Gastrointestinal anthrax begins with ingestion of contaminated meat. The spores are transported to mesenteric or regional lymph nodes, where they undergo replication and dissemination. The incubation period is 2-5 days after ingestion. The host subsequently becomes bacteremic with a high mortality rate. A subset of this disease is oropharyngeal anthrax.
Virulence depends on the bacterial capsule and the anthrax toxin complex.
Experiments in the 20th century by Sterne showed that an unencapsulated strain attenuates anthrax. The anthrax toxins are composed of 3 entities, the protective antigen, lethal factor and edema factor. The protective antigen is a 83 kd protien that binds to the target cell receptors. Once bound, a 20 kd fragment is proteolysed, thus exposing an additional binding site. The toxin complex is then transported to the cytosol where edema toxin acts by converting adenosine triphosphate to cyclic adenosine monophosphate.