African trypanosomiasis is caused by parasites of genus Trypanosoma and transmitted by infected tsetse flies and is endemic in 36 sub-Saharan African countries where there are tsetse flies that transmit the disease. Without treatment, the disease is considered fatal.trypanosomiasis, infectious disease in both humans and animals caused by certain members of the flagellate protozoa genus Trypanosoma (family Trypanosomatidae) and spread by certain bloodsucking insects. The life cycle of trypanosomes includes a stage spent in blood or other tissues of a vertebrate host and a stage in the gut of an invertebrate, typically a fly.