A history of sleeping sickness in Kenya.

Gambian sleeping sickness entered what is now Kenya from Uganda in about 1901 and quickly spread along the Kenyan shores and islands of Lake Victoria, reaching Tanzania in 1902. By 1910 the disease had spread 25 miles inland along the Kuja and Migori rivers and their tributaries. Sleeping sickness waxed and waned in these areas despite attempts to control tsetse fly populations by various methods. It was not until 1950, when the use of insecticides (DDT) applied by backpack sprayer proved successful against Glossina fuscipes at Kibigori, that eradication of G. fuscipes and Gambian sleeping sickness seemed possible. Subsequently the Kuja-Migori endemic area was cleared of flies and disease, as well as the South and Central Nyanza lake shores and islands. By 1965 Gambian sleeping sickness had virtually disappeared from Kenya. A more virulent form of the disease, Rhodesian sleeping sickness, may have also spread to Kenya from Uganda, although its appearance in diverse areas of the Gambian disease suggest that local ecological factors may have played a role in enhanced virulence of trypanosomes stocks. The Rhodesian form of sleeping sickness appeared in the Lambwe Valley, South Nyanza, in about 1959, and despite attempts to eradicate this disease it still persists as the only remaining endemic area in Kenya at this time. The usual transmission of Rhodesian sleeping sickness by G. pallidipes in Kenya was altered when an outbreak occurred at Alego, in Central Nyanza, in 1964. It was discovered that G. fuscipes was the vector and that domestic cattle were an important reservoir of infection. Glossina fuscipes was also the vector of Rhodesian sleeping sickness in an outbreak in Samia in 1976 and another along the lakeshore in South Nyanza in 1981. Sleeping sickness has been restricted primarily to the Western and Nyanza Provinces of Kenya (Fig. 1).