Serological diagnosis of Trypanosoma evansi (Steel, 1885) in horses using a direct agglutination test.

A direct agglutination test is described to diagnose 'Mal de Caderas' caused by Trypanosoma evansi. The antigen used was a suspension of trypsin-treated parasites stabilized with formalin. The test was evaluated in horses with both natural and experimental infections. Test sensitivity and specificity were 94 and 97%, respectively. Treatment of serum with 2-mercaptoethanol before testing permitted the differentiation of IgM and IgG antibodies, and possible differentiation of current infection from past exposure to the parasite. The antigen was stable over a 6-month evaluation period and also showed good reproducibility between different batches. The direct agglutination test is proposed as another tool for diagnosis of T. evansi in horses, both for detecting clinical cases and for seroepidemiological studies.