Human African trypanosomiasis, or sleeping sickness, is caused by infection with protozoan parasites belonging to the genus Trypanosoma. The disease is vector-borne; parasites enter the body through the bites of tsetse flies (Glossina spp). Without prompt diagnosis and treatment, the disease is usually fatal: the parasites multiply in the body, cross the blood–brain barrier and invade the central nervous system. Sleeping sickness is found in remote sub-Saharan areas where health systems are often weak.

T. b. gambiense is endemic in 24 countries of west and central Africa and causes more than 94% of reported cases of sleeping sickness in 2024. T. b. rhodesiense is endemic in 13 countries of eastern and southern Africa, representing about 6% of reported cases in 2024. Between 1999 and 2024, the reported number of new cases of the chronic form of human African trypanosomiasis (T. b. gambiense) fell by 98%, from 27 862 to 546. During the same period, the number of newly reported cases of the acute form of human African trypanosomiasis (T. b. rhodesiense) fell by 94% from 619 to 37.