Bacterial Zoonoses

Bacterial Zoonoses Intro - Animal Kingdom's Bugs

• Bacterial infections naturally transmissible from vertebrate animals to humans (and vice-versa: anthropozoonoses).
• Causative Agents: Diverse pathogenic bacteria.
• Animal Reservoirs: Include domestic (livestock, pets) and wild animals.
• Modes of Transmission:
  • Direct contact: With infected animals, their tissues, or body fluids.
  • Indirect contact: Via vectors (e.g., ticks, fleas), fomites, contaminated environment.
  • Ingestion: Contaminated food (meat, milk) or water.
  • Inhalation: Aerosolized particles.
• Represent a major global public health burden.

⭐ Many bacterial zoonoses are occupational hazards for veterinarians, farmers, and abattoir workers.

Anthrax & Listeriosis - Positive Perils

• Anthrax (Bacillus anthracis): G+ spore-forming rod. From animals/products.

  • Cutaneous: Painless black eschar, surrounding edema. Most common.
    • 
  • Inhalational: Flu-like → hemorrhagic mediastinitis, shock. CXR: Widened mediastinum.
  • Virulence: Poly-D-glutamate capsule, tripartite toxin (PA, EF, LF).
  • Rx: Ciprofloxacin or Doxycycline.

• Listeriosis (Listeria monocytogenes): G+ rod, intracellular.

  • Transmission: Contaminated food (unpasteurized dairy, deli meats). Grows at 4°C (refrigeration).
  • Clinical:
    • Pregnant: Flu-like, risk to fetus (granulomatosis infantiseptica).
    • Neonates/Immunocompromised: Meningitis, sepsis.
  • Motility: Tumbling motility at 20-25°C; actin rockets.
  • Rx: Ampicillin (+/- gentamicin).

⭐ Anthrax: Inhalational anthrax classically presents with a widened mediastinum on chest X-ray due to hemorrhagic mediastinitis.

Brucellosis & Plague - Notorious Nasties

Brucellosis (Undulant Fever / Malta Fever)

• Causative Agent: Brucella spp. (Gram-negative coccobacilli).
• Transmission: Unpasteurized dairy, contact with infected animals.
• Clinical: Undulant fever (rising & falling), sweats, arthralgia, hepatosplenomegaly.
• Diagnosis: Blood culture (Castaneda), Rose Bengal test, SAT.
• Treatment: Doxycycline + Rifampicin (standard 6 weeks).

Plague (Black Death)

• Causative Agent: Yersinia pestis (Gram-negative rod, bipolar "safety pin" staining).
• Vector: Rat flea (Xenopsylla cheopis).
• Forms & Features:
  • Bubonic: Painful swollen lymph nodes (buboes).
  • Septicemic: DIC, shock.
  • Pneumonic: Highly infectious, hemoptysis.
• Treatment: Streptomycin or Gentamicin.

⭐ Yersinia pestis exhibits characteristic bipolar staining (Wayson or Giemsa stain), appearing like a "safety pin".

Leptospirosis & Q Fever - Query & Quagmire

Leptospirosis (Weil's Disease)

• Causative Agent: Leptospira interrogans (spirochete).
• Transmission: Contact with rodent urine-contaminated water/soil.
• Clinical: Biphasic illness.
  • 1st phase (septicemic): Fever, myalgia (esp. calves), conjunctival suffusion.
  • 2nd phase (immune/Weil's): Jaundice, renal failure, hemorrhage. 📌 JHK: Jaundice, Hemorrhage, Kidney failure.
• Diagnosis: Microscopic Agglutination Test (MAT) - Gold Standard.
• Treatment: Doxycycline, Penicillin G.

Q Fever (Query Fever)

• Causative Agent: Coxiella burnetii (obligate intracellular bacterium).
• Transmission: Inhalation of aerosols from infected livestock (esp. parturient products).
• Clinical:
  • Acute: Abrupt fever, headache, atypical pneumonia, hepatitis. No rash.
  • Chronic: Endocarditis (culture-negative), osteomyelitis.
• Diagnosis: Serology (IFA for phase I & II antibodies).

  ⭐ Coxiella burnetii endocarditis is a classic cause of culture-negative endocarditis.

• Treatment: Doxycycline (acute); Doxycycline + Hydroxychloroquine (chronic).

High‑Yield Points - ⚡ Biggest Takeaways

• Brucellosis: Undulant fever, B. melitensis commonest; occupational hazard (farmers, vets).
• Leptospirosis: Weil's disease (jaundice, renal failure, hemorrhage); from rodent urine.
• Plague: Yersinia pestis; bubonic (flea), pneumonic (droplet); bipolar staining (safety-pin).
• Anthrax: Bacillus anthracis; cutaneous eschar, inhalational (widened mediastinum); from livestock.
• Q Fever: Coxiella burnetii; atypical pneumonia, culture-negative endocarditis; from livestock aerosols.
• Tularemia: Francisella tularensis; ulceroglandular form; from ticks/rabbits.