Antigen-detection enzyme immunoassays for the diagnosis of Trypanosoma vivax, T. congolense and T. brucei infections in cattle.

Species-specific monoclonal antibodies against Trypanosoma vivax, T. congolense and T. brucei were used to develop antigen-capture enzyme-linked immunosorbent assays (antigen-ELISA) for the diagnosis of bovine trypanosomiasis. Each assay was subsequently used for the detection of species-specific circulating antigens in sera of cattle experimentally infected by tsetse transmission. In T. vivax and in T. congolense-infected animals, circulating antigens were detected as early as 10-12 days post-infection while for T. brucei infections, the antigens were detected 8-14 days after challenge. The appearance of the antigens in peripheral blood generally coincided with the onset of first parasitaemia. The antigen levels increased and were persistently present in circulation even on occasions where parasitaemia was not detectable by the buffy coat technique. Following treatment with Berenil (diminazene aceturate, Hoechst, W. Germany) at a dose of 7.0 mg/kg body weight, T. vivax and T. congolense antigens were cleared from circulation within 2 weeks. The rate of removal was slower but variable in T. brucei infections. In one group of 3 animals infected with T. congolense, however, the initial decline in "antigenaemia" was followed, several weeks later, by another rise in antigenaemia, possibly heralding a relapse of the infection. Parasitaemia was not demonstrable at this stage by the buffy coat technique. The circulating antigens were partly in the form of free antigens and partly as immune complexes. Not only are these antigen-detection ELISA assays likely to be of diagnostic importance, but they may also be useful as tools for evaluation of the efficacy of treatment.