Expression of RoTat 1.2 cross-reactive variable antigen type in Trypanosoma evansi and T. equiperdum

The variable antigen type (VAT) RoTat 1.2 has been cloned from a T evansi strain, isolated in 1982 from a water buffalo in Indonesia. All T evansi isolates hitherto tested express this VAT. In a study on the differential diagnosis of T equiperdum and T evansi in horses, we investigated serological evidence for the expression of RoTat 1.2 in 11 T evansi and six T equiperdum populations originating from Asia, Europe, Africa, and the Americas. Preinfection sera and sera of days 7, 14, 25, and 35 post-infection (p.i.) were analyzed for the presence of antibodies reactive with RoTat 1.2 in immune trypanolysis, ELISA/T. evansi and CATT/T evansi. Within the duration of the experiment, all rabbits infected with T evansi became positive in the three serological tests. Five out of six rabbits infected with T equiperdum also became positive in the three tests. Only one T equiperdum strain (the OVI strain from South Africa) did not induce the production of antibodies reactive with RoTat 1.2 and thus might not contain or express a VSG that shares epitopes similar to those on the RoTat 1.2 VSG. The data lead to the conclusion that T equiperdum can express VSGs containing epitopes serologically similar to those in the T evansi RoTat 1.2 VAT. This explains, in part, why the antibody detection tests based on RoTat 1.2 VSG cannot reliably distinguish between the infections caused by T evansi and those caused by T equiperdum. There are no data that contradict the possibility that the putative T equiperdum strains, which express VSGs with epitopes similar to those on RoTat 1.2, are actually T evansi.