Some principles of the epidemiology of human trypanosomiasis in Africa.

Human trypanosomiasis in Africa is treated as a disease complex in which three main elements are involved, the vertebrate host, the parasite and the insect vector, and the epidemiology is discussed in terms of the three pairs of relationships between these elements.Under host-vector relationships the significance of the type of man-fly contact is pointed out and an outline given of how it may be determined, and transmission of the disease influenced, by human activities, climatic factors and other conditions, in both Trypanosoma gambiense and T. rhodesiense sleeping-sickness.Under host-parasite relations consideration is given to the question of reservoir hosts, variations between human-infective strains in virulence, infectivity to animals and response to chemotherapy, and the relationships of these factors to one another and to the epidemiology of the disease.The complexity of factors involved in vector-parasite relations is discussed and the need for fuller information on the relative importance of these factors is stressed.