Anthrax and Plague
On this page
Direct answer
Anthrax and plague are zoonotic bacterial infections caused by Bacillus anthracis and Yersinia pestis respectively, and each presents in forms that depend on the portal of entry. Cutaneous anthrax produces a painless black eschar, while plague appears as bubonic, septicaemic or pneumonic disease. Pneumonic plague is the only form transmissible from person to person through respiratory droplets, which makes it a priority for isolation.
What you must remember
- Cutaneous anthrax: A painless black eschar with surrounding oedema on exposed skin, and the commonest form of the disease worldwide.
- Inhalational anthrax: A biphasic illness with mediastinal widening on chest radiograph and haemorrhagic mediastinitis, carrying high mortality when untreated.
- Bubonic plague: A tender inguinal bubo after a flea bite, with fever, malaise and sometimes septicaemia.
- Pneumonic plague: Fulminant pneumonia with haemoptysis that is rapidly fatal, so droplet isolation and early treatment are essential.
- Treatment: Ciprofloxacin or doxycycline for anthrax, with streptomycin or gentamicin preferred for plague and doxycycline or ciprofloxacin as alternatives, per current guidance.
- Indian context: The 1994 plague outbreak in Surat, Gujarat, is the best-known Indian episode and is often cited in surveillance teaching.
A graded pathway: painless ulcer versus pneumonic illness
Consider a farmer who handles cattle and presents with a painless, black, depressed lesion on the forearm surrounded by swelling. Cutaneous anthrax must be considered until proven otherwise. A Gram stain or culture of the vesicular fluid shows large Gram-positive bacilli in chains, and colonies have a characteristic Medusa head appearance. Empirical treatment with ciprofloxacin or doxycycline starts while confirmation awaits, and systemic involvement would prompt additional agents and antitoxin in severe disease. Cutaneous lesions do not spread person to person, so contact tracing is limited. Now consider a different patient with fever, cough and bloody sputum after close contact with a family member who died of pneumonia. This is suspected pneumonic plague: the team applies droplet isolation at once, starts streptomycin or gentamicin without waiting for culture, and arranges contact tracing and chemoprophylaxis for close contacts. A Giemsa or Wayson stain of sputum or bubo aspirate shows bipolar, safety-pin staining. Public health authorities are informed at once, since plague and anthrax are both notifiable and a cluster may signal a common source or deliberate release. Laboratory staff are alerted in advance, because handling Bacillus anthracis and Yersinia pestis requires biosafety precautions.
Where the exam tries to catch you
Plague and anthrax are favourites because of their bioterrorism status, and the exam often hides the diagnosis behind a vignette. The classic pitfall is treating cutaneous anthrax as ordinary cellulitis, when the painless eschar is the key feature. Students also confuse a bubo with ordinary lymphadenitis: plague buboes are tender and rapidly enlarging after a flea bite, whereas reactive nodes from a skin infection usually are not. Pneumonic plague is the trap in infection control, because it demands droplet precautions rather than the airborne isolation used for tuberculosis. Staining details are high-yield: Bacillus anthracis is a large, non-motile, Gram-positive rod, while Yersinia pestis is a Gram-negative coccobacillus with bipolar staining.
Frequently asked questions
What is the characteristic lesion of cutaneous anthrax?
Cutaneous anthrax produces a painless, black, depressed eschar surrounded by vesicles and marked non-pitting oedema, usually on exposed skin such as the face, neck or forearm. The absence of pain is the key feature that separates it from other skin infections.
Why is pneumonic plague treated as a public health emergency?
Pneumonic plague spreads between people through respiratory droplets and progresses rapidly to fatal pneumonia, so delays in treatment are dangerous. Immediate antibiotics, droplet isolation and tracing of close contacts are needed without delay.
Which antibiotics are preferred for bubonic plague?
Streptomycin or gentamicin is preferred for plague, while doxycycline or ciprofloxacin serves as an alternative according to current guidance. Treatment should begin without waiting for culture results, because delay increases mortality.
What staining feature identifies Yersinia pestis?
Yersinia pestis shows bipolar, safety-pin staining with Giemsa or Wayson stain, because the poles of the bacillus take up the dye more strongly. This feature helps in rapid bedside laboratory identification.