Trypanosoma brucei is a parasitic species that causes Sleeping sickness, also called Human African Trypanosomiasis, in humans and nagana in animals in Africa. It is transmitted by the infected tsetse fly. T. brucei has three subspecies:
1) T. b. brucei: It causes a wasting disease in cattle, nagana, but does not infect humans.
2) T. b. gambiense: It causes a chronic disease in humans.
3) T. b. rhodesiense: It causes an acute disease in humans.
The disease in humans is called “African sleeping sickness” due to the lethargy it induces in the infected individual.