Studies on Trypanosoma (nannomonas) congolense III. Antigenic variation in three cyclically transmitted stocks.

Cyclical transmission of different variable antigen types of Trypanosoma congolense STIB 228 resulted in the development of metacyclic trypanosome populations which were similar in their variable antigen composition as judged by immunofluorescence and neutralization assays. The variable antigen types present in the ingested bloodstream populations were not found in the metacyclic populations. The bloodstream populations which were obtained from cyclically infected, irradiated (900 rad.) mice contained variable antigen types which were not present in the corresponding metacyclic populations. When derivatives of 2 other stocks of T. congolense, isolated in different area of Tanzania, underwent cyclical development in the tsetse fly, the metacyclic populations of each stock also had a characteristic variable antigen composition. The metacyclic populations of the 3 stocks were, however, completely dissimilar in variable antigen composition. Simultaneous infection of tsetse flies with a mixture of different stocks resulted in the concurrent production of metacyclic trypanosomes which contained the characteristic variable antigen types of each stock. The effect of cyclical transmission on the process of antigenic variation in T. congolense infections is therefore similar to that in T. brucei infections.