascade)* **Additional - Alternative Pathway:** - Spontaneous hydrolysis of C3 → C3(H2O) → factor B binds → factor D cleaves B → C3 convertase (C3bBb, stabilized by properdin) → amplification loop - Activated by: LPS, zymosan (fungal), cobra venom factor; does NOT require antibody **Lectin Pathway:** - MBL (Mannose-Binding Lectin) binds mannose on bacteria → MASP-1, MASP-2 activated → cleave C4 and C2 (like classical) --- ## IMMUNE RESPONSE ### SN 1. Cell-Mediated Immunity (CMI) - Tests for Detection **In Vivo Tests:** 1. **Tuberculin test (Mantoux test):** 0.1 mL PPD intradermally; read induration at 48-72 hrs; tests CMI to M. tuberculosis 2. **Lepromin test (Mitsuda):** Tests CMI to M. leprae 3. **Dinitrochlorobenzene (DNCB) test:** Contact sensitization test for general CMI competence 4. **Candida/Mumps/Trichophyton skin tests:** Recall antigen tests for general CMI **In Vitro Tests:** 1. **Lymphocyte Transformation Test (LTT) / Lymphocyte Blastogenesis:** PBMCs + specific antigen → T cells proliferate → measured by ³H-thymidine incorporation or BrdU 2. **Leukocyte Migration Inhibition Test (LMIT):** T cells sensitized to antigen → release MIF (Migration Inhibitory Factor) → inhibits macrophage migration in capillary tube; positive = CMI present 3. **Cytotoxic T Lymphocyte (CTL) assay:** CD8+ T cells kill target cells; measured by ⁵¹Cr release 4. **Flow cytometry:** CD4/CD8 ratio, activation markers (CD25, CD69) 5. **ELISPOT:** Detects individual cytokine-secreting cells (IFN-γ); basis of QuantiFERON-TB Gold for latent TB 6. **Interferon-gamma release assays (IGRA)** --- ## HYPERSENSITIVITY ### SN 1. Classify Hypersensitivity / Type III - Describe **Gell and Coombs Classification:** | Type | Name | Mechanism | Antibody/Cell | Time | Examples | |---|---|---|---|---|---| | I | Immediate/Anaphylactic | IgE-mediated mast cell degranulation | IgE | Minutes | Anaphylaxis, asthma, urticaria, hay fever | | II | Cytotoxic/Antibody-mediated | IgG/IgM + complement; ADCC against cell-surface antigens | IgG, IgM | Hours | Hemolytic anemia, HDN, Goodpasture's, myasthenia gravis | | III | Immune Complex-mediated | IgG immune complexes deposited in tissues → complement activation → inflammation | IgG (soluble immune complexes) | 4-8 hrs | SLE, post-streptococcal GN, serum sickness, Farmer's lung (Arthus reaction) | | IV | Delayed-type/Cell-mediated | T cell (CD4+ Th1, CD8+ CTL) mediated | T cells (no antibody) | 48-72 hrs | TB, contact dermatitis, transplant rejection, Mantoux test | **Type III Hypersensitivity:** - **Mechanism:** Soluble antigen-antibody complexes (immune complexes) form in antigen excess → not cleared by phagocytes → deposit in vessel walls, glomeruli, synovial membranes, choroid plexus - **Complement activation** → C3a, C5a → mast cell degranulation + neutrophil chemotaxis → neutrophils release lysosomal enzymes → tissue damage - **Arthus Reaction (local Type III):** Intradermal antigen injection in immunized individual → local immune complex deposition → edema, hemorrhage, necrosis (6-8 hrs) - **Serum sickness (systemic Type III):** After injection of foreign serum (heterologous antisera, e.g., antitetanus horse serum) → fever, urticaria, arthralgia, proteinuria (7-10 days) - **Diseases:** SLE (anti-dsDNA), Post-streptococcal GN, Rheumatoid arthritis, Hypersensitivity pneumonitis (Farmer's lung, Bird fancier's lung) --- ### SN 2. Type IV Hypersensitivity **Definition:** Delayed-type hypersensitivity (DTH); cell-mediated; T-lymphocyte dependent; peaks at 48-72 hours after antigen exposure. **Mechanism:** 1. **Sensitization:** First exposure → APCs present antigen to CD4+ Th1 cells → Th1 cells sensitized (clonal expansion + memory) 2. **Elicitation (Challenge):** Re-exposure → Th1 cells recognize antigen-MHC II on APCs → release cytokines: IFN-γ (activates macrophages), TNF-β (lymphotoxin - cytotoxic), IL-2 (T cell proliferation), MIF (migration inhibitory factor) 3. **Effector:** Activated macrophages → release proteases, reactive oxygen species → tissue damage; granuloma formation in chronic DTH **Examples:** 1. Tuberculin reaction (Mantoux test) - prototype 2. Contact dermatitis (nickel, formaldehyde, poison ivy - urushiol) 3. Granulomatous hypersensitivity (TB, leprosy, sarcoidosis, schistosomiasis) 4. Transplant rejection (allograft) 5. Graft-versus-host disease --- ### SN 3. Anaphylaxis **Definition:** Acute, severe, potentially fatal systemic Type I hypersensitivity reaction mediated by IgE and mast cell degranulation. **Mechanism:** 1. Sensitization: Antigen → IgE produced → IgE binds to FcεRI on mast cells and basophils (primed state) 2. Re-exposure: Antigen cross-links 2 IgE molecules on mast cell → immediate degranulation 3. Mediators released: Histamine, prostaglandins, leukotrienes (LTC4, LTD4), PAF, tryptase 4. Effects: Vasodilation, increased vascular permeability → oedema; bronchospasm; urticaria; cardiovascular collapse **Common triggers:** Penicillin, bee venom, peanuts, shellfish, latex, blood products **Clinical features:** Urticaria, angioedema, bronchospasm, hypotension, shock, cardiac arrest **Treatment:** Adrenaline (epinephrine) 0.5 mg IM (first line); antihistamines; corticosteroids; IV fluids; oxygen --- ### LAQ 1 & 2. Hypersensitivity - Three Types of Immediate Hypersensitivity / Type I **Three Types of Immediate Hypersensitivity (Types I, II, III):** *(See table in SN 1 above and detailed Type III description)* **Type I Hypersensitivity (IgE-mediated) in Detail:** **Mechanism:** 1. **Primary exposure:** Antigen (allergen) processed by APCs → Th2 cells activated → IL-4, IL-5, IL-13 → B cells class switch to IgE 2. **Sensitization:** IgE binds to FcεRI on mast cells (skin, mucosa, lungs) and basophils - no symptoms yet 3. **Re-exposure:** Allergen cross-links adjacent IgE-FcεRI complexes on mast cell → signal transduction → Ca²⁺ influx → degranulation **Mediators:** - **Preformed (immediate, 0-30 min):** Histamine, heparin, tryptase, chemotactic factors - Histamine: H1 → vasodilation, bronchospasm, itch; H2 → gastric acid - **Newly synthesized (late, 4-6 hrs):** Prostaglandin D2, Leukotriene C4, D4, E4 (SRS-A - slow-reacting substance of anaphylaxis); PAF - LTC4/LTD4: Bronchospasm (1000x more potent than histamine), mucus secretion **Clinical Manifestations:** - **Anaphylaxis** (systemic, life-threatening) - **Allergic asthma** (bronchospasm) - **Allergic rhinitis/hay fever** (sneezing, rhinorrhea) - **Urticaria and angioedema** (skin) - **Food allergy** (peanuts, milk, eggs) - **Atopic dermatitis (eczema)** **Diagnosis:** Total IgE elevated; allergen-specific IgE (RAST/ImmunoCAP); skin prick test **Treatment:** Avoid allergen; antihistamines; beta-2 agonists (asthma); oral steroids; allergen immunotherapy (desensitization); anti-IgE (Omalizumab) --- ### LAQ 3. Hypersensitivity - Classify / Pathogenesis / Type IV *(See SN 1 and SN 2 above for complete detail)* --- ## AUTOIMMUNITY ### SN 1. Autoimmune Diseases - Four Features 1. **Presence of autoantibodies or autoreactive T cells** directed against self-antigens (e.g., anti-dsDNA in SLE, anti-acetylcholine receptor in myasthenia gravis) 2. **Association with MHC (HLA) alleles** - genetic predisposition (e.g., HLA-DR3/DR4 in Type 1 diabetes, HLA-B27 in ankylosing spondylitis) 3. **Female predominance** (most autoimmune diseases affect women more - hormonal influence) 4. **Chronicity and remission-relapse pattern** - autoimmune diseases tend to be lifelong with episodic flares ### LAQ 1. Autoimmunity - Define / Mechanisms **Definition:** Immune response (humoral or cellular) directed against self (autologous) antigens, causing tissue damage and disease. **Mechanisms of Autoimmunity:** 1. **Release of sequestered antigens:** Normally hidden antigens (lens protein, myelin, sperm) released by infection/trauma → treated as foreign → autoimmune response (sympathetic ophthalmia, orchitis) 2. **Molecular mimicry:** Microbial antigens structurally similar to self-antigens → antibodies/T cells cross-react with self tissues - Example: Streptococcal M protein → cross-reacts with cardiac myosin → rheumatic fever - Campylobacter jejuni ganglioside mimicry → Guillain-Barré syndrome 3. **Polyclonal B cell activation:** Some pathogens (EBV, LPS) activate B cells non-specifically → production of autoantibodies 4. **Epitope spreading:** Initial autoimmune response → tissue damage → release of more self-antigens → activation of additional autoreactive clones → self-perpetuating cycle 5. **Loss of peripheral tolerance:** - **Regulatory T cell (Treg) failure:** FoxP3+ Tregs suppress autoreactive cells; deficiency → autoimmunity (IPEX syndrome) - **Defective Fas/FasL apoptosis:** Autoreactive cells not deleted (ALPS - autoimmune lymphoproliferative syndrome) 6. **Bystander activation:** Inflammation near self-tissues activates APCs that present self-antigens → autoreactive T cells activated 7. **Altered self-antigens:** Drug-modified antigens (e.g., penicillin binding to red cell surface → autoimmune hemolysis), viral modification of self-proteins 8. **Superantigen stimulation:** Superantigens activate large numbers of T cells non-specifically → some autoreactive --- # VIROLOGY ## GENERAL PROPERTIES OF VIRUS ### SN 1. Egg Inoculation Method for Viral Culture **Embryonated Hen's Egg:** - 8-14 day old fertile hen's egg used - Contains 5 sites for inoculation **Routes of Inoculation and Examples:** | Route | Cavity/Membrane | Example viruses | |---|---|---| | Chorioallantoic membrane (CAM) | Surface of CAM | HSV (pocks), Vaccinia, Poxviruses | | Allantoic cavity | Allantoic fluid | Influenza, Mumps, Newcastle disease | | Amniotic cavity | Amniotic fluid | Influenza (primary isolation), Mumps | | Yolk sac | Yolk sac | Chlamydia, Rickettsia, Arboviruses, HSV | | Intravenous (vitelline vein) | Blood | Yellow fever virus | **Procedure (CAM inoculation as example):** 1. Candle the egg (7-12 days) to identify air sac and embryo 2. Mark and make a small hole over air sac; second hole over CAM 3. Suction air → CAM drops → forms artificial air sac 4. Inoculate 0.1-0.2 mL virus suspension onto CAM through 2nd hole 5. Seal holes with paraffin; incubate at 37°C for 48-72 hrs 6. Observe pock lesions on CAM **Uses of egg culture:** - Virus isolation and propagation - Vaccine production (influenza vaccine - allantoic fluid) - Virus titration (pock counting) --- ### SN 2. Methods of Detecting Viral Growth in Cell Cultures **1. Cytopathic Effect (CPE):** - Most common method; observed by inverted microscope - Cells show: rounding, swelling, shrinkage, syncytia formation (giant multinucleated cells), cell lysis - **Examples:** HSV → rapid CPE (24-48 hrs); Adenovirus → "bunch of grapes" cluster; Respiratory syncytial virus (RSV) → syncytia; CMV → "owl eye" cells **2. Haemadsorption:** - Viruses with haemagglutinin on infected cell surface adsorb guinea pig RBCs - Add RBCs to cell monolayer; wash; infected cells hold RBCs - **Used for:** Influenza, Parainfluenza, Mumps **3. Haemagglutination:** - Virus in cell culture supernatant agglutinates RBCs in wells - Used for: Influenza, Mumps **4. Interference (Heterologous interference):** - Non-cytopathic virus grows in cells → prevents CPE by cytopathic virus added later - Used for: Rubella (infects cells without CPE; detected by blocking CPE of challenge Echovirus) **5. Immunofluorescence (IF):** - Fluorescent-labeled antibodies react with viral antigens in infected cells - Direct IF: Fluorescent antibody directly; Indirect IF: Unlabeled antibody + fluorescent anti-antibody - Used for: Rabies (negri bodies), RSV, CMV, HSV **6. Metabolic Inhibition / pH change:** - Virus replication → cell death → no glucose metabolism → no acid production → medium stays red/alkaline - Used for: Enteroviruses, polioviruses **7. Transformation:** - Oncogenic viruses transform cells → loss of contact inhibition → foci of piled-up cells visible --- ### SN 3. Stages of Viral Multiplication (Replication Cycle) 1. **Adsorption (Attachment):** - Viral surface protein binds to specific host cell receptor - Example: HIV gp120 → CD4 + CCR5/CXCR4; Influenza HA → sialic acid; Rabies → acetylcholine receptor 2. **Penetration (Entry):** - **Receptor-mediated endocytosis** (most viruses) - **Membrane fusion** (enveloped viruses - HIV, Influenza) - **Direct injection** (bacteriophages - only DNA injected) - **Viropexis** (engulfment) 3. **Uncoating (Eclipse phase):** - Viral capsid removed; nucleic acid released into cytoplasm - Viral enzymes or lysosomal enzymes responsible 4. **Biosynthesis (Replication):** - **DNA viruses** (most replicate in nucleus): DNA → mRNA → viral proteins; new DNA synthesized - **RNA viruses** (replicate in cytoplasm): +ssRNA acts as mRNA; -ssRNA requires RNA-dependent RNA polymerase (RdRp); Retroviruses use reverse transcriptase (RNA → DNA → RNA) 5. **Assembly (Maturation):** - Viral components assembled into new virions - Capsid proteins surround nucleic acid 6. **Release:** - **Lysis** (non-enveloped viruses) - cell bursts → virus released - **Budding** (enveloped viruses - HIV, Influenza) - cell membrane wraps around nucleocapsid; cell may survive - **Exocytosis** (some viruses) --- ### SN 4. Embryonated Hen's Egg - Cross Section / Routes / Uses *(See SN 1 above for routes and examples)* **Cross Section of Embryonated Egg (12-day):** - Shell → Shell membrane → Air sac → Chorioallantoic membrane (CAM) → Allantoic cavity (allantoic fluid) → Amniotic cavity (amnion, amniotic fluid) → Embryo → Yolk sac **Methods of Cultivation of Viruses:** 1. Embryonated hen's egg 2. Cell (tissue) culture - most widely used today 3. Animal inoculation (laboratory animals - mice, guinea pigs, rabbits) --- ## VIRUS-HOST INTERACTIONS ### SN 1. Negri Bodies - **Definition:** Intracytoplasmic inclusion bodies found in neurons infected with Rabies virus - **Location:** Hippocampal neurons (Ammon's horn/CA1-CA4), Purkinje cells of cerebellum - **Nature:** Aggregates of rabies viral nucleocapsids (RNP - ribonucleoprotein) within cytoplasm - **Appearance:** Eosinophilic (pink), round to oval, sharply defined, 2-10 µm; contain basophilic inner granules - **Demonstration:** - **Seller's stain** (magenta/red Negri bodies against blue-grey neurons) - on brain impression smears - **H&E stain** - eosinophilic intracytoplasmic inclusions - Immunofluorescence (most sensitive and specific) - **Diagnostic significance:** Presence of Negri bodies in brain = pathognomonic of rabies - **Note:** Absent in ~20% of rabies cases; hence immunofluorescence is preferred --- ### SN 2. Inclusion Bodies **Definition:** Abnormal intracellular structures (aggregates of viral particles, viral antigens, or cellular response products) visible by light microscopy in virus-infected cells. **Two Intracytoplasmic Inclusion Bodies:** 1. **Negri bodies** - Rabies virus; neurons; eosinophilic (Seller's stain) 2. **Bollinger bodies** - Fowlpox virus; cytoplasmic; contain Borrel bodies (individual virions) 3. **Henderson-Patterson (Molluscum) bodies** - Molluscum contagiosum virus; keratinocytes 4. **Guarnieri bodies** - Vaccinia/Variola virus; cytoplasmic **Two Intranuclear Inclusion Bodies:** 1. **Cowdry type A** - HSV, VZV, CMV, Yellow fever; eosinophilic, surrounded by clear halo, marginated chromatin ("owl eye" in CMV) 2. **Cowdry type B** - Poliovirus, Rabies (older classification); multiple small, no halo 3. **Torres bodies** - Yellow fever; intranuclear eosinophilic 4. **Intranuclear inclusions of Adenovirus** - basophilic, fill nucleus ("smudge cells") --- ## VIRUSES ### SN 1. Hepatitis B - Laboratory Diagnosis **Serological Markers (Timeline):** | Marker | Significance | When appears | |---|---|---| | HBsAg | Surface antigen; first marker; active infection | 4-12 weeks | | Anti-HBc IgM | Acute/recent infection | 6-14 weeks | | HBeAg | High infectivity, active replication | With HBsAg | | HBV DNA | Most sensitive marker of replication | Early | | Anti-HBe | Seroconversion; lower infectivity | After HBeAg | | Anti-HBs | Recovery; immunity (vaccination) | >20 weeks | | Anti-HBc IgG | Past exposure (lifelong) | Persists | **Window period:** HBsAg gone but anti-HBs not yet appeared → only Anti-HBc IgM positive **Tests:** 1. **ELISA** for HBsAg, Anti-HBc, HBeAg, Anti-HBs 2. **HBV DNA by PCR** (quantitative - viral load; qualitative for occult HBV) 3. **Liver function tests** (ALT, AST elevated) 4. **Liver biopsy** for histology, fibrosis staging 5. **HBsAg by CLIA/RIA** (blood bank screening) --- ### SN 2. Rhabdoviruses - Immunoprophylaxis / Schedule / Non-neural Vaccines **Rhabdoviruses = Rabies virus (Lyssavirus genus)** **Non-Neural (Modern) Vaccines:** 1. **HDCV (Human Diploid Cell Vaccine)** - MRC-5 cells; gold standard; 1 mL IM 2. **PCECV (Purified Chick Embryo Cell Vaccine)** - Rabipur; 1 mL IM 3. **PVRV (Purified Vero Rabies Vaccine)** - Verobrab; 0.5 mL IM **Post-Exposure Prophylaxis (PEP) Schedule:** - **Wound care (most important):** Wash wound with soap and water 15 min + povidone iodine - **RIG (Rabies Immune Globulin):** Given on Day 0 only; infiltrate into wound; HRIG 20 IU/kg or ERIG 40 IU/kg - **Vaccine (Essen schedule):** Days 0, 3, 7, 14, 28 - 5 doses IM deltoid - **Zagreb (2-1-1) schedule:** Days 0(×2 sites), 7, 21 - 4 doses; WHO-approved; saves doses **Pre-Exposure Prophylaxis (PrEP):** Days 0, 7, 21/28 - 3 doses (for vets, lab workers, travelers) **Intradermal (ID) regimen (cost-saving):** 0.1 mL ID (vs 1.0 mL IM); requires trained staff; same schedule --- ### SN 3. Influenza Virus and HIV - Diagrams (Described) **Influenza Virus Structure:** - Enveloped, segmented -ssRNA virus (8 segments) - **Outer spikes:** - **Haemagglutinin (HA)** - triangular trimer; attaches to sialic acid receptors; fusion protein; vaccine target - **Neuraminidase (NA)** - mushroom-shaped tetramer; cleaves sialic acid → allows release of new virions; target of oseltamivir/zanamivir - **M2 ion channel** in envelope (target of amantadine) - **M1 protein** (matrix protein) beneath envelope - **Nucleoprotein (NP)** around RNA segments - **PB1, PB2, PA** proteins (RNA polymerase) **HIV Structure:** - Enveloped, +ssRNA retrovirus (diploid - 2 copies of RNA) - **Outer envelope:** Lipid bilayer + **gp120** (SU - surface unit; binds CD4) + **gp41** (TM - transmembrane; mediates fusion) - gp120 + gp41 = gp160 (processed by furin) - **Matrix (MA/p17):** Between envelope and core - **Core (capsid, p24):** Conical; contains 2 RNA strands + RT + IN + PR - **Enzymes:** Reverse transcriptase (p66/p51), Integrase (p32), Protease (p11) - **Genome:** gag, pol, env + accessory genes (tat, rev, vif, vpr, vpu, nef) --- ### SN 4. Type-A Influenza Virus - Antigenic Variations and Significance **Two Types of Antigenic Variation:** **1. Antigenic Drift (Minor variation):** - **Mechanism:** Accumulation of point mutations in the genes for HA and NA due to error-prone RNA polymerase (no proofreading) - **Effect:** Gradual, stepwise change in antigenic structure of HA/NA; old antibodies partially effective - **Result:** Annual seasonal epidemics (partial immunity in population); new vaccine strain needed each year - **Affects all influenza types** (A, B) **2. Antigenic Shift (Major variation):** - **Mechanism:** Reassortment of gene segments between human influenza virus and animal (avian/swine) influenza virus in a mixed-infected host (pig as "mixing vessel") - **Effect:** Sudden appearance of new HA and/or NA subtype (novel virus); no pre-existing immunity in population - **Result:** Pandemic (worldwide epidemic); high morbidity and mortality - **Only affects Type A** (has animal reservoirs); 18 HA and 11 NA subtypes known **Significance of Antigenic Variation:** - Necessitates annual influenza vaccine reformulation (WHO recommends strains twice yearly) - Basis of pandemics (1918 H1N1 "Spanish flu"; 1957 H2N2; 1968 H3N2; 2009 H1N1 "Swine flu") --- ### SN 5. Merits and Demerits of Salk's and Sabin's Vaccines | Feature | Salk's Vaccine (IPV - Inactivated Polio Vaccine) | Sabin's Vaccine (OPV - Oral Polio Vaccine) | |---|---|---| | Type | Killed/inactivated (formaldehyde) | Live attenuated | | Route | IM injection | Oral (2 drops) | | Types covered | All 3 serotypes | All 3 serotypes (trivalent/bivalent) | | Immunity induced | Humoral (IgG) - good; NO mucosal IgA | Both humoral AND mucosal (sIgA in gut) | | Herd immunity | Poor (no gut immunity; virus can still replicate in gut) | Excellent - immunized person spreads virus to contacts (passive immunization of community) | | Stability | Stable; no cold chain issues | Requires cold chain (heat labile) | | VAPP risk | None | Vaccine-Associated Paralytic Poliomyelitis (VAPP) - 1 per 2.4 million doses | | Safety | Safe in immunocompromised | Contraindicated in immunocompromised | | Cost | More expensive | Cheaper; easier to administer | | Use today | Used in polio-free countries (UK, USA) | Used in endemic areas (India now switched to bOPV + IPV) | --- ### SN 6. Classify Herpesviridae / Subfamilies / Virus / Infection | Subfamily | Characteristics | Members | One infection | |---|---|---|---| | **Alphaherpesvirinae** | Fast growth; short cycle; latency in neurons | HSV-1, HSV-2, VZV | HSV-1 → oral herpes (cold sores); VZV → chickenpox | | **Betaherpesvirinae** | Slow growth; large cells (cytomegaly); latency in glands, monocytes | CMV, HHV-6, HHV-7 | CMV → congenital CMV, retinitis in AIDS | | **Gammaherpesvirinae** | Lymphotropic; latency in lymphocytes; oncogenic | EBV (HHV-4), KSHV/HHV-8 | EBV → Infectious mononucleosis; KSHV → Kaposi's sarcoma | --- ### SN 7. HIV - Pathogenesis / Opportunistic Infections / Lab Diagnosis / HIV Testing Strategies **HIV Pathogenesis:** 1. HIV gp120 binds CD4 on Th cells + CCR5 (macrophage-tropic, early) or CXCR4 (T-tropic, late) co-receptor 2. gp41 mediates membrane fusion → viral RNA enters cell 3. Reverse transcriptase (error-prone) → proviral DNA → integrase → integrated into host chromosome (provirus) - permanent 4. Provirus latent in resting CD4 cells; activated by NF-κB → viral replication → cell death 5. CD4 count progressively declines (normal 500-1500/µL) → immune deficiency 6. CD4 < 500: Symptomatic HIV; CD4 < 200: AIDS (opportunistic infections) 7. CD8 T cells initially control viremia; exhausted over time **Two Opportunistic Infections in HIV/AIDS:** 1. **Pneumocystis jirovecii Pneumonia (PCP)** - CD4 <200; bilateral interstitial pneumonia; "ground-glass" X-ray 2. **Cryptococcal meningitis** - CD4 <100; Cryptococcus neoformans; diagnosed by India ink + serum/CSF cryptococcal antigen 3. Others: CMV retinitis, MAC infection, Toxoplasma encephalitis, esophageal candidiasis, Kaposi's sarcoma **Laboratory Diagnosis:** 1. **Screening (ELISA/CLIA):** Detects anti-HIV antibodies ± p24 antigen (4th generation tests = combo test) 2. **Confirmatory:** Western blot (bands at gp41, gp120, p24 confirm) or Line Immunoassay (LIA) 3. **CD4 count** (flow cytometry) - staging, ART initiation, monitoring 4. **HIV RNA viral load** (RT-PCR/NASBA) - treatment monitoring, diagnosis in neonates 5. **HIV p24 antigen** - detected in window period before antibodies **HIV Testing Strategies in India (NACO):** | Strategy | When | Method | |---|---|---| | Strategy I | Blood safety | Single ELISA; if +ve, blood discarded | | Strategy II | Surveillance (low prevalence) | 2 ELISAs; if discordant, 3rd test | | Strategy III | Diagnosis in symptomatic individuals | 3 sequential ELISAs with different antigens; 3 positives = HIV positive | **Window period:** 2-8 weeks after infection; antibodies not yet detectable; diagnosed by p24 antigen or viral RNA PCR (NAT) --- ### SN 8. Four Oncogenic Viruses 1. **HPV (Human Papillomavirus)** - types 16, 18 → Cervical cancer, oropharyngeal cancer; E6 (degrades p53), E7 (inactivates Rb) 2. **HBV + HCV** → Hepatocellular carcinoma (HCC) 3. **EBV (Epstein-Barr Virus)** → Burkitt's lymphoma (c-myc translocation), Nasopharyngeal carcinoma, Hodgkin's lymphoma, post-transplant lymphoma 4. **KSHV/HHV-8 (Kaposi's Sarcoma Herpesvirus)** → Kaposi's sarcoma (AIDS-defining) 5. **HTLV-1 (Human T-cell Leukemia Virus type 1)** → Adult T-cell leukemia/lymphoma (ATL) --- ### SN 9. Epstein-Barr Virus (EBV) - **Family:** Herpesviridae, Gammaherpesvirinae (HHV-4) - **Tropism:** B lymphocytes (via CD21/CR2 receptor) and epithelial cells - **Latency:** Persists in memory B cells for life **Diseases:** 1. **Infectious Mononucleosis (glandular fever, "kissing disease"):** - Fever, pharyngitis (exudative), lymphadenopathy (posterior cervical), splenomegaly, atypical lymphocytes (Downey cells - activated CD8 T cells) - **Monospot test (heterophile antibody test):** Paul-Bunnell test; EBV-infected B cells produce heterophile antibodies that agglutinate sheep/horse RBCs - **Complications:** Splenic rupture, airway obstruction, hemolytic anemia, Guillain-Barré 2. **Burkitt's Lymphoma** (endemic African type - jaw tumor in children; associated with malaria co-infection; t(8;14) c-myc translocation) 3. **Nasopharyngeal Carcinoma** (Southern China; EBV in all cases) 4. **Hodgkin's Lymphoma** (Reed-Sternberg cells contain EBV; mixed cellularity subtype) 5. **Post-transplant lymphoproliferative disorder (PTLD)** 6. **Hairy oral leukoplakia** (in HIV patients) --- ### LAQ 1. HIV - Window Period / Lab Diagnosis / Etiology / Pathogenesis *(Comprehensive - see SN 7 above)* **Window Period:** Time between HIV infection and when standard antibody tests become positive = 2-8 weeks (average 22 days with 4th generation tests, up to 3 months with 3rd generation). During window period, person is highly infectious. --- ### LAQ 2. Hepatitis - Classify / Lab Diagnosis / Pathogenesis HBV / Serological Markers / Prophylaxis **Classification of Hepatitis Viruses:** | Virus | Family | Genome | Transmission | Chronicity | Vaccine | |---|---|---|---|---|---| | HAV | Picornaviridae | +ssRNA | Feco-oral | No | Yes | | HBV | Hepadnaviridae | Partially dsDNA (circular) | Parenteral, sexual, vertical | Yes (5-10%) | Yes | | HCV | Flaviviridae | +ssRNA | Parenteral | Yes (70-80%) | No | | HDV | Deltaviridae | -ssRNA (defective; needs HBV) | Parenteral (co/super-infection) | Yes | Via HBV vaccine | | HEV | Hepeviridae | +ssRNA | Feco-oral | No (except immunocompromised) | Yes (China only) | **HBV Pathogenesis:** 1. HBV enters hepatocytes via NTCP receptor (sodium taurocholate cotransporting polypeptide) 2. Viral DNA converted to cccDNA (covalently closed circular DNA) in nucleus - template for all viral RNAs; extremely stable - basis of chronicity 3. HBV is NOT directly cytopathic; liver damage is immune-mediated (CD8+ T cell attack on HBV-infected hepatocytes) 4. Vigorous immune response → viral clearance + liver damage → acute hepatitis → resolution 5. Poor immune response (neonates, immunocompromised) → persistent infection → chronic hepatitis → cirrhosis → HCC (via integration of HBV DNA, HBx protein promoting carcinogenesis) **Serological Markers:** (See SN 1 above for Hepatitis B lab diagnosis) **HCV:** Anti-HCV ELISA (screening); HCV RNA PCR (confirmation, quantification, genotyping); HCV antigen detection **Prophylaxis:** - **HBV Vaccine:** Recombinant HBsAg (yeast-derived); 3 doses (0, 1, 6 months); >95% seroprotection - **HBIG (Hepatitis B Immune Globulin):** Passive immunization; for needle-stick, newborn of HBsAg+ mother (within 12 hrs + vaccine) - **India EPI Schedule:** HBV vaccine at birth (0), 6, 10, 14 weeks (as Pentavalent - DPT-HBV-Hib) --- ### LAQ 3. Herpes Virus - Classification / VZV / HSV *(Classification - see SN 6 above)* **VZV (Varicella-Zoster Virus / HHV-3):** **Clinical Features:** - **Varicella (chickenpox - primary infection):** - Incubation 14-21 days; fever + generalized pruritic rash - Rash: Macule → Papule → Vesicle ("dew drops on rose petal") → Pustule → Crust; crops appear simultaneously (different stages coexist) - Highly contagious; respiratory droplets + contact with lesions - **Herpes Zoster (Shingles - reactivation):** - Painful unilateral dermatomal vesicular rash; follows sensory nerve - Post-herpetic neuralgia (PHN) common complication **Lab Diagnosis of VZV:** 1. Tzanck smear (scraping from base of vesicle) → multinucleated giant cells (Cowdry A inclusions) - not specific for VZV vs HSV 2. PCR (VZV DNA) - most sensitive and specific; from vesicle fluid 3. DFA (Direct Fluorescent Antibody) with VZV-specific antibody 4. Viral culture (slow; rarely done) 5. Serology: IgM anti-VZV (acute), IgG anti-VZV (immunity) **Herpes Simplex (HSV-1, HSV-2):** **Lesions:** - **HSV-1:** Oral herpes (cold sores, herpes labialis); primary herpetic gingivostomatitis; herpes encephalitis (temporal lobe) - **HSV-2:** Genital herpes (vesicles on genitalia → ulcers); neonatal herpes; recurrent genital herpes **Lab Diagnosis of HSV:** 1. Tzanck smear - multinucleated giant cells, intranuclear inclusions 2. PCR - gold standard (vesicle fluid, CSF for encephalitis) 3. Viral culture (Vero/MRC-5 cells) - CPE in 24-48 hrs 4. DFA with HSV-1/HSV-2 specific antibodies 5. Serology: Type-specific IgG (HSV-1 vs HSV-2) by Western blot/ELISA --- ### LAQ 4. Polio Viruses - Pathogenicity / Immunoprophylaxis / Lab Diagnosis **Poliovirus:** - Family: Picornaviridae; Genus: Enterovirus - Non-enveloped, +ssRNA; 3 serotypes (1, 2, 3); Type 1 most common cause of paralysis - Stable to acid; killed by heat, chlorine, UV **Pathogenicity:** 1. Feco-oral transmission; incubation 7-14 days 2. Infects oropharyngeal and intestinal epithelium → primary replication 3. Spreads to lymph nodes (tonsils, Peyer's patches) → minor viremia 4. Major viremia → CNS (rare, <1% of infections) → anterior horn motor neurons of spinal cord and brainstem 5. Virus destroys motor neurons → asymmetric flaccid paralysis (no sensory loss) 6. **Types of infection:** - Inapparent (90-95%) - Abortive polio (minor illness - fever, headache) - Non-paralytic (aseptic meningitis) - Paralytic (spinal, bulbar, bulbospinal) 7. Post-polio syndrome: Fatigue and new muscle weakness 15-40 years after paralytic polio **Immunoprophylaxis:** (See SN 5 Salk vs Sabin above) **Lab Diagnosis:** 1. **Virus isolation:** Stool (most sensitive - shed for 3-6 weeks); throat swab; CSF (rarely) - Inoculate onto RD cells, Vero cells, HEp-2 - CPE (rounding, clumping, lysis) - Identify by neutralization with type-specific antisera 2. **PCR** (RT-PCR for poliovirus VP1 gene) - differentiates wild poliovirus from vaccine-derived (VDPV) 3. **CSF:** Pleocytosis (lymphocytes), normal glucose, elevated protein (non-specific) 4. **Serology:** Neutralization test (fourfold rise) --- ### LAQ 5. Influenza Viruses - Morphology / Antigenic Variations / Pathogenesis / Classification / Antigenic Shift **Classification:** - Family: Orthomyxoviridae - Types A, B, C (based on NP and M1 antigens - nucleoprotein and matrix) - **Type A:** Animals + humans; pandemics; 18 HA (H1-H18), 11 NA (N1-N11) subtypes - **Type B:** Humans only; seasonal epidemics; slower evolution - **Type C:** Mild illness; no HA/NA; no epidemics **Morphology:** - Enveloped, -ssRNA, 8 segments (Type A/B); pleomorphic (spherical 80-120 nm or filamentous) - HA spikes (triangular trimers) and NA spikes (mushroom tetramers) on surface in ratio ~4:1 - M1 matrix protein beneath envelope - M2 ion channel (Type A only - target of amantadine) - PB1, PB2, PA (polymerase complex), NP (nucleoprotein), NS1, NS2 **Pathogenesis:** 1. Respiratory droplet inhalation 2. HA binds sialic acid on respiratory epithelium (α2-6 linkage for human strains; α2-3 for avian) 3. Endocytosis → uncoating → RdRp synthesizes mRNA → viral proteins → assembly 4. NA cleaves sialic acid from mucus → virus reaches epithelium; also cleaves from new virions → release 5. Ciliated epithelial cells destroyed → impaired mucociliary clearance → secondary bacterial pneumonia (S. aureus, S. pneumoniae, H. influenzae) 6. **Cytokine storm** (severe influenza/H5N1/H1N1) - TNF, IL-6, IL-1 → ARDS **Antigenic Drift and Shift:** (See SN 4 above) **Antigenic Shift - Mechanism:** 1. Pig infected simultaneously with human influenza (H1N1) and avian influenza (H5N2) 2. Both viruses replicate in same pig cell → 8 gene segments of both viruses mix randomly 3. Novel reassortant virus emerges with new HA (e.g., H5) + human internal genes → pandemic strain 4. No existing population immunity → worldwide spread --- # MYCOLOGY ## GENERAL ASPECTS ### SN 1 & 2. Classify Medically Important Fungi / Morphological Classification **Classification by morphology:** | Category | Description | Examples | |---|---|---| | **Yeasts** | Unicellular; reproduce by budding; circular/oval | Candida, Cryptococcus, Malassezia | | **Moulds (Filamentous fungi)** | Multicellular; grow as hyphae/mycelium | Aspergillus, Rhizopus, Trichophyton, Sporothrix | | **Dimorphic fungi** | Exist as yeast at 37°C (tissue) and mould at 25°C (environment) | Histoplasma, Blastomyces, Coccidioides, Sporothrix, Paracoccidioides | | **Yeasts with pseudohyphae** | Elongated buds that fail to separate | Candida species | **Classification by disease caused:** | Category | Description | Organisms | |---|---|---| | **Superficial mycoses** | Skin surface, hair shaft | Malassezia furfur (pityriasis versicolor), Trichosporon | | **Cutaneous mycoses** | Skin, hair, nails (keratinized layers) | Dermatophytes (Trichophyton, Microsporum, Epidermophyton) | | **Subcutaneous mycoses** | Dermis and subcutis | Sporothrix schenckii, Madurella, Fonsecaea | | **Systemic mycoses** | Lungs and disseminate | Histoplasma, Coccidioides, Blastomyces, Paracoccidioides | | **Opportunistic mycoses** | In immunocompromised | Candida, Aspergillus, Cryptococcus, Mucor, PCP | --- ## SUPERFICIAL AND SUBCUTANEOUS MYCOSES ### SN 1. Subcutaneous Mycosis - Infection involving the dermis, subcutaneous tissue, fascia, bone following traumatic implantation of saprophytic fungi from soil/vegetation - **Examples:** 1. **Mycetoma (Madura foot)** - chronic granulomatous infection; grains in pus 2. **Sporotrichosis** - Sporothrix schenckii; "rose thorn" infection; lymphocutaneous form 3. **Chromoblastomycosis** - Fonsecaea, Phialophora; cauliflower-like verrucous lesions on limbs 4. **Rhinosporidiosis** - Rhinosporidium seeberi; polyps in nose/eye --- ### SN 2. Mycetoma - Causative Agents / Eumycetoma Lab Diagnosis **Causative Agents:** **Eumycetoma (Fungal):** - **Black grains:** Madurella mycetomatis (most common worldwide), Leptosphaeria senegalensis, Exophiala jeanselmei - **White/pale grains:** Pseudallescheria boydii (Scedosporium), Acremonium, Aspergillus **Actinomycetoma (Bacterial - Actinomycetes):** - Nocardia brasiliensis, Actinomadura madurae, Streptomyces somaliensis **Lab Diagnosis of Eumycetoma:** 1. **Pus/grain examination:** Squeeze grains → wash in saline → KOH preparation → fungal hyphae within grains 2. **Grain characteristics:** Color, texture, size help identify organism 3. **Gram stain/ZN stain:** Actinomycetoma - gram-positive filaments; fungal - broad hyphae 4. **Culture:** Sabouraud's dextrose agar (SDA) at 25-30°C; identify colony + microscopy 5. **Histopathology:** H&E - grains surrounded by Splendore-Hoeppli material; hyphae within --- ### SN 3. Dermatophytes - Classify / Lab Diagnosis **Classification (3 genera):** 1. **Trichophyton** - infects hair, skin, nails; most species - T. rubrum (most common worldwide), T. mentagrophytes, T. tonsurans 2. **Microsporum** - infects hair and skin (NOT nails) - M. canis (from dogs/cats), M. audouinii, M. gypseum 3. **Epidermophyton** - infects skin and nails (NOT hair) - E. floccosum **Classification by natural habitat:** - Anthropophilic (humans) - T. rubrum, E. floccosum - Zoophilic (animals) - M. canis, T. verrucosum - Geophilic (soil) - M. gypseum **Lab Diagnosis of Dermatophytosis:** 1. **Specimen:** Skin scrapings (from active edge), nail clippings, hair (with roots) 2. **Direct microscopy (KOH preparation):** - 10-20% KOH dissolves keratin → fungal elements visible - Skin: branching septate hyphae + arthrospores - Hair: Ectothrix (spores outside hair shaft) or Endothrix (spores inside hair shaft) 3. **Fluorescence:** Calcofluor white stain 4. **Wood's lamp:** Microsporum species fluoresce green-yellow; Trichophyton usually does NOT 5. **Culture on SDA + cycloheximide + chloramphenicol** at 25-28°C; 1-3 weeks - Macroconidia morphology identifies genus/species --- ### LAQ 1. Dermatophytes - Classify / Pathogenicity / Lab Diagnosis *(See SN 3 above)* **Pathogenicity:** - Keratinophilic and keratinolytic (produce keratinases, proteinases) - Invade stratum corneum (skin), hair shaft, nail plate - do not invade living tissue - Host reaction: Inflammation mediated by DTH (Type IV) to fungal antigens - **Tinea (ringworm) infections by site:** - Tinea capitis (scalp), T. corporis (body), T. pedis (athlete's foot), T. cruris (groin/jock itch), T. unguium/onychomycosis (nails), T. barbae (beard) --- ## SYSTEMIC AND OPPORTUNISTIC MYCOSES ### SN 1. Histoplasma capsulatum - Morphology / Growth / Pathogenesis **Morphology:** - **Dimorphic fungus** - **At 37°C (tissue form/yeast):** Small oval yeast cells (2-5 µm) with narrow-based budding; found INTRACELLULARLY in macrophages ("capsulated" = surrounded by halo but NO true capsule) - **At 25°C (environmental/mould):** White-brown cottony colonies; tuberculate macroconidia (thick-walled, spiky/thumb-nail projections) - pathognomonic; microconidia (2-5 µm) - infectious form **Growth Characters:** - SDA at 25°C: Slow-growing (2-4 weeks), white-brown cottony colony - BHI blood agar at 37°C: Cream yeast colonies - BHIB (BHI broth) with sheep blood preferred for blood cultures **Pathogenesis:** 1. Inhalation of microconidia (bat/bird droppings contaminated soil - Mississippi/Ohio River valleys) 2. Conidia reach alveoli → phagocytosed by macrophages → convert to yeast form (parasitic phase) 3. CMI develops (3-4 weeks) → granuloma formation → calcification → heals (most cases) 4. In immunocompromised (AIDS, CD4 <150): Disseminated histoplasmosis → hepatosplenomegaly, bone marrow involvement, skin lesions, oral ulcers --- ### SN 2. Opportunistic Mycoses **Definition:** Fungal infections that occur predominantly in immunocompromised hosts (HIV/AIDS, prolonged steroids, chemotherapy, transplant, diabetes, neutropenia). **Key Organisms and Infections:** 1. **Candida albicans** - oral thrush, esophageal candidiasis, vulvovaginitis, systemic candidiasis (catheter-related fungemia) 2. **Aspergillus fumigatus** - invasive pulmonary aspergillosis, aspergilloma, allergic bronchopulmonary aspergillosis (ABPA) 3. **Cryptococcus neoformans** - cryptococcal meningitis (CD4 <100 in HIV) 4. **Mucor/Rhizopus (Mucormycosis/Zygomycosis)** - rhinocerebral, pulmonary, GI, cutaneous; diabetics (DKA), COVID-19 associated mucormycosis (India 2021) 5. **Pneumocystis jirovecii** - PCP (CD4 <200; bilateral interstitial pneumonia) --- ### SN 3. Candida albicans - **Morphology:** Gram-positive oval budding yeast (3-6 µm) with pseudohyphae and true hyphae; produces chlamydospores (terminal thick-walled spores on corn meal agar) - **Germ tube test:** Candida albicans produces germ tubes (short hyphal extensions without constriction) when incubated in serum at 37°C for 2-3 hrs - **differentiates C. albicans from other Candida species** - **Reynolds-Braude phenomenon** = Germ tube test - **Culture on Sabouraud's:** White-cream, smooth, yeast-like colonies - **Diseases:** Oral thrush, esophageal candidiasis, vulvovaginitis, onychomycosis, systemic/invasive candidiasis (endocarditis, meningitis, UTI in immunocompromised) - **Virulence factors:** Adherence (Als proteins), hyphae (tissue invasion), proteinases (Saps), phenotypic switching, biofilm formation **Lab Diagnosis:** 1. KOH + Calcofluor white - pseudohyphae + yeast cells in clinical specimen 2. Gram stain - Gram-positive yeast + pseudohyphae 3. Culture: SDA; germ tube test (C. albicans); CHROMagar Candida (color-differentiation) 4. Serology: Beta-D-glucan (panfungal marker); Candida mannan antigen + anti-mannan 5. Blood culture (BACTEC) for candidemia --- ### SN 4. Aspergillosis in Humans **Causative agent:** Aspergillus fumigatus (most common), A. flavus, A. niger, A. terreus **Forms of Aspergillosis:** 1. **Allergic Bronchopulmonary Aspergillosis (ABPA):** Type I + III hypersensitivity; asthma + eosinophilia + elevated IgE + central bronchiectasis; common in asthmatics + CF patients 2. **Aspergilloma (Fungal ball):** Aspergillus colonizes pre-existing lung cavity (TB cavity, sarcoidosis) → mass of hyphae + debris; hemoptysis; X-ray: "air crescent sign" 3. **Invasive Pulmonary Aspergillosis (IPA):** Most serious; in profoundly neutropenic patients (chemotherapy, bone marrow transplant); fever, pleuritic chest pain, hemoptysis; CT: "halo sign" (hemorrhage around fungal nodule) 4. **Chronic necrotizing aspergillosis:** Slowly progressive; diabetics, COPD, alcoholics **Lab Diagnosis:** - BAL/sputum: KOH → septate hyphae with acute-angle (45°) branching (Aspergillus) - Culture: SDA - velvety green colonies with conidiophores (vesicle + phialides + conidia) - Serum Galactomannan ELISA (Aspergillus cell wall antigen; sensitive in IPA) - Beta-D-glucan (non-specific for fungi) - CT chest (halo sign/air crescent sign) + biopsy --- ### SN 5. Reynolds-Braude Phenomenon - **Same as Germ Tube Test** (Reynolds and Braude described it in 1956) - **Principle:** Candida albicans produces germ tubes (short, hypha-like extensions without constriction at point of origin) when incubated in human/fetal calf serum at 37°C for 2-3 hours - **Significance:** Rapid presumptive identification of C. albicans; C. albicans and C. dubliniensis are germ-tube positive; other Candida species (C. tropicalis, C. glabrata, C. parapsilosis) are negative - **Observation:** Under microscope: short, thin, tube-like projections from yeast cells, without constriction --- ### SN 6. Cryptococcal Meningitis - Laboratory Diagnosis **Causative agent:** Cryptococcus neoformans (serotype A/D) - CD4 <100 in HIV; Cryptococcus gattii (serotype B/C) - immunocompetent **Specimen:** CSF (LP) + Serum + Urine **Lab Diagnosis:** 1. **India ink preparation (CSF):** Negative staining; cryptococcal capsule appears as clear halo around yeast cells against dark background; "capsule" is characteristic; sensitivity ~60-80% in HIV-associated cryptococcal meningitis 2. **Cryptococcal antigen (CrAg) latex agglutination or LFA (lateral flow assay):** - Detects polysaccharide capsular antigen in CSF and serum - **Most sensitive test** (>95%); can screen serum in HIV patients - LFA (fingerstick blood test) used for screening in resource-limited settings 3. **Culture on SDA:** Mucoid, cream-colored yeast colonies; urease positive 4. **Mucicarmine stain / Alcian blue:** Stains capsule pink/blue in tissue sections 5. **CSF findings:** Elevated opening pressure, lymphocytic pleocytosis, elevated protein, low glucose --- ### SN 7. Fungi causing Opportunistic Infections in HIV / Candida Lab Diagnosis *(See SN 2, 3, 6 above and LAQ 1 below)* --- ### LAQ 1. Four Fungi Causing Opportunistic Infections / Lab Diagnosis of Candidiasis **Four Fungi:** 1. Candida albicans 2. Cryptococcus neoformans 3. Aspergillus fumigatus 4. Pneumocystis jirovecii (previously Pneumocystis carinii - formerly classified as protozoan) 5. Mucor/Rhizopus species **Lab Diagnosis of Candidiasis:** (See SN 3 above) --- # PARASITOLOGY ## FLAGELLATES ### SN 1. LD Bodies (Leishmania donovani) - **LD Bodies = Leishman-Donovan (LD) bodies = Amastigotes** - **Morphology:** Small (2-3 µm), oval, intracellular (within macrophages); contain: - Large nucleus (stains red with Leishman/Giemsa) - **Kinetoplast** (rod-shaped mitochondrial DNA; stains deeply with Leishman) - diagnostic - No free flagellum in this stage - **Location:** Within macrophages of reticuloendothelial system - spleen, liver, bone marrow, lymph nodes - **Demonstration:** 1. Splenic aspirate smear (most sensitive, >95%) - Giemsa stain: LD bodies in macrophages 2. Bone marrow aspirate (safer) 3. Liver biopsy 4. Buffy coat of blood 5. Leishman stain/Giemsa --- ### SN 2. Acute Giardiasis - Lab Diagnosis / Findings **Lab Diagnosis:** 1. **Stool examination (fresh stool):** - **Trophozoites** (in liquid/watery stool): Pear-shaped, bilaterally symmetrical, 2 nuclei ("owl-face"), 4 pairs of flagella, 2 median bodies; motility: falling leaf/tumbling - **Cysts** (formed stool): Oval; 4 nuclei; 4 flagella; 2 median bodies; 8-12 µm 2. **Concentration methods:** Formol-ether sedimentation (for cysts) 3. **Duodenal aspirate/biopsy (if stool negative):** String test (Enterotest) - capsule swallowed, string into duodenum → aspirate 4. **ELISA/RIA for Giardia antigen** in stool - most sensitive (~95%) 5. **Immunofluorescence (DIF)** with monoclonal antibody **Typical Findings:** Offensive, greasy, floating (steatorrhoeic) stool; no blood/pus (non-invasive); abdominal cramps, bloating, flatulence, malabsorption --- ### LAQ 1. Leishmania donovani - Life Cycle / Kala Azar - Pathogenicity / Lab Diagnosis **Life Cycle:** 1. **Sandfly (vector - Phlebotomus)** bites infected human → ingests macrophages with LD bodies (amastigotes) 2. In sandfly midgut: Amastigotes transform into **promastigotes** (elongated, 15-25 µm, anterior flagellum, extracellular) 3. Promastigotes multiply → migrate to proboscis 4. Sandfly bites human → inoculates **promastigotes** into skin 5. Promastigotes phagocytosed by macrophages → transform back to **amastigotes** (LD bodies) → multiply by binary fission → macrophage bursts → infects new macrophages 6. Spread via blood to spleen, liver, bone marrow, lymph nodes **Pathogenicity of Kala Azar (Visceral Leishmaniasis):** - Massive splenomegaly (most prominent sign), hepatomegaly, lymphadenopathy - Bone marrow infiltration → pancytopenia (anemia, leucopenia, thrombocytopenia) - Hypergammaglobulinemia (polyclonal IgG) - non-specific - Fever (twice daily "double quotidian" fever) - Progressive wasting, anorexia - Darkening of skin (Hindi: "Kala Azar" = black fever) - Post-Kala Azar Dermal Leishmaniasis (PKDL): Skin lesions after treatment (hypopigmented macules, nodules - reservoir of infection) **Lab Diagnosis:** 1. **Splenic aspirate** (gold standard, >95% sensitivity) - Giemsa stain: LD bodies in macrophages 2. **Bone marrow biopsy/aspirate** (safer) 3. **rK39 dipstick test:** Recombinant antigen K39 (kinesin-related protein); detects anti-Leishmania IgG; sensitivity ~90-100%; simple, rapid field test 4. **ELISA** for anti-Leishmania antibodies 5. **PCR** (blood, tissue) - most sensitive; not widely available 6. **Aldehyde test (Napier's formol gel test):** 1 drop of 40% formaldehyde → serum gels in <20 min due to hypergammaglobulinemia; not specific 7. **Montenegro test (leishmanin skin test):** Intradermal killed promastigotes → DTH reaction; NEGATIVE in active VL (anergic); positive after cure --- ## SPOROZOA ### SN 1. Malaria - Laboratory Diagnosis **Gold Standard: Thick and Thin Blood Smear (Peripheral Blood Film)** **Specimen:** Blood collected during/just before fever (paroxysm) or anytime (does not affect sensitivity much) | Smear | Advantage | Stain | |---|---|---| | Thick film | Concentrates RBCs; better sensitivity | Giemsa (or Leishman) | | Thin film | Species identification by RBC morphology; morphology best | Giemsa + fixed with methanol | **Giemsa Stain Features for Species Identification:** | Feature | P. vivax | P. falciparum | P. malariae | P. ovale | |---|---|---|---|---| | RBC size | Enlarged | Normal or small | Normal | Slightly enlarged, oval | | Schüffner's dots | Present | Absent (Maurer's clefts) | Absent | Present (James' dots) | | Trophozoite | Amoeboid | Ring forms only; accole forms; multiple rings/RBC | Band/ribbon form | Compact | | Gametocyte | Round | Banana/crescent-shaped (diagnostic) | Round | Round | **Other Tests:** 1. **RDTs (Rapid Diagnostic Tests):** Immunochromatographic strips detecting HRP-2 (P. falciparum) or pLDH (all species); point-of-care; 15 min 2. **PCR (nested PCR):** Most sensitive; species and drug resistance genotyping; research/reference labs 3. **QBC (Quantitative Buffy Coat):** Acridine orange stains malaria DNA; fluorescence microscopy; centrifuged buffy coat 4. **Serology (IFAT, ELISA):** Not for acute diagnosis; epidemiological surveys --- ### SN 2. Plasmodium falciparum - Complications / Lab Diagnosis **Complications of P. falciparum (Malignant Tertian Malaria):** 1. **Cerebral malaria:** Sequestration of parasitized RBCs in brain capillaries → coma, convulsions, herniation; mortality ~20% 2. **Severe anemia:** Hemolysis + bone marrow suppression + RBC removal by spleen 3. **Acute Renal Failure (ARF):** Tubular necrosis; "blackwater fever" (massive hemolysis + hemoglobinuria → black urine) 4. **Pulmonary edema/ARDS** 5. **Hypoglycemia:** Parasite consumes glucose + quinine stimulates insulin 6. **Disseminated Intravascular Coagulation (DIC)** 7. **Hyperparasitemia** (>5% parasitemia) 8. **Splenic rupture** 9. **Algid malaria:** Circulatory collapse, cold extremities, hypotension **Pathogenesis of complications:** - **Cytoadherence:** Parasitized RBCs express PfEMP1 (P. falciparum Erythrocyte Membrane Protein 1) on surface → bind ICAM-1, CD36, thrombospondin on endothelium → rosetting + sequestration in microvasculature → organ failure **Lab Diagnosis of P. falciparum:** (see SN 1 above; additional: only ring forms and gametocytes in peripheral blood - mature trophozoites sequester; banana-shaped gametocytes pathognomonic) --- ### LAQ 1. Malignant Tertian Malaria - Life Cycle / Complications / Lab Diagnosis **Life Cycle of P. falciparum:** **In Anopheles mosquito (sexual cycle/sporogony):** 1. Female Anopheles bites infected human → ingests gametocytes 2. Male gametocyte (microgametocyte) exflagellates → microgametes 3. Fertilization → Ookinete → penetrates midgut wall → Oocyst → Sporogony → Sporozoites 4. Sporozoites migrate to salivary glands **In Human (asexual cycle/schizogony):** 1. **Pre-erythrocytic (Exoerythrocytic) schizogony (liver):** - Mosquito inoculates sporozoites → travel to liver → infect hepatocytes - Schizogony: 1 sporozoite → 30,000 merozoites (P. falciparum - 5.5 days) - Liver schizonts rupture → merozoites released → enter RBCs - **NO HYPNOZOITE** in P. falciparum (no relapses - only recrudescences) 2. **Erythrocytic schizogony:** - Merozoite → Ring stage (trophozoite) → mature trophozoite → schizont → 16-24 merozoites → RBC ruptures → fever paroxysm (every 48 hrs - tertian) - P. falciparum: Mature trophozoites sequester in deep capillaries; only rings + gametocytes in peripheral blood **Complications and Lab Diagnosis:** (see SN 2 above) --- ### LAQ 2. Plasmodium vivax - Morphology / Life Cycle / Lab Diagnosis **Morphology of P. vivax:** - Enlarged, pale (due to Schüffner's dots), irregular-shaped RBCs - Schüffner's dots (stippling): Eosinophilic granules in infected RBC (represent knob-like projections on RBC membrane) - **Ring stage (early trophozoite):** Large ring, occupying 1/3 of RBC; one chromatin dot - **Amoeboid trophozoite:** Irregular, pseudopod-like projections; pigment (haemozoin - golden-brown) present - **Schizont:** 16-24 merozoites arranged around central pigment (rosette/daisy head) - **Gametocyte:** Large, round, fills RBC; microgametocyte (paler, diffuse chromatin); macrogametocyte (compact chromatin) **Life Cycle:** (Similar to P. falciparum but with key differences) - **Hypnozoites** (dormant forms) in liver → RELAPSES months/years later - Erythrocytic cycle: 48 hrs (Benign Tertian) - Merozoites preferentially invade young RBCs (reticulocytes) via Duffy blood group antigen (DARC) → Duffy-negative Africans are resistant **Lab Diagnosis:** (See SN 1 above - Giemsa smear; enlarged RBC + Schüffner's dots + amoeboid trophozoite) --- ## CESTODES (TAPEWORMS) ### SN 1. Hydatid Cyst - Causative Agent / Sites / Cross-Section Structure **Causative Agent:** Echinococcus granulosus (Cystic Echinococcosis) - **Definitive host:** Dog (harbors adult tapeworm) - **Intermediate host:** Sheep, cattle, humans (accidental) **Sites Affected:** 1. **Liver** (most common, 65-70%) 2. **Lung** (20-25%) 3. **Bone, brain, kidney** (rare) **Cross-Section Structure of Hydatid Cyst:** - **Pericyst (Host-derived):** Outermost layer; fibrous, avascular host tissue - **Ectocyst (Laminated membrane):** Laminated, acellular, white/opalescent - characteristic of Echinococcus - **Endocyst (Germinal/germinal layer):** Inner nucleated layer; produces protoscolices (brood capsules + scolices = "hydatid sand"), daughter cysts, and laminated membrane - **Hydatid fluid:** Clear, salty; contains scolices, brood capsules, hooks ("hydatid sand") - **Daughter cysts:** Secondary cysts within primary cyst --- ### SN 2. Echinococcus granulosus - Life Cycle 1. **Adult tapeworm** in small intestine of **dog** (definitive host); 3-6 mm, 3 proglottids (1 immature, 1 mature, 1 gravid) 2. Gravid proglottids/eggs passed in dog feces → contaminate grass, soil, water 3. **Sheep/cattle/humans** (intermediate hosts) ingest eggs 4. Egg hatches in duodenum → **oncosphere (hexacanth embryo)** with 6 hooklets → penetrates intestinal wall → portal vein → liver (first filter) 5. Some pass to lung, brain, bone via circulation 6. Oncosphere → develops into **hydatid cyst** (slowly over months-years) 7. **Dog** (definitive host) eats viscera of infected sheep → protoscolices in intestine → develop into adult tapeworms --- ### SN 3. Taenia saginata vs. Taenia solium - Four Differences | Feature | T. saginata (Beef tapeworm) | T. solium (Pork tapeworm) | |---|---|---| | Intermediate host | Cattle (beef) | Pig (pork); ALSO humans (cysticercosis) | | Scolex | No hooks, no rostellum ("unarmed") | Has hooks (22-32) on rostellum ("armed") | | Proglottids | Uterine branches: 15-30 lateral branches | Uterine branches: 7-12 lateral branches | | Danger to humans | Intestinal tapeworm only (cysticercosis does NOT occur) | Both intestinal tapeworm AND cysticercosis (neurocysticercosis - dangerous) | | Size | Longer (up to 10 m) | Shorter (2-7 m) | | Cysticercus | Not in humans | Can form in human brain, muscle, eye (cysticercosis) | **T. solium Tissue Cyst (Cysticercus cellulosae):** - Fluid-filled bladder (1 cm) with invaginated scolex; found in brain, muscles, eye, subcutaneous tissue - **Neurocysticercosis:** Most common cause of acquired epilepsy in developing world; seizures, headache, raised ICP; diagnosed by CT/MRI (calcified cysts) + serology (ELISA) **Why differentiation is necessary:** T. solium can cause cysticercosis (via autoinfection with eggs) → neurocysticercosis (life-threatening); T. saginata does NOT cause cysticercosis. Praziquantel is used for both, but treatment urgency and complications differ. --- ### LAQ 1. Cestodes - Classify / Cysticercosis - Pathogenesis **Classification of Cestodes (Tapeworms) Affecting Humans:** | Cestode | Intermediate host | Human infection | |---|---|---| | Taenia saginata | Cattle | Intestinal tapeworm | | Taenia solium | Pig; Humans | Intestinal tapeworm + Cysticercosis | | Echinococcus granulosus | Sheep/cattle/humans | Hydatid cyst | | Echinococcus multilocularis | Rodents | Alveolar echinococcosis | | Diphyllobothrium latum | Copepod → fish | B12 deficiency megaloblastic anemia | | Hymenolepis nana | Humans (no intermediate host) | Dwarf tapeworm intestinal infection | | Dipylidium caninum | Flea (dog flea) | Intestinal (children) | **Cysticercosis - Pathogenesis:** 1. **Source of infection:** Ingestion of T. solium eggs (not cysticerci) - via contaminated food/water/hands OR autoinfection (proglottid regurgitated into stomach → oncospheres released) 2. Eggs hatch in intestine → **oncospheres** penetrate intestinal wall → bloodstream 3. Disseminate to brain (most dangerous), muscles, subcutaneous tissue, eye 4. In tissue → develop into cysticercus (fluid-filled bladder with scolex) over 2-3 months 5. **Symptoms appear when cyst dies:** - Live cyst: Often asymptomatic (immune evasion) - Dying cyst: Leaks antigens → intense inflammation, edema, seizures - Dead calcified cyst: Epilepsy, headache 6. **Neurocysticercosis:** Seizures (most common symptom), raised ICP, focal neurological deficits, hydrocephalus (if cysts in ventricles) --- ### LAQ 2. Taenia solium - Morphology / Life Cycle / Pathogenesis / Lab Diagnosis **Morphology:** - **Scolex:** Globular, 1 mm; double row of hooks (22-32) on rostellum + 4 suckers ("armed tapeworm") - **Neck:** Thin, unsegmented (germinal zone) - **Strobila (body):** 800-1000 proglottids; 2-7 m length - **Gravid proglottid:** Uterus with 7-12 lateral branches (vs T. saginata 15-30); passed in feces (may be motile) - **Egg:** Round, brown, striated shell (embryophore); contains hexacanth embryo (oncosphere) with 6 hooklets; 30-40 µm **Life Cycle:** (See LAQ 1 Cestodes section above) **Pathogenesis:** 1. Intestinal taeniasis: Scolex attaches to jejunum → tapeworm; usually asymptomatic; occasional abdominal pain, weight loss, proglottids in stool 2. Cysticercosis: (See LAQ 1 above) **Lab Diagnosis:** *For Intestinal Taeniasis:* 1. **Stool examination:** Gravid proglottids (count uterine branches to differentiate T. solium from T. saginata) + eggs (round, striated) 2. Scotch tape swab (anal area - eggs like Enterobius) 3. **ELISA/Western blot** for anti-taenia antibodies (serology) *For Cysticercosis:* 1. **CT/MRI brain:** Cystic lesions (+ "dot sign" = scolex), calcifications, perilesional edema 2. **Serology:** ELISA (Cysticercus cellulosae antigen) or **Enzyme-linked immunoelectrotransfer blot (EITB/Western blot)** - most specific (>99%) and sensitive (~94%) 3. **Subcutaneous nodule biopsy:** Cysticercus on excision + histology (scolex visible) 4. **Fundoscopy:** Subretinal/vitreous cysticercus --- # NEMATODES ### SN 1. Strongyloides stercoralis Hyperinfection **Hyperinfection Syndrome:** - Occurs in immunocompromised hosts (corticosteroids, HTLV-1, AIDS, transplant, hematological malignancies) - **Mechanism:** Normal lifecycle has low-level autoinfection (rhabditiform larvae → filariform larvae in gut → penetrate colon wall → back to lungs → swallowed); in hyperinfection, this is massively amplified - **Features:** - Massive intestinal and pulmonary involvement - Larvae carry gut bacteria through intestinal wall → **Gram-negative sepsis/meningitis** (most fatal complication) - Hemorrhagic enteritis, pneumonitis, blood in stool - Larva currens (rapidly migrating urticarial skin tracks) - **Diagnosis:** Stool examination for larvae (rhabditiform); Baermann technique; serology; larvae in BAL, sputum, skin - **Treatment:** Ivermectin (drug of choice); Albendazole --- ### SN 2. Guinea Worm - Life Cycle (Dracunculus medinensis) 1. **Infected water** contains Cyclops (water flea/copepod) with L3 larvae 2. Human ingests infected Cyclops in drinking water 3. Cyclops digested in stomach → **L3 larvae released** → penetrate intestinal wall → body cavity 4. L3 larvae mature → adult worms (male 2-3 cm; female 70-120 cm) in subcutaneous tissue (lower limb, ~12-18 months) 5. Gravid female migrates to skin → blister forms (usually on leg/ankle/foot) 6. On contact with water: Blister ruptures → **female worm protrudes** → releases millions of **L1 larvae** into water 7. L1 larvae ingested by **Cyclops** → develop through L2, L3 stages within 2 weeks 8. Cycle complete **Extraction:** Traditional - slow rolling worm around stick (1-2 cm/day); do NOT break worm (releases larvae → anaphylaxis) **Control:** Filter drinking water (through fine cloth or pipe filter); treat water with Abate (temephos); health education --- ### SN 3. Occult Filariasis **Definition:** Clinical filariasis (tropical pulmonary eosinophilia - TPE) WITHOUT detectable microfilariae in peripheral blood, despite filarial infection. **Mechanism:** - Vigorous immune (IgE) response against microfilariae → microfilariae rapidly sequestered and destroyed in lungs and other tissues - **Tropical Pulmonary Eosinophilia (TPE):** - Caused by Wuchereria bancrofti or Brugia malayi - Features: Paroxysmal nocturnal cough + wheeze, breathlessness; X-ray: bilateral mottling; markedly elevated eosinophilia + high total IgE + anti-filarial IgE and IgG - Microfilariae ABSENT in blood - **Diagnosis:** High eosinophilia + high IgE + anti-filarial antibody (IgG4 ELISA) + response to DEC treatment --- ### SN 4. Wuchereria bancrofti - Morphology / Lab Diagnosis **Morphology:** - **Adult worms:** Thread-like; reside in lymphatics (inguinal lymph nodes, lymph vessels) - Male: 40 mm; Female: 80-100 mm - **Microfilariae (diagnostic stage in blood):** - Sheathed (sheath stains pink with Giemsa) - Nocturnal periodicity (maximum in peripheral blood at night 10 PM - 4 AM) - for sampling - No nuclei in tail tip (distinguishes from B. malayi which has 2 distinct nuclei in tail tip) - 244-296 µm length **Lab Diagnosis:** 1. **Blood film (thick/thin):** Collected at 10 PM-2 AM; Giemsa stain; identify microfilariae by sheath + tail nuclear pattern 2. **Concentration methods:** Knott's concentration technique (blood + formalin, centrifuge); membrane filtration (Millipore) 3. **DEC provocation test (Mazzotti test):** 50 mg DEC → microfilaraemia increases within 1 hr (can cause fever - not widely used) 4. **Serology:** Og4C3 ELISA (detects circulating filarial antigen - W. bancrofti specific); ICT card test (immunochromatographic) - detects W. bancrofti antigen; highly sensitive 5. **Ultrasonography:** "Filarial dance sign" - live adult worms in scrotal lymphatics on USG (pathognomonic) --- ### SN 5. Ectopic Ascariasis **Definition:** Migration of Ascaris lumbricoides to abnormal sites outside the gastrointestinal tract. **Sites and Clinical Syndromes:** 1. **Biliary tract:** Worm migrates through ampulla of Vater → bile duct → biliary colic, obstructive jaundice, cholangitis, cholecystitis 2. **Pancreatic duct:** Pancreatitis 3. **Appendix:** Appendicitis 4. **Liver:** Hepatic abscess (rare) 5. **Peritoneum:** Perforation of intestine → peritonitis 6. **Lungs (Löffler's syndrome):** Larval migration through lungs → eosinophilia + transient pulmonary infiltrates (not true "ectopic" but aberrant migration) **Diagnosis:** Ultrasound/ERCP shows worm in bile duct (hyperechoic elongated tubular structure) **Treatment:** Albendazole/mebendazole; ERCP extraction for biliary ascariasis --- ### LAQ 1. Intestinal Nematodes / Ascaris lumbricoides **Intestinal Nematodes (name):** 1. Ascaris lumbricoides (roundworm) 2. Enterobius vermicularis (pinworm/threadworm) 3. Trichuris trichiura (whipworm) 4. Hookworms: Ancylostoma duodenale and Necator americanus 5. Strongyloides stercoralis **Ascaris lumbricoides - Life Cycle:** 1. **Infective stage:** Embryonated egg (containing L2 larva); ingested via contaminated food/water/soil 2. Egg hatches in duodenum → **L2/L3 larvae** released → penetrate intestinal wall → portal vein → liver → heart → **lungs** (Löffler's syndrome: eosinophilia, transient pulmonary infiltrates, cough) 3. Larvae ascend airways → swallowed → reach small intestine → mature to adult worms 4. Adult worms (female 20-35 cm, male 15-30 cm) in jejunum/ileum → mate 5. Female lays **200,000 eggs/day** → passed in feces → embryonate in soil (2-4 weeks) → become infective **Pathogenicity:** - **Pulmonary:** Löffler's syndrome (larval migration) - eosinophilic pneumonia - **Intestinal:** Heavy worm burden → malnutrition, intestinal obstruction (worm bolus - most common surgical emergency in children due to parasites), volvulus - **Ectopic ascariasis** (biliary, pancreatic - see SN 5) **Lab Diagnosis:** 1. **Stool examination:** Fertilized eggs (oval, bile-stained, mammillated cortex; unfertilized eggs are longer, irregular) on direct wet mount or concentration methods 2. Adult worm passage (from mouth, anus) 3. **X-ray abdomen:** "Bunch of worms" appearance if heavy infection 4. **Ultrasound/ERCP:** Ectopic ascariasis detection **Morphology:** - **Egg (fertilized):** Oval, 60×45 µm; outer mammillated (bile-stained albuminoid) coat; inner thin shell; L1 larva inside - **Unfertilized egg:** Longer (90 µm), irregular, no larva, disorganized granular mass **Complications:** Intestinal obstruction, volvulus, intussusception, biliary/pancreatic ascariasis --- ### LAQ 2. Enterobius vermicularis - Life Cycle / Pathogenicity / Lab Diagnosis **Life Cycle:** 1. **Infective stage:** Embryonated egg (with L2 larva) 2. Eggs ingested → hatch in duodenum → larvae migrate to cecum/appendix/colon → adult worms 3. **Male** dies after copulation; **Female** (8-13 mm) migrates at night to perianal region → lays eggs (10,000 eggs/female) directly on perianal skin → dies 4. Perianal eggs embryonate rapidly (6-8 hrs) → infective 5. **Autoinfection:** Child scratches → eggs under fingernails → ingested (or retrograde infection up through anus) 6. **Retroinfection:** Larvae hatch on perianal skin → migrate back through anus → cecum **Pathogenicity:** - **Perianal pruritus** (nocturnal itching) - main symptom due to egg-laying female migrating at night - Rarely: Vulvovaginitis, ectopic appendicitis, eosinophilic peritonitis (perforation) - Sleep disturbance; secondary bacterial infection from scratching **Lab Diagnosis:** 1. **Scotch tape (cellophane tape) swab test (Graham's test):** Cellophane tape pressed on perianal region EARLY MORNING (before bathing/defecation) → placed on glass slide → microscopy → Enterobius eggs (oval, flat on one side, D-shaped; contain larva) 2. **NIH swab:** Wooden paddle smeared with adhesive → perianal swab 3. **Stool examination:** NOT useful (eggs rarely in stool); occasional worm seen --- ### LAQ 3. Nematodes - Classify **Classification by habitat in human host:** | Group | Organisms | |---|---| | **Intestinal nematodes** | Ascaris, Enterobius, Trichuris, Hookworms, Strongyloides | | **Tissue/blood nematodes (Filariae)** | Wuchereria bancrofti, Brugia malayi, Loa loa, Onchocerca volvulus, Dracunculus medinensis | | **Tissue nematodes** | Toxocara canis/cati (visceral larva migrans), Trichinella spiralis | --- ### LAQ 4 & 5. Hookworm / Ancylostoma duodenale - Life Cycle / Pathogenesis / Lab Diagnosis **Species:** - **Ancylostoma duodenale** (Old World hookworm) - 2 pairs of teeth; south Europe, Asia, Africa - **Necator americanus** (New World hookworm) - cutting plates; Americas, Africa, Southeast Asia **Ancylostoma duodenale Morphology:** - Small (A. duodenale: female 12 mm, male 8 mm), cylindrical, pinkish-white - **Scolex (buccal capsule):** 2 pairs of ventral teeth (A. duodenale) vs cutting plates (Necator) - **Copulatory bursa** in males (umbrella-like structure at posterior end) - **Egg:** Oval, thin-shelled, 60×40 µm; 4-8 cell stage when passed (segmenting); IDENTICAL for both hookworm species **Life Cycle:** 1. **Eggs passed in feces** → embryonate in warm moist soil (1-2 days) → **rhabditiform larvae** → **filariform larvae (L3) - infective stage** in 5-7 days 2. **L3 penetrate skin** (bare foot/skin contact with soil) → bloodstream → heart → **lungs** (Löffler's syndrome) 3. Cough up → swallowed → reach small intestine → mature to adult worms (3 weeks) 4. Adults attach to intestinal villi via teeth/plates → suck blood 5. **Ancylostoma duodenale** can also be ingested (oral infection - transmammary transmission in neonates possible) **Pathogenesis:** 1. **Skin (entry point):** "Ground itch" - pruritic, erythematous papulovesicular rash (usually between toes) 2. **Pulmonary:** Larval migration → Löffler's syndrome (transient cough, eosinophilia) 3. **Intestinal (main effect):** - Adult worms suck blood: A. duodenale sucks 0.2 mL/worm/day; Necator 0.02 mL - Heavy infection → **iron deficiency anemia** (most important; hypo-chromic microcytic) - Hypoproteinemia (protein-losing enteropathy) → hypoalbuminemia → edema - Malnutrition, growth retardation in children **Lab Diagnosis:** 1. **Stool microscopy (direct wet mount):** Eggs (oval, thin-shelled, 4-8 cell stage) 2. **Concentration methods:** Formol-ether sedimentation; flotation (ZnSO4/saturated salt) 3. **Stool culture (Harada-Mori technique):** Larvae allowed to hatch on filter paper → rhabditiform then filariform larvae; species identification by larval morphology 4. **Blood tests:** Eosinophilia (peripheral), microcytic hypochromic anemia; low serum iron, elevated TIBC; hypoalbuminemia 5. **Duodenal aspirate** (rarely needed) **Four Parasites Causing Anemia:** 1. **Hookworm** (A. duodenale, Necator americanus) - iron deficiency anemia (blood-sucking) 2. **Plasmodium** species - hemolytic anemia 3. **Diphyllobothrium latum** - B12 deficiency megaloblastic anemia (worm competes for B12) 4. **Leishmania donovani** - anemia from hypersplenism + bone marrow suppression --- # DIAGNOSTIC PROCEDURES ### SN 1. Stool Concentration Methods **Purpose:** Increase density of parasites from small numbers in stool to detectable levels; especially for cysts, eggs, larvae. **A. Flotation Methods (light parasites float to surface):** 1. **Zinc Sulfate Flotation (Faust's method):** - Stool + 33% ZnSO4 (specific gravity 1.18) → centrifuge → cysts/eggs float to surface (coverslip picks up surface film) - Best for: Protozoan cysts (Giardia, Entamoeba), hookworm eggs - Disadvantage: Distorts thick-shelled eggs (Ascaris fertilized), schistosome eggs, operculated eggs 2. **Saturated Salt (NaCl) Flotation:** - Uses saturated NaCl (SG 1.20); similar principle - For hookworm eggs, Enterobius eggs **B. Sedimentation Methods (heavy parasites sediment):** 1. **Formol-Ether Concentration (Ritchie's technique) - most widely used:** - Stool + 10% formalin (fixes) + diethyl ether (removes fat) - Centrifuge → cysts/eggs sediment in formalin layer - Ether (with fat debris) and formalin layers discarded; sediment examined - Best for: ALL parasites (cysts, eggs, larvae); thick-shelled eggs; operculated eggs (Taenia, Fasciola) - Advantage: Preserves morphology; kills pathogens 2. **Simple sedimentation (gravity):** Stool + water; parasites settle; rarely used **C. Special methods:** - **Baermann technique:** For Strongyloides larvae (larvae migrate up through warm water) - **Knott's concentration:** For microfilariae in blood --- ### LAQ. Parasites Detected in Blood Smear **Peripheral Blood Smear (Giemsa stained):** 1. **Plasmodium species** (P. falciparum, P. vivax, P. malariae, P. ovale) - ring trophozoites, mature stages, gametocytes 2. **Microfilariae** (Wuchereria bancrofti, Brugia malayi, Loa loa - for W. bancrofti: nocturnal periodicity; Loa loa: diurnal periodicity) 3. **Trypanosoma brucei** (African sleeping sickness) - in buffy coat/thick film; trypomastigotes 4. **Trypanosoma cruzi** (Chagas disease) - trypomastigotes in acute phase 5. **Leishmania donovani** (Kala Azar) - amastigotes in buffy coat/bone marrow (rarely peripheral blood) 6. **Babesia species** (babesiosis) - intraerythrocytic ring forms; "Maltese cross/tetrad" forms; no hemozoin --- *These answers are comprehensive, exam-ready responses for Apurva Shastri Microbiology Paper II, covering Immunology, Virology, Mycology, and Parasitology.* Create a compressed 10-12 page pdf revision guide of paper 2 answer with colour codedd section