Antigenic variation in Trypanosoma evansi: variable antigen type (VAT) composition of first relapse populations in mice.

The variable antigen type (VAT) composition of first relapse populations developing in mice infected with 11 VAT populations of a stock of T. evansi was shown to be independent of the infecting VAT. Trypanosomes representing three of the VATs were found in all relapse populations resulting from infection with each VAT. A further seven VATs were detected in at least one relapse population from each VAT. These 10 VATs had previously been classed as predominant VATs from studies on VAT development in rabbits, sheep and goats. It is probable, therefore, that the VAT composition of first relapse populations can be used as a basis for the classification of T. evansi stocks into serodemes according to their predominant VAT repertoires.