Sensitivity of antigen ELISA test for detecting Trypanosoma evansi antigen in horses in the subtropical area of Argentina.

The sensitivity of an antigen detection enzyme immunoassay (Ag-ELISA) based on a Trypanosoma brucei group-specific monoclonal antibody was evaluated to detect circulating Trypanosoma evansi antigen in horse sera. Three horses and 2 mules were experimentally infected with T. evansi. Circulating antigens were detected on 7 and 21 days postinfection. Antigen levels increased during the course of the illness and remained high even when parasitemia was low or when parasites could not be detected. Antigens were cleared from serum when drug treatment was effective but persisted when it was not. In 6 outbreaks of "mal de caderas" involving 125 horses, T. evansi was found in 78 horses using standard parasite detection methods and antigenemia was detected in 58 of them (74%). The Ag-ELISA sensitivity rate varied between 63% and 100% for the 6 different outbreaks. A combination of Ag-ELISA and parasitologic methods diagnosed a total of 93 infected animals. These results show that the Ag-ELISA test is useful both to diagnose T. evansi and to assess the efficacy of drug treatment in horses.