Question
Cutaneous anthrax
Answer
Cutaneous anthrax (historically termed “malignant pustule”) is the most common clinical form of anthrax (caused by Bacillus anthracis), acquired through inoculation of spores into broken/abraded skin, typically from contact with infected animals, hides, wool, or animal products — usually the mildest and most treatable form of anthrax when appropriately managed.
Clinical evolution: a small, characteristically painless (or minimally painful), pruritic papule at the site of inoculation, typically on an exposed area of skin; over 1–2 days, this evolves through a vesicular stage and then ulcerates, developing a characteristic black, depressed, necrotic eschar surrounded by marked, often extensive, non-pitting oedema. Regional lymphadenopathy and mild systemic symptoms may accompany the lesion.
Pathogenesis: local germination of spores at the inoculation site, with bacterial multiplication and toxin production (protective antigen, oedema factor, lethal factor) driving the marked local oedema and tissue necrosis.
Complications: if untreated, can progress to bacteraemia and systemic anthrax with high mortality, though the cutaneous form has a good prognosis (<1% mortality) with prompt antibiotic treatment.
Laboratory diagnosis: Gram stain and culture of vesicular fluid/eschar material (large, Gram-positive, spore-forming, box-car shaped bacilli, non-haemolytic on blood agar, characteristic non-motile “Medusa head” colonies); PCR where available.
Treatment: ciprofloxacin or doxycycline; surgical incision/manipulation of the lesion is avoided, as it risks precipitating systemic dissemination.