Bubonic Plague Transmission: From Rodents to Humans

Yersinia pestis (Gram-negative coccobacillus) cycles between rodents and fleas.

Transmission Cycle

1. Enzootic cycle: Resistant rodents (e.g., ground squirrels, prairie dogs) maintain low-level circulation.
2. Epizootic amplification: Susceptible rodents (rats) die off → infected fleas (Xenopsylla cheopis) seek new hosts.
3. Flea blockage: Bacteria form biofilm in flea proventriculus → starvation → aggressive biting + regurgitation of bacteria into bite site.

Human Infection Routes

• Flea bite (primary): Bubonic plague — inguinal/axillary/cervical buboes (swollen, necrotic lymph nodes), fever, sepsis.
• Direct contact: Handling infected animal tissues/fluids → cutaneous or pharyngeal plague.
• Respiratory droplets: Pneumonic plague (secondary or primary) → person-to-person; highly fatal.
• Lab exposure: Aerosol.

Animal Infection

Carnivores (cats, dogs) get plague from eating infected rodents or flea bites. Cats develop bubonic/septicemic/pneumonic forms and can transmit to humans via droplets/scratches.

Treatment

Streptomycin, gentamicin, doxycycline, ciprofloxacin — start immediately on clinical suspicion. Mortality <10% treated; 50–60% untreated bubonic; ~100% untreated pneumonic.

Public health: rodent control, flea control, surveillance, PPE for handlers.