[Bacillus anthracis: causative agent of anthrax].

Anthrax, an acute infectious disease of historical importance, is once again regaining interest with its use as a biological weapon. It is caused by B. anthracis, a Gram positive spore forming rod usually surrounded by a capsule and producing toxin. It occurs most frequently as an epizootic or enzootic disease of herbivores that acquire spores form direct contact with contaminated soil. Spores can survive for many years in soil. Animal vaccination programs have reduced drastically the disease in developed countries. In humans, the disease is acquired following contact with anthrax infected animals or their products. 3 types of anthrax infection can occur: cutaneous, inhalational and gastro intestinal. Cutaneous anthrax is the most common observed form. When germination occurs, replicating bacteria release toxin leading to hemorrhage, edema, necrosis and death. Full virulence of B. anthracis requires the presence of both antiphagocytic capsule and 3 toxin components (protective antigen, lethal factor and edema factor). Most naturally occurring anthrax strains are sensitive to penicillin but resistant to third generation cephalosporins. Post exposure prophylaxis is indicated to prevent inhalational anthrax.