The causative organism is Yersinia pestis 🦠, transmitted by the bite of infected fleas 🪳 from rodents 🐀 to humans.
It is a zoonotic pathogen and one of the most feared in history due to its role in the Black Death ⚰️.
About 📖
- Yersinia pestis: Gram-negative bacillus of the Enterobacteriaceae family.
- Causes 3 clinical forms: bubonic, septicemic, and pneumonic plague.
- First identified by Alexander Yersin in 1894.
Characteristics 🔬
- Gram-negative, rod-shaped, facultative intracellular organism.
- Facultative anaerobe (grows with/without oxygen).
- Classic “safety pin” appearance on bipolar staining (Wayson, Giemsa, immunofluorescence). 🔍
Source 🐀🪳
- Vector: The flea 🪳 feeds on infected rodents 🐁, bacteria multiply in its gut, block the midgut, and are regurgitated into new hosts.
- Reservoirs: Wild rodents and domestic rats are the key reservoirs.
- Human-to-human spread via aerosols 💨 in pneumonic plague.
- Category A potential bioterrorism agent ⚠️ (due to aerosol transmission).
Virulence 🧬
- Endotoxin (lipid A of LPS) → triggers septic shock and DIC.
- 3 major virulence plasmids:
- F1 capsular protein 🛡️: prevents phagocytosis.
- Type III secretion system 🧪: injects YOP proteins into host cells, blocking immunity.
- Plasminogen activator (Pla): helps bacterial spread and tissue invasion.
Clinical / Pathogenicity 🤒
- Bubonic plague: Fever, headache, malaise + painful swollen lymph node (“bubo” often in groin). May progress to sepsis.
- Septicemic plague: Rapid sepsis, DIC, multi-organ failure, purpura (“black death” skin changes). Mortality high if untreated.
- Pneumonic plague: Severe pneumonia, haemoptysis (bloody sputum), ARDS, shock. Highly contagious and fatal without treatment.
Investigations 🧪
- Blood cultures: Positive in septicaemia.
- Bubo aspirate / sputum: Bipolar coccobacilli on Wayson/Giemsa stain.
- Serology: Anti-F1 antibody titre >128 or seroconversion.
- PCR: Rapid confirmation.
- CXR: Bilateral pneumonia in pneumonic plague.
Management 💊
- Isolation + PPE 😷: Strict infection control for pneumonic cases.
- First-line antibiotics: Streptomycin or Gentamicin. Alternatives: Doxycycline, Ciprofloxacin, or Chloramphenicol.
- Supportive care: manage sepsis, DIC, ARDS, renal failure.
- Vaccination 💉: limited protection, less effective for pneumonic form.
- Notifiable disease 📢: immediate public health notification required.
Key Clinical Pearl ✨
Always consider plague in patients with acute febrile lymphadenitis, sepsis, or pneumonia with haemoptysis - especially if there is a history of rodent exposure, flea bites, or travel to endemic areas. Rapid isolation and treatment are life-saving.
References 📚
