A history of Rhodesian sleeping sickness in the Lambwe Valley.

The main events in the spread of Rhodesian sleeping sickness around the eastern shores of Lake Victoria during the 1930s and 1940s are summarized and the history of the disease in the Lambwe Valley area of western Kenya is described since its appearance there in 1959. The area was very receptive to the introduction and dispersal of T. rhodesiense on account of a close association between human communities and their domestic livestock, a large tsetse (Glossina pallidipes) population, and game animals. The possible origins of the first Lambwe Valley disease focus and the epidemiological significance of the main elements of the Lambwe environment (man, tsetse, game animals) are discussed in relation to the consolidation and spread of the disease throughout the area.Between 1968 and 1971 there was a marked decline in the incidence of the disease, probably as a result of tsetse-control operations that included ground and aerial application of insecticides, bush clearance, and the efforts of the Kenya Game Department to enforce the by-laws of the Lambwe Valley Game Reserve. However, it is considered that the situation remains potentially dangerous, mainly because populations of tsetse are recovering from the effects of aerial spraying and because there is evidence that the tsetse habitats are encroaching on farming land.