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.
Of the various known species of Trypanosoma, only two—T. cruzi and T. brucei—cause disease in humans. Each species is responsible for a different disease. Trypanosoma cruzi causes American trypanosomiasis, also called Chagas disease, which occurs primarily in the Central and South American tropics and is spread by the bite of reduviid bugs (family Reduviidae), particularly Triatoma infestans, also known as “kissing bugs.” The parasite multiplies in the bloodstream and may enter the heart, liver, and spleen, where it causes extensive damage.
Trypanosoma brucei is responsible for African trypanosomiasis, or sleeping sickness, which occurs in equatorial Africa in two forms, both transmitted by the tsetse fly (Glossina). East African, or Rhodesian, sleeping sickness is an acute form of the disease caused by the subspecies T. brucei rhodesiense. West African, or Gambian, trypanosomiasis is a slower-developing chronic form of the disease caused by T. brucei gambiense. Both organisms can eventually invade the brain, causing mental deterioration, coma, and death.
Other Trypanosoma species cause economically important diseases in livestock: nagana, dourine, surra, and mal de caderas.