Sleeping sickness. Illustration of a trypanosome (Trypanosoma brucei) moving past human red blood cells in the blood. This protozoan is the cause of sleeping sickness (African trypanosomiasis). It is a vector-borne parasite transmitted by blood-sucking tsetse flies (Glossina sp.). This life stage, the trypomastigote, lives in the bloodstream of the human host, reproducing asexually. It causes a recurring fever, enlarged lymph nodes, joint pain, weight loss and insomnia. Without drug treatment, the disease is usually fatal. The identical-looking trypomastigotes of T. cruzi are found in the blood of people with Chagas' disease (American trypanosomiasis).