African trypanosomiasis or sleeping sickness is a parasitic disease of humans and other animals. It is caused by protozoa of the species Trypanosoma brucei. There are two types that infect humans, Trypanosoma brucei gambiense (T.b.g) and Trypanosoma brucei rhodesiense (T.b.r.). T.b.g causes over 98% of reported cases. Both are usually transmitted by the bite of an infected tsetse fly and are most common in rural areas.