Detection of circulating trypanosomal antigens by enzyme immunoassay

Antisera raised against Trypanosoma evansi and T. congolense were used in a double antibody sandwich enzyme immunosorbent assay (ELISA) to detect trypanosomal antigens in sera from experimentally infected rabbits and goats. Assays quantitated using reference antigen preparations and the homologous antisera showed that antigens could be detected at protein concentrations of 1.5 microgram ml-1. The antisera also cross-reacted with soluble antigens prepared from T. brucei and T. vivax at similar protein concentrations. In rabbits infected with T. evansi circulating antigens were first detected in serum four to eight days after infection and increased in levels thereafter. However, seven days after treatment with the trypanocidal drug suramin antigens were no longer detectable. In rabbits infected with T. congolense by Glossina morsitans, antigens were detected in serum 14 days after infective fly bite and had disappeared ten days after treatment with homidium chloride. Trypanosomal antigens were also detected in sera from goats infected with T. brucei and T. vivax using the antiserum prepared against T. evansi. Antigens were detected seven days after infection and maximal values observed between ten and 40 days post-infection, thereafter values declined but remained higher than pre-infection levels for up to 130 days.