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Therapeutics in Dermatology
A reference textbook in dermatology
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Anthrax

6 April 2012, by BEGON É.

Anthrax or malcharbon (referring to the colour of the ulcers) is a bacterial infection caused by the Gram positive bacillus Bacillus anthracis, which produces a lethal poison within the host. It is an anthropozoonose that is still common in the developing countries, especially in Africa and Asia where public veterinary health programs are inadequate. It has been brought under control in the industrialised world.

Anthrax is a hydrotelluric condition. The bacteria produces spores in adverse environmental conditions and can remain dormant in the soil for long periods of time. Ingestion of the spores is the most common route by which herbivores contract anthrax. Carnivores may become infected by eating contaminated meat. In man, the skin tends to be the point of entry, either through a cut or via handling live contaminated animals or their carcasses. Some professions in contact with animals are therefore at higher risk, including farmers and abattoir workers, etc. The other modes of transmission, i.e. gastrointestinal, by eating contaminated meat or inhalation, by inhaling spores (biological warfare), are rare [2].

Anthrax is essentially a local cutaneous infection. The more serious forms, caused by passage of the germ into the bloodstream or ingestion/inhalation, are exceptional. The most common form is malignant pustule. After a silent 4 day incubation period, a single red papule emerges at the infection entry point, developing into a vesicular boil-like lesion in 24 hours. The boil becomes a depressed black eschar with a hard, raised edge. The raised edge is scattered with blisters allowing the eschar to spread until it grows to several centimetres in diameter. The surrounding skin is extremely swollen. The adjacent lymph nodes are also inflamed. The sore is not painful and does not cause a fever or constitutional symptoms. It heals spontaneously, but treatment expedites the process. Systemic infection is observed in 10 percent of cases.

Combined forms are rare. Anthrax inoculation in the eye region can cause extensive facial oedema which can spread to the respiratory tract and cause death by asphyxiation. Malignant oedema is a combination of cutaneous anthrax and intense inflammatory oedematous-bullous lesions causing toxic shock syndrome.

Inhalation anthrax, which is caused by inhalation of the spores, is very severe and results in rapidly fatal acute respiratory distress syndrome.

Diagnosis is confirmed by bacteriological analysis of samples taken from peripheral vesicles, using polychrome methylene blue (M’Fadyean reaction) [1].

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