Trypanosoma brucei is a species of parasitic protozoan belonging to the genus Trypanosoma. It causes African trypanosomiasis, known also as sleeping sickness in humans and nagana in other 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 other animals. Only rarely can the T.b.brucei infect a human. The parasite was discovered in 1894 by Sir David Bruce, after whom the scientific name was given in 1899.