Human African trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. It is caused by infection with protozoan parasites belonging to the genus Trypanosoma.
These parasites are transmitted to humans by tsetse fly (Glossina genus) bites which have acquired their infection from human beings or from animals harbouring the pathogenic parasites.
Tsetse flies are found just in sub-Saharan Africa though only some species transmit the disease.
Depending on the parasite species involved, the sleeping sickness takes two forms: Trypanosoma brucei gambiense, accounts for over 98% of reported cases and causes a chronic infection; and Trypanosoma brucei rhodesiense, that, nowadays, represents under 2% of reported cases and causes an acute infection.