An acute, usually fatal, disease of cattle and occasionally of sheep, goats, and swine, but not humans. The infection is caused by Clostridium chauvoei (C. feseri), a strictly anaerobic, spore-forming bacillus of the soil. The disease is also called symptomatic anthrax or quarter-evil. The characteristic lesions in the natural infection consist of crepitant swellings in involved muscles, which at necropsy are dark red, dark brown, or blue black. Artificial immunization is possible by use of blackleg aggressin or whole-culture bacterin. Animals surviving an attack of blackleg are permanently immune to its recurrence.