APPLICATION OF A MONOCLONAL ANTIBODY-BASED ANTIGEN-DETECTION ENZYME-LINKED-IMMUNOSORBENT-ASSAY (ANTIGEN ELISA) FOR FIELD DIAGNOSIS OF BOVINE TRYPANOSOMIASIS AT NGURUMAN, KENYA

A monoclonal antibody-based, enzyme immunoassay (antigen ELISA) for the detection of species-specific invariant antigens of Trypanosoma congolense, T. vivax or T. brucei in the serum of infected animals was evaluated as a means of diagnosis using bovine field sera from a trypanosomiasis endemic area, Nguruman, Kenya. Circulating trypanosome antigens were detected in 126 (96.2%) of 131 serum samples from animals with parasitologically confirmed diagnosis: 74.8% were positive for antigens of two or three trypanosome species, while 21.4% tested positive for one trypanosome species. When 70 sera from animals (at Nguruman), which had tested negative for trypanosomes by the buffy coat technique, were tested, 35 (50.0%) of them were shown to be antigen-ELlSA positive: 24 (34.3%) showing infection with a single species and 11(15.7%) with mixed infections. The predominant trypanosome species diagnosed in the two herds by antigen ELISA was T. vivax, which was detected in 133 (82.6%) of the 161 sera that tested positive for antigens, followed by T. congolense in 122 (75.8%) sera, with 109 (67.7%) showing evidence of mixed infections with two or three trypanosome species. In single infections, T. vivax exceeded T. congolense by a ratio of 2:1, with T. brucei accounting for less than 1.0%. Evidence for the specificity of the test was provided by analysis of field sera from 100 cattle, from a trypanosomiasis-free area, infected with other haemoparasites (anaplasmosis, babesiosis and theileriosis), which all tested negative in the assay.