A disease affecting humans and other mammals in central Africa that is caused by the parasitic protozoans Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense and is transmitted by the tsetse fly. Symptoms include fever, chills, headache, vomiting, pain in the extremities, lymph gland enlargement, anemia, depression, fatigue, coma, and eventually death if left untreated. The trypanosome is able to evade the host's immune system by frequently changing the proteins on its outer surface, by which the immune system identifies intruders.