Characterization of Trypanozoon stocks from the South Nyanza sleeping sickness focus in Western Kenya.

220 Trypanosoma (Trypanozoon) brucei sp. stocks isolated between 1969 and 1983 from the Lambwe valley sleeping sickness focus in South Nyanza, Western Kenya, were characterized by isoenzyme electrophoresis using 12 enzymes. 12 different zymodemes of T. (T.) b. rhodesiense were isolated from patients during the 13-year period and identical stocks were also found in cattle, reedbuck (Redunca redunca) and tsetse (Glossina pallidipes). Cattle may have played an important role in maintaining and increasing peridomestic transmission of trypanosomes during the 1980 outbreak of sleeping sickness in the valley, even though they themselves suffered heavy mortality. Sleeping sickness in Lambwe valley is unlikely to have been introduced from elsewhere, since T. (T.) b. rhodesiense stocks isolated from the valley were different from those from neighbouring epidemic areas. Alternatively, the recent outbreak may have been caused by the increased transmission associated with an expanding tsetse population. The possibility that genetic exchange contributed to the biochemical diversity of the trypanosomes examined is discussed.