MI 9.1 - Definition of zoonoses; transmission routes (direct contact, vector-borne, foodborne) • MI 9.2 - Plague: Yersinia pestis, bubonic/septicemic/pneumonic plague, lab diagnosis • MI 9.3 - Brucellosis: Brucella species, undulant fever, diagnosis, treatment • MI 9.4 - Leptospirosis: Leptospira, Weil's disease, diagnosis, treatment • MI 9.5 - Rabies: rhabdovirus, Negri bodies, post-exposure prophylaxis, vaccination • MI 9.6 - Anthrax: Bacillus anthracis, cutaneous/pulmonary/Gl forms, bioterrorism agent, diagnosis In sabhi disease ka mujhe summary do jo mai direct learn karlu Sabke sharp point dena jo specific ho
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🦠 MI 9 - Zoonoses: Complete Sharp-Point Summary
MI 9.1 - Zoonoses: Definition & Transmission Routes
Definition: Diseases and infections whose agents are naturally transmitted between vertebrate animals and man (WHO definition).
Classification by Transmission:
| Type | Mechanism | Examples |
|---|---|---|
| Direct Zoonoses | Direct contact, fomite, mechanical vector; agent undergoes NO change | Rabies, Brucellosis, Trichinosis |
| Cyclo-Zoonoses | Need >1 vertebrate host, NO invertebrate | Taeniasis, Echinococcosis |
| Meta-Zoonoses | Transmitted by invertebrate vector (arthropod); agent multiplies in vector + extrinsic incubation period | Plague, Arboviral infections |
| Sapro-Zoonoses | Vertebrate host + non-animal reservoir (soil, organic matter) | Larva migrans, Aspergillosis |
Transmission Routes (3 main):
- Direct contact - handling infected animals/carcasses (e.g., anthrax, brucellosis)
- Vector-borne - arthropod bite (flea → plague; tick → RMSF)
- Foodborne - unpasteurized milk, undercooked meat (e.g., brucellosis, listeria)
MI 9.2 - Plague (Yersinia pestis)
The Organism:
- Gram-negative bacillus (rod)
- Reservoir: rodents (rats, squirrels, prairie dogs)
- Vector: rat flea (Xenopsylla cheopis)
- Safety Class: BSL-3; Category A bioterrorism agent
3 Clinical Forms:
| Form | Mechanism | Key Features | Mortality (untreated) |
|---|---|---|---|
| Bubonic (most common) | Flea bite → lymph node | Bubo = painful, swollen lymph node (groin/axilla); fever, chills; NO person-to-person spread | ~30-60% |
| Septicemic | Direct bacteremia or from bubonic | High fever, shock, DIC, black necrosis of extremities (Black Death); NO bubo visible | ~100% |
| Pneumonic (most dangerous) | Inhalation or hematogenous spread to lungs | Cough, hemoptysis, pneumonia; ONLY form with person-to-person spread (droplet) | ~100% if untreated |
Lab Diagnosis:
- Gram stain: Gram-negative bipolar staining ("safety pin" appearance) - also called Wayson stain
- Culture: Grows on most media; grow best at 28°C; "stalactite growth" in broth; "fried egg colonies"
- Rapid: FA (fluorescent antibody) test, PCR
- Serology: Passive hemagglutination (4-fold rise in titer)
- Specimens: bubo aspirate, blood, sputum
Treatment:
- Drug of choice: Streptomycin (gentamicin also effective)
- Alternatives: Doxycycline, chloramphenicol, TMP-SMX
- Duration: 10 days
- Prophylaxis (contacts): Doxycycline or ciprofloxacin
MI 9.3 - Brucellosis (Brucella spp.)
Species & Their Animal Hosts:
| Species | Animal Reservoir | Disease Severity |
|---|---|---|
| B. melitensis | Goats, sheep | Most severe - acute systemic |
| B. abortus | Cattle | Mild + suppurative complications |
| B. suis | Pigs | Chronic, suppurative, destructive |
| B. canis | Dogs | Mild |
Transmission (3 routes):
- Direct contact with infected animals/aborted material (occupational - veterinarians, abattoir workers, farmers)
- Ingestion - unpasteurized milk/cheese (most common civilian route)
- Inhalation - laboratory workers (aerosol)
Clinical Features - "Undulant Fever":
- Incubation: 1-4 weeks
- Fever is characteristically undulant/diurnal (rises in evening, subsides by morning)
- Also called: Malta fever, Mediterranean fever, Bang's disease
- Symptoms: malaise, chills, night sweats, fatigue, myalgias, arthralgias, weight loss
- Complications: osteoarthritis (spine - spondylitis), orchitis/epididymitis (most common complication in males), hepatosplenomegaly, endocarditis (rare but fatal)
Diagnosis:
- Gold standard: Culture (blood, bone marrow - takes 2-6 weeks; BACTEC system)
- Serology: SAT (Serum Agglutination Test) - titer ≥1:160 diagnostic; ≥4-fold rise confirmatory
- Rose Bengal test - rapid screening card test
- Coombs Brucella test - detects blocking IgG antibodies (chronic cases)
- Bone marrow culture: most sensitive (90%)
Treatment:
- DOC: Doxycycline (6 weeks) + Rifampicin (6 weeks) - combination to prevent relapse
- Alternative: Doxycycline + Streptomycin (first 2 weeks of doxy + 3 weeks streptomycin) - most effective regimen
- Complicated disease (spondylitis, endocarditis): triple therapy + longer duration
MI 9.4 - Leptospirosis (Leptospira)
The Organism:
- Spirochete (coiled, thin, highly motile with hooked ends)
- Dark-field microscopy needed (stains poorly by conventional methods; silver impregnation in tissues)
-
260 serovars; most important pathogen: Leptospira interrogans
- Key reservoir: Rats (shed organism in urine)
Transmission:
- Urine of infected animals contaminates water/soil → enters through skin abrasions or mucous membranes
- At-risk: farmers, sewage workers, soldiers, flood victims, swimmers
2 Clinical Phases:
Phase 1 - Leptospiremic Phase (days 1-7):
- High fever, severe headache, severe myalgia (especially calves), conjunctival suffusion, rash
- Leptospires detectable in blood and CSF
Phase 2 - Leptospiruric/Immune Phase (days 7-14):
- Antibodies appear; organism now in urine
- Most patients improve; ~10% develop Weil's disease
Weil's Disease (Severe Icteric Leptospirosis):
Classic triad:
- Jaundice (deep)
- Acute renal failure (most common cause of death)
- Hemorrhagic diathesis (bleeding tendency - pulmonary hemorrhage increasingly recognized)
- Also: uveitis, cardiac arrhythmias, myocarditis
Diagnosis:
- Leptospiremic phase: Blood/CSF culture, PCR, dark-field microscopy of blood
- Immune phase: Urine culture, MAT (Microscopic Agglutination Test) - gold standard serology (titer ≥1:100); ELISA IgM
- Dip-S-Ticks / Lepto dipstick - rapid field test
Treatment:
- Mild-moderate: Doxycycline 100 mg BD × 7 days (also prophylaxis: 200 mg once weekly)
- Severe (Weil's): IV Penicillin G or IV Ceftriaxone
- Supportive: dialysis for renal failure
MI 9.5 - Rabies (Rhabdovirus)
The Virus:
- Family: Rhabdoviridae, Genus: Lyssavirus
- Bullet-shaped enveloped RNA virus (negative-sense ssRNA)
- Glycoprotein G - key antigen for vaccine, induces neutralizing antibodies; responsible for cell attachment
- Neurotropic - travels via retrograde axonal transport to CNS
Transmission:
- Bite of rabid animal (dog = #1 worldwide; bats in USA)
- Contamination of wound with saliva
- NOT transmitted by contact with blood, urine, feces of rabid animal
Incubation Period:
- 10 days to 1 year (average 20-90 days)
- Shorter incubation for face/head wounds (closer to CNS)
- Longer for leg wounds
Clinical Stages:
| Stage | Duration | Features |
|---|---|---|
| Incubation | 10 days - 1 year | No symptoms |
| Prodrome | 2-10 days | Fever, headache, malaise; pain/tingling/itching at bite site (pathognomonic early sign) |
| Acute Neurologic (Furious) | 2-7 days | Hyperactivity, agitation, hydrophobia (50%), aerophobia, hypersalivation ("foaming at mouth"), hallucinations |
| Paralytic (Dumb) | Variable | Ascending paralysis (like GBS) |
| Coma → Death | Days | Respiratory paralysis = cause of death |
Negri Bodies (KEY EXAM POINT):
- Eosinophilic cytoplasmic inclusions in neurons
- Found in: hippocampus (Ammon's horn) and Purkinje cells of cerebellum (most specific sites)
- Seen in 80% of cases on histology
- Contain viral nucleocapsids
Diagnosis:
- Gold standard: Direct Fluorescent Antibody (DFA) test on brain tissue (post-mortem)
- Negri bodies: Seller's stain (ante-mortem: corneal smear or skin biopsy of nape of neck)
- PCR on saliva/CSF/skin biopsy
- Serology (useful only if vaccinated)
Post-Exposure Prophylaxis (PEP):
WHO 3-category wound classification:
| Category | Exposure | Management |
|---|---|---|
| I | Touch/feed animal, licks on intact skin | Wash; NO vaccine |
| II | Nibbling, minor scratches without bleeding | Wound wash + Vaccine |
| III | Transdermal bites/scratches, licks on mucosa, bat exposure | Wound wash + Vaccine + RIG |
Vaccine Schedule (Essen regimen): Days 0, 3, 7, 14, 28 (5 doses IM)
- Abbreviated 4-dose Zagreb regimen: Days 0 (2 doses), 7, 21
Rabies Immunoglobulin (RIG):
- HRIG (Human RIG): 20 IU/kg - inject into wound + remaining IM
- ERIG (Equine RIG): 40 IU/kg
- Give on Day 0 only; do NOT repeat
- Never give vaccine and RIG at same site
Pre-exposure prophylaxis (PrEP): 3 doses on days 0, 7, 21/28
MI 9.6 - Anthrax (Bacillus anthracis)
The Organism:
- Gram-positive, spore-forming, aerobic rod (large box-car shaped bacilli in chains)
- Spores: Main virulence; survive in soil for decades; highly resistant to heat/chemicals
- Capsule: Poly-D-glutamic acid (anti-phagocytic) - unusual as it is a polypeptide, not polysaccharide
- Category A bioterrorism agent (weaponizable spores)
Virulence Factors (Toxins):
- Protective Antigen (PA) - binds cell receptor; forms pore; delivers EF + LF (basis of vaccine)
- Edema Factor (EF) + PA = Edema Toxin (EdTx) - adenylate cyclase → massive edema
- Lethal Factor (LF) + PA = Lethal Toxin (LeTx) - metalloprotease → cell death, shock
3 Clinical Forms:
| Form | Route | Features | Mortality (untreated) |
|---|---|---|---|
| Cutaneous (most common - 95%) | Skin contact with spores | Malignant pustule → painless black eschar with surrounding edema; rarely fatal | <1% (treated), 20% untreated |
| Pulmonary/Inhalational (most deadly) | Inhaling spores (Woolsorter's disease) | Biphasic: initial flu-like illness → sudden severe respiratory distress, widened mediastinum on CXR, hemorrhagic mediastinitis | >80% |
| GI | Eating contaminated undercooked meat | Oropharyngeal or intestinal form; abdominal pain, bloody diarrhea, ascites | 25-60% |
New form: Injectional - drug users injecting heroin
Lab Diagnosis:
- Gram stain: Large Gram-positive bacilli in chains; no motile, non-hemolytic on blood agar
- Spores (central/subterminal) - detected in blood smear
- Culture: "Medusa head" colonies on blood agar (inverted fir-tree or curled hair projections)
- Confirmatory: PCR, DFA, gamma phage lysis test
- Serology: ELISA for anti-PA antibodies
Treatment:
- Cutaneous (no toxicity): Ciprofloxacin 500 mg BD × 7-10 days, OR Doxycycline, OR Amoxicillin
- Inhalational/Systemic (with toxicity): IV Ciprofloxacin + Clindamycin (protein synthesis inhibitor) ± Meropenem; treat for 60 days
- Post-exposure prophylaxis: Ciprofloxacin or Doxycycline × 60 days
- Antitoxins: Raxibacumab + Anthrax Immune Globulin for severe disease
Quick Mnemonics for Exam
Zoonoses Categories: Direct - Cyclo - Meta - Sapro = "Down Came Many Snakes"
Plague forms: "Better Stay Put" = Bubonic → Septicemic → Pneumonic (order of severity)
Brucella species severity: melitensis > suis > abortus/canis - "Most Severe = Melitensis"
Brucellosis Rx: "Doxy + Rif = DR (Doctor's choice)"
Rabies Negri bodies sites: "Hippo Purkinje" = Hippocampus + Purkinje cells
Anthrax toxin: PA = "Postman" delivering EF and LF to the cell
Anthrax forms frequency: Cutaneous > GI > Pulmonary (but Pulmonary = deadliest)
Sources: Medical Microbiology 9e (Murray), Sherris Medical Microbiology 8e, Goldman-Cecil Medicine, Harrison's Principles 22e, Park's Preventive Medicine, Rosen's Emergency Medicine
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