Sleeping sickness in the Luangwa Valley of Zambia. A preliminary report of the 1982 outbreak at Kasyasya village.

Sleeping sickness (SS) in the Luangwa Valley of Zambia is widespread but generally sporadic and of low prevalence. Between March and June 1982 eleven SS cases were reported from Kasyasya village, a community of about 75 people in 12 households. Transmission most likely occurred in two periods between November 1981 and April 1982, when people were living in three groups of small farming homesteads adjacent to their fields and to woodland . Their main village was deserted for the duration of the cultivation season. The high incidence of SS at Kasyasya , particularly amongst adult females of one homestead , suggested that transmission occurred close to or within areas of habitation. Intimate contact between man, fly and the unknown reservoir was also indicated by the finding of only two, almost identical, T. rhodesiense zymodemes amongst Kasyasya cases. The zymodemes differed only by a single band in one enzyme (ALAT) of the twelve examined by starch-gel isoenzyme electrophoresis. There was no evidence for cyclical man-fly-man transmission, but mechanical transmission and single-fly transmission of a mature infection to several people may have occurred. Game animals feeding close to the homesteads were the most likely, but unproven, sources of the outbreak.