Characterization of potentially man-infective Trypanosoma brucei from an endemic area of sleeping sickness in Kenya.

Human trypanosomiasis caused by Trypanosoma brucei rhodesiense has affected the human population in Lambwe Valley, western Kenya, for more than 20 years. A characteristic feature of the disease has been the repeated recrudescense at restricted residual foci. Studies carried out on the incidence of trypanosome infection rates in the vector Glossina pallidipes during the last two years have shown high incidence of pathogenic African trypanosomes in the area. An overall trypanosome infection rate of 18.6% was recorded. T. vivax accounted for 15% of all infected flies whereas T. congolense was detected in 2.7% of flies examined. T. brucei infections were observed in 0.9% of the flies. Twenty-six T. brucei isolates were tested for their sensitivity to human plasma using Blood Incubation Infectivity Test (BIIT), and 14 (54%) gave positive BIIT reactions. Isoenzyme characterisation of all BIIT positive isolates was carried out in order to detect any variations within these potentially man-infective T. brucei. Of the seven zymodemes observed, two were more frequently represented. Zymodeme (Z1) was represented by five stocks. This zymodeme was completely identical electrophoretically to T.b. rhodesiense isolated from patients in the same locality. Zymodeme (Z4) was represented by four stocks. This zymodeme does not have the ALAT I in combination with PGM II and ICD II patterns which are characteristic of typical West African T.b. gambiense. The high frequency of PGM III and ICD III strongly suggested the occurrence of hybridization of zymodemes in the area.