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Anthrax, Cutaneous

Pictures of anthrax and disease information have been excerpted from VisualDx clinical decision support system as a public health service. Additional information, including symptoms, diagnostic pearls, differential diagnosis, best tests, and management pearls, is available in VisualDx.

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Synopsis

Cutaneous anthrax is a bacterial infection caused by Bacillus anthracis, an encapsulated, gram-positive, spore-forming bacillus. Although inhalational and gastrointestinal forms of anthrax exist, approximately 95% of all anthrax cases are cutaneous. Injectional anthrax is another form of infection, usually characterized by severe soft tissue infection. Outbreaks have occurred, mainly in Europe, among heroin users.

Bacillus anthracis has been classified by the CDC as a Category A bioterrorism agent due to its high lethality, hardiness, and ease of weaponization. The spores, which are resistant to heat, UV light, microwave radiation, and many otherwise useful disinfectants, can remain dormant in soil for years. The identification of patients with cutaneous anthrax may be the first evidence of an anthrax attack.

Cutaneous anthrax lesions evolve from pruritic papules to clusters of vesicles to ulcers within 1-2 days following exposure of abraded skin or wounds to the spores. The ulcers then develop into depressed black eschars over the next 2-5 days. The most common areas affected are the arms, face, and neck. The incubation period is 1-12 days.

With antibiotic treatment, the mortality rate for cutaneous anthrax is approximately 1%. However, without treatment, it may progress to a systemic form of anthrax with a mortality rate of approximately 20%. In these cases, the spores introduced into the body are eaten by macrophages and taken to regional lymph nodes, where they germinate into bacteria. Released into the lymph system, they enter the blood stream, causing septicemia-releasing toxins that result in a fatal toxemia.

Bacillus anthracis is present in both domestic and wild animals throughout the world (mainly in agricultural regions of South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East) and can be transmitted by their meat, wool, or hides. Therefore, veterinarians and those in the meat-, wool-, or hide-processing industries (including construction of traditional drums) are the most at risk for contracting naturally occurring cutaneous anthrax. Cutaneous anthrax can also be acquired during the sacrifice of infected animals such as sheep, goats, cattle, water buffalo, antelopes, elephants, giraffes, and zebras. Anthrax is rarely found in animals in the United States. Bacillus anthracis is not routinely found in US soil, although it can be found in soil where previously infected animals have died. Major epizootics in the past have occurred in North Dakota, South Dakota, Minnesota, and Texas.

Look For

An initial pruritic macule or papule that enlarges into a plaque by the second day. Vesicles 1-3 mm in size can then appear, sometimes coalescing into bullae. They can discharge clear to serosanguineous fluid, with numerous organisms seen on gram stain. Then, a painless black eschar develops at the center, with extensive local edema. The eschar loosens and falls off in 2-3 weeks, leaving no permanent scar. Lymphangitis and painful lymphadenopathy are common.

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