Evaluation of three antigen detection tests (monoclonal trapping ELISA) for African trypanosomes, with an isolate of Trypanosoma vivax from French Guyana.

Preliminary studies in French Guyana with sheep experimentally infected with a local isolate of Trypanosoma vivax tended to show poor sensitivity and/or specificity of the monoclonal antibodies used in kits for the antigen-detection (Ag) ELISA for T. vivax, T. brucei, and T. congolense. To reevaluate these kits, 4 calves were infected at ILRAD, Nairobi, Kenya, with the same isolate. Blood samples were taken daily for 51 days, and examined directly on blood smears and buffy coat, and using Ag-ELISA for the three species. For the 4 calves, on 158 tests performed over the first 51 days of infection, the percentages of positive results were 66% on buffy coat; on Ag-ELISA 3.8% for T. vivax, 4.4% for T. brucei, and 3.1% for T. congolense. Blood smears showed only T. vivax. These results confirm those previously obtained in French Guyana: the test for T. vivax (at least in the initial stage) shows a very low sensitivity, far below that of parasitological techniques, and the specificity of the T. brucei and T. congolense tests is low. Certain surprising results obtained in Africa might also be due to a poor sensitivity and specificity of the monoclonals used. As ELISA is the technic of choice for epidemiological surveys, and antigen detection a logical way to confirm whether an animal is actively infected by trypanosomes, the Ag-ELISA remains a necessary tool for epidemiological surveys of trypanosomes; new monoclonals are required to develop more specific and sensitive tests.