The Mycobacterium tuberculosis complex (MTBC) includes M. tuberculosis (the cause of most human tuberculosis), M. bovis, M. bovis bacillus Calmette-Guérin (BCG, the vaccine strain), M. africanum, and M. microti. M. bovis is the main cause of tuberculosis in cattle, deer, and other mammals. The human bacillus M. tuberculosis may have evolved from M. bovis in the setting of animal domestication. Human M. bovis infection generally occurs in the setting of consumption of infected cow's milk products.