Human African trypanosomiasis (HAT), or sleeping sickness, is caused by trypanosome parasites that are transmitted by tsetse flies. HAT is found only in sub-Saharan Africa. Two subspecies of Trypanosoma brucei cause disease: T. b. gambiense in West and Central Africa, and T. b. rhodesiense in East Africa.
This life-threatening disease mostly affects poor rural populations, causing significant harm. Travellers to endemic regions may also be at risk of infection.
HAT transmission requires the interaction of humans, tsetse flies and parasite reservoirs (humans, and domestic and wild animals). The animal reservoir is very important in T. b. rhodesiense and less so in T. b. gambiense, although it could explain the long-term endemicity in some foci despite control interventions.
Transmission can be interrupted by depleting the parasite reservoirs through detection and treatment of infected people and/or domestic animals and by reducing the tsetse fly population and human–tsetse contact.
In 1995, about 25 000 cases were detected, 300 000 undetected cases were estimated and 60 million people were estimated to be at risk of HAT infection. In 2001, WHO launched an initiative to reinforce control and surveillance, and HAT decreased markedly in the ensuing years. In 2019, fewer than 1000 cases were found. This reduction does not reflect a lack of control efforts as in general active and passive screening has been maintained at similar levels (around 2.5 million people screened per year).
After infection, trypanosomes multiply in the blood and lymph (first-stage, haemolymphatic) and, following a variable incubation period (from days to months), unspecific symptoms and signs such as headache, fever, weakness, joint pain, and lymphadenopathy appear.