Studies on the epidemiology of sleeping sickness in East Africa: II. Sleeping sickness in Kenya

Abstract

1. 1) A study of sleeping sickness in Kenya was undertaken at the end of 1956 and early in 1957, with extensive reference to literature and Administration and Medical records, and first-hand investigations of endemic areas in central and southern Nyanza. 2. 2) Sleeping sickness is confined to the Nyanza Province, where Trypanosoma gambiense was introduced from Uganda in 1902, and spread rapidly along the shores of Lake Victoria as far as the German border, along the southern shores of the Kavirondo Gulf, and up the Kuja and Migori rivers. Severe depopulation resulted until, between 1909 and 1912, the epidemic was abruptly checked by the people moving away from close contact with the vector, Glossina palpalis, in its habitat along the lake shores and rivers. 3. 3) The break in man-fly contact was not sufficient to eliminate the disease and it persisted as a low endemic, spreading inland to the Nyando and Yala Rivers by 1915 and 1917. 4. 4) In the late 1920's epidemics of less severity, flared up again along the lake shore, from Samia to the Uyoma Peninsula, and on the Kuja River, but were brought under a large measure of control through a well organized campaign by the Medical Department. 5. 5) Trypanosomiasis was still not eliminated, and in 1943 infections began to appear in numbers on the Kuja River and an epidemic rapidly developed, rising to nearly 300 cases a year by 1948, and in the absence of adequately planned control operations, persisting at a high level until 1954, by which time the disease had spread from an initial focus on the central Kuja to a widespread epidemic involving most of the main river and its tributaries. 6. 6) Simultaneous epidemics developed on the Nyando River, focused on Kibigori, with 287 cases in 1949 and 1950, and in Central Nyanza in the Kadimu and Alego locations, with something like over 70 cases, the exact number not having been recorded. The Nyando outbreak was admirably dealt with by the elimination of the whole G. palpalis population, an isolated one, by spraying the river and its tributaries with DDT. The Kadimu-Alego epidemic was equally effectively stopped by clearing all riparian habitat of G. palpalis throughout the infected area, but in the meanwhile a mild epidemic, with 50–100 cases a year, had moved down the Lake Victoria shores from Sakwa to Uyoma. 7. 7) Today, T. gambiense trypanosomiasis is at a low endemic level in three parts of the Nyanza Province: on the Nyando River, where 5 or 6 cases a year represent a residue of slowly developing infections, incurred before Glossina was eradicated in 1953; on the Kuja River system, still an active location for the transmission of infections, which are now being incurred mainly on headwaters and side streams; in the Sakwa-Uyoma Peninsula, where the transmission of infections was found to be taking place at four or five discrete and very circumscribed lake-shore foci. A fourth locality, Samia location adjoining the Uganda border, may have some T. gambiense, and certainly holds T. rhodesiense transmitted by G. pallidipes and is continuous with the similarly infected area in Uganda. This is a potentially dangerous situation which requires investigation, regarding both the extent and nature of the problem and the means for its control. 8. 8) The epidemiology of T. gambiense in Nyanza is discussed, and particularly the mechanism of the persistent endemic foci, which have held the disease, sometimes at a very low incidence, for periods up to 50 years, and from which the periodic epidemics have arisen. The discussion leads to the conclusion that the present period of very low endemicity offers a unique opportunity for the complete eradication of T. gambiense from this part of Kenya.