Many protozoan organisms can be difficult to identify because of morphological similarities between strains or species. This is particularly true in the case of the African trypanosomes (Trypanosomaspp.). These trypanosomes are important medical and veterinary protozoan parasites that are transmitted between hosts by the tsetse fly. Correct identification is essential for the control and treatment of the diseases they cause (sleeping sickness in humans; “nagana” in cattle). The taxonomy of the AfricanTrypanosomaspp. is complex but the most economically important species areT. congolense, T. vivax, and theT. brucei“complex” (1 ). All three species infect domestic cattle, whereas two subspecies ofT. brucei (T. b. rhodesienseandT. b. gambiense) infect humans. The two human infective subspecies are morphologically identical, differing in geographical locality and symptoms caused, and, in addition, both are morphologically identical to the subspecies that infects cattle(T. b. brucei). Two levels of identification are necessary: the distinction of species and the identification of strains within a species (2 ,3 ). In the former case, the practical applications of identification include determining the presence or absence of infection and the trypanosome species responsible for the disease (diagnosis). In the latter case, identification of strains can play an important role in understanding the epidemiology of the disease.
