A Study of the Antigenic Relationships of Isolates of Trypanosoma brucei Collected from a Herd of Cattle Kept in One Locality for Five Years

Abstract

During surveys of the prevalence of trypanosomiasis, 37 isolates of trypanosomes of the subgenus Tr.ypanozoon 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 Trypanosoma brucei 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 Trypanosoma brucei 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 T. brucei were isolated from the herd in the five-year observation period.

Antigenic variation in its biological context

“…While differences in growth rates of antigenically different cloned populations of brucei in the same host have been described, little is known about possible variable antigen associated differences in host susceptibility. However, as it is known that even brucei and , which are nominally infective to mice, can be very difficult to establish from field isolates (Gray 1970;Goedblad et al 1973) the possibility that there is selection for particular variants that are capable of infecting laboratory rodents should be considered, as this clearly imposes a bias on all subsequent experiments.…”