Trypanosoma brucei is a species of parasitic protozoan blonging to the genus Trypanosoma. It causes African trypanosomiasis, known also as sleeping sickness in humans and nagana in animals. T. brucei has traditionally been grouped into three subspecies: T. b. brucei, T. b. gambiense and T. b. rhodesiense. The latter two are typically parasites of humans, while the first is that of animals. Only rarely can the T.b.brucei infect a human.