Studies on the sequence of variable antigen types in ponies infected with a clone of Trypanosoma evansi

The sequential appearance of variable antigen types (VATs) of a clone of Trypanosoma evansi was studied in four ponies. Using luminol-dependent chemiluminescence, VAT populations which had been isolated from parasitemic peaks of single ponies, were tested for specificity with serum samples collected from other ponies. When antibody activity was demonstrated in a combination of trypanosomes and serum, it was concluded that a major VAT appeared in common. In the serum of all animals antibody activity was demonstrated to all VAT populations isolated from the other ponies during the first 4 weeks of infection, indicating that up to this moment in all four animals the same major VATs developed. The sequence of major VATs was very similar in all ponies. Several parasitemic waves consisted of more than one major VAT, and in another pony a certain major VAT developed either in the same or in a neighbouring wave of the parasitemia.