Studies on the epidemiology of sleeping sickness in East Africa: III. The endemic area of Lakes Edward and George in Uganda

Abstract

1. 1) The endemic of Trypanosoma gambiense sleeping sickness in Busongora, in south western Uganda, started at the beginning of the century as an eastward extension of a long standing endemo-epidemic on the Semliki River in the Belgian Congo, which was brought to a fierce epidemic outbreak between 1915–1923 through Belgian administrative measures, and finally controlled by the evacuation of the whole valley in 1924–1925. The reasons for this outbreak, carried by Glossina palpalis, are described. 2. 2) In 1910 a severe but local epidemic was decimating the fishing and salt trading communities of Lakes Edward and George and the Kazinga channel, so the evacuation of the surrounding populations into the southern Ruwenzori foothills was undertaken in 1913–1914. 3. 3) The important salt trading centre of Katwe, on Lake Edward, was preserved and protected by clearings and regular inspections for sleeping sickness. 4. 4) Infection remained at a very low but persistent endemic level until 1932, when a sharp epidemic developed among the resettled population in Busongora, on the Ruwenzori slopes 12 miles north of Lake Edward. The outbreak was reduced, by clearing G. palpalis-infested rivers and by the treatment of cases, to a very low level within 3 years, but in 1942 a second epidemic occurred and spread rather more widely than the first. Again control was established by clearing and treatment so that the status of the disease here since 1949 has been that of a low endemic with two to four cases a year, and no cases since 1955. 5. 5) The endemics in Busongora were restricted to a very small area, 12 miles long by 3–4 miles wide, in which a concentration of the population and the distribution of G. palpalis on many small streams brought about such close man-fly contact as to present ideal conditions for the transmission and spread of trypanosomiasis. The 1942 epidemic started from an even more restricted endemic focus on one stream, the Bukangara, and ended up in the same small focus within which the few cases from 1953–1955 all occurred. 6. 6) Periods of very low endemicity, sometimes with no cases recorded just before the epidemic outbreaks, can be explained by the mildness of the disease and tendency to relapse to an infective state providing unsuspected sources of infection for the tsetse at these times, and by inaccuracies in the recording and detection of cases leading to underestimation of the true incidence. 7. 7) Nevertheless the present is certainly a period of very low incidence, with infections up to 1955 concentrated in one small focus on the Bukangara River. Experimental spraying on that river in 1955 effected complete though temporary disappearance of G. palpalis, and no cases have occurred in 1956 and 1957. If a careful watch on this area for a year or two more, establishes that trypanosomiasis has indeed disappeared, this incident will provide a most valuable example of the eradication of sleeping sickness during its narrowly focal endemic state with a minimum of effort.