Bacillus anthracis coordinates the expression of its virulence factors in response to a specific environmental signal. Anthrax toxin proteins and the antiphagocytic capsule are produced in response to growth in increased atmospheric CO 2 . This CO 2 signal is thought to be of physiological significance for a pathogen which invades mammalian host tissues. Immunity Considerable variation in genetic susceptibility to anthrax exists among animal species. This is illustrated in the table below.
Second attacks are extremely rare.
Permanent immunity to anthrax seems to require antibodies to both the toxin and the capsular polypeptide, but the relative importance of the two kinds of antibodies appears to vary widely in different animals. A nonencapsulated toxigenic strain has been used effectively in livestock. The Sterne Strain of Bacillus anthracis produces sublethal amounts of the toxin that induces formation of protective antibody. The anthrax vaccine for humans, which is used in the U.S., is a preparation of the protective antigen recovered from from the culture filtrate of an avirulent, nonencapsulated strain of Bacillus anthracis that produces PA during active growth. Currently, the anthrax vaccine is produced under contract to the Department of Defense, and only small quantities are made available as needed to civilians who are exposed to anthrax hazards in their work environment, such as veterinarians, lab workers and others.