Zoonotic bacterial infections

Zoonotic Infections - Animal Kingdom's Revenge

• Direct contact / Ingestion
  • Brucella spp.: Unpasteurized dairy → Undulant fever. 📌 Bruce Roads Units Carrying Extra Large Loads of Ammunition.
  • Leptospira: Animal urine → Weil's disease (jaundice, azotemia).
  • Pasteurella multocida: Animal bites (cats/dogs) → Cellulitis.
• Arthropod Vectors
  • Yersinia pestis: Fleas → Plague (buboes).
  • Francisella tularensis: Ticks, deer flies → Tularemia.
  • Rickettsia rickettsii: Tick → Rocky Mountain Spotted Fever.
  • Borrelia burgdorferi: Tick → Lyme disease.

⭐ Q fever (Coxiella burnetii) is a classic zoonosis without an arthropod vector. It is often acquired via inhalation of aerosols from infected animal placentas and birth fluids (cattle, sheep, goats).

Gram-Positive Zoonoses - Farm & Field Foes

• Bacillus anthracis (Anthrax)

  • Source: Spores from soil, animal hides, wool (sheep, cattle).
  • Virulence: Poly-D-glutamate capsule, Edema Toxin (↑cAMP), and Lethal Toxin (protease).
  • Forms:
    • Cutaneous: Painless papule evolves into a black eschar with significant surrounding edema.
    • Inhalational: Flu-like start, progressing to hemorrhagic mediastinitis (widened mediastinum on CXR).

• Listeria monocytogenes

  • Source: Contaminated food (deli meats, soft cheeses); survives cold temperatures.
  • Features: Tumbling motility; uses "actin rockets" for intracellular spread.
  • High-Risk: Pregnant women, neonates, elderly, and immunocompromised.

• Erysipelothrix rhusiopathiae

  • Source: Occupational exposure from handling fish, swine, or poultry.
  • Clinical: Erysipeloid-a well-demarcated, violaceous, non-suppurative cellulitis, typically on the hands.

⭐ In suspected meningitis in neonates (<3 months), the elderly (>60), or the immunocompromised, ampicillin is added to empiric therapy specifically to cover Listeria.

Gram-Negative Zoonoses - Plague & Pestilence

• Yersinia pestis (Plague)

  • Reservoir: Rodents (prairie dogs); Vector: Fleas.
  • Presents as bubonic (painful buboes), pneumonic, or septicemic plague.
  • Gram-negative coccobacillus with bipolar "safety pin" staining.
  • Tx: Streptomycin or Gentamicin.

• Francisella tularensis (Tularemia)

  • Reservoir: Rabbits; Vector: Ticks, deerflies.
  • Ulceroglandular is the most common form (skin ulcer + regional lymphadenopathy).
  • Facultative intracellular organism.
  • Tx: Aminoglycosides.

• Brucella spp. (Brucellosis)

  • Reservoir: Farm animals (cattle, goats).
  • Transmission via unpasteurized dairy.
  • Presents with undulant fever, sweats, and arthralgia.
  • Tx: Doxycycline + Rifampin.

⭐ High-Yield: Brucella is a common cause of fever of unknown origin (FUO), especially in individuals with exposure to farm animals or unpasteurized dairy products.

Spirochetal Zoonoses - Twists and Turns

• Leptospirosis (Leptospira interrogans)

  • Source: Contaminated water with animal (rodent, dog) urine.
  • Presentation: Biphasic illness. Initial flu-like symptoms & conjunctival suffusion (red eyes, no pus).
  • Severe form (Weil's Disease): Jaundice, azotemia, hemorrhagic complications, anemia.

• Borreliosis (Lyme Disease - Borrelia burgdorferi)

  • Vector: Ixodes ticks (deer tick).
  • Stages:
    • 1 (Early Localized): Erythema migrans (bull's-eye rash).
    • 2 (Early Disseminated): Bilateral Bell’s palsy, AV block.
    • 3 (Late): Migratory arthritis, encephalopathy.

⭐ A key cardiac manifestation of Lyme disease is fluctuating, high-degree AV block.

📌 Mnemonic (Lyme): Use "FACE" for key findings: Facial nerve palsy, Arthritis, Carditis, Erythema migrans.

High‑Yield Points - ⚡ Biggest Takeaways

• Brucellosis presents with undulant fever, myalgias, and arthralgias, often linked to unpasteurized dairy.
• Q fever (Coxiella burnetii) causes atypical pneumonia and hepatitis from aerosolized animal birth products.
• Tularemia (Francisella tularensis) classically presents with ulceroglandular lesions after contact with rabbits or ticks.
• Pasteurellosis (Pasteurella multocida) causes rapid-onset cellulitis following cat or dog bites.
• Leptospirosis causes fever, myalgias, and conjunctival suffusion from animal urine-contaminated water.
• Anthrax (Bacillus anthracis) is characterized by a painless black eschar in its cutaneous form.