Makindo Medical Notes

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 📚

• Perry & Fetherston – Yersinia pestis: Etiologic Agent of Plague