SUMMARY: During surveys of the prevalence of trypanosomiasis, 37 isolates of trypanosomes of the subgenus were collected over a period of five years from a herd of cattle kept on a farm in an area in Nigeria where human and animal trypanosomiasis is endemic. Thirty-three were typical isolates of but four were unusual in several respects and their identity was uncertain.

The antigenic relationships of the trypanosomes were determined by agglutination tests using antisera to the predominant variant antigens of each isolate. Comparisons of groups of isolates obtained in two of the surveys showed that some of the animals in the herd were infected with antigenically related trypanosomes. Four isolates obtained in one survey had antigens in common and probably belonged to one trypanosome strain, while 26 isolates obtained in another survey seemed to have been derived from three different strains. At least ten animals examined in the latter survey were infected with two strains of at the same time. Comparisons of trypanosomes obtained in successive surveys showed that one isolate was very closely related to four isolates obtained from different animals two years later. Agglutination and neutralization tests, and a study of variant antigen production by clones prepared from the first isolate and one of the later group of four isolates, established the antigenic similarity of these trypanosomes and provided direct evidence of the long-term antigenic stability of a trypanosome strain under field conditions. Apart from this notable exception, there was little antigenic relationship among the trypanosomes isolated from year to year and at least seven antigenically distinct strains of were isolated from the herd in the five-year observation period.


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