Some observations on the recent epidemiology of sleeping sickness in Nyanza Region, Kenya, and its relation to the general epidemiology of Gambian and Rhodesian sleeping sickness in Africa

Abstract

The history is given of sleeping sickness, of both the Gambian and Rhodesian types, in Nyanza Region, Kenya, leading up to the explosive outbreak, in Alego and the surrounding locations in 1964, of T. rhodesiense infections transmitted by G. fuscipes ( G. palpalis fuscipes). Some account is given of the characteristics of this epidemic, of the conditions that may have contributed to it and of the danger of spread to other parts of Kenya. Since this epidemic is in marked contrast to the normal association of T. gambiense with tsetse of the G. palpalis group, and of T. rhodesiense with the G. morsitans group, the reasons for these associations are considered and it is concluded that the usual combinations are the result of selective factors operating in the different conditions in which the trypanosome strains are transmitted. Laboratory and field evidence is quoted to show that there is no reason why, given suitable conditions, either type of trypanosome should not be transmitted by tsetse of either group. It is suggested that the recorded history of the movement of infected persons, the belief then current that G. morsitans did not transmit sleeping sickness, and the early incidence and localization of cases in Nyasaland and Northern Rhodesia, are consistent with the conclusion that, about 1908, a virulent strain, or strains, of Trypanosoma infective to human beings was imported from the epidemic areas of the Congo to parts of Nyasaland and Northern Rhodesia infested with tsetse of the G. morsitans group, and that this strain, or strains, capable of infecting game animals and being re-transmitted from them, gave rise to what is now known as T. rhodesiense.