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 Ro Tat 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.