A species with three subspecies: T. brucei brucei, T. brucei gambiense, and T. brucei rhodesiense. The subspecies T. brucei brucei causes a wasting disease in cattle called nagana but does not produce disease in humans. The subspecies T. brucei gambiense causes African sleeping sickness in western and central Africa. The subspecies T. brucei rhodesiense, transmitted by the tsetse fly, causes African sleeping sickness in eastern and southern Africa.
A parasite responsible for causing the disease known as nagana in horses and various domestic animals in tropical regions of Africa.