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Isolates of T. gambiense were collected in different localities in Nigeria by inoculating lymph node biopsy specimens from sleeping sickness patients with newly-diagnosed, untreated infections intraperitoneally into white rats. 97 out of 122 rats inoculated with material from different patients developed trypanosome infections. The trypanosomes were typical isolates of T. gambiense and their virulence for young adult rats (80–100 g.) was invariably low. Antigens for use in agglutination tests were prepared from lines of 48 isolates, which had been adapted to animals by repeated passage in nursling rats, and agglutinating antisera to the predominant variant antigens of the trypanosomes were prepared in rabbits. A study of antigenic variation in 2 of the rodent-adapted isolates during infections in rabbits, and of the reactions of antisera to other adapted isolates, led to the identification of 19 serologically different populations of trypanosomes among antigens prepared from 34 of the isolates. In several instances groups of 2 or 4 isolates, and in 1 instance a group of 6 isolates, adapted during maintenance in nursling rats in a similar antigenic form. A survey of the distribution of antigens representing the 19 serologically different types of trypanosomes indicated that isolates of T. gambiense from all parts of Nigeria produced at least 7 variant agglutinogenic antigens in common, a further 9 antigens were widely, but less uniformly, distributed among isolates from different areas, and the remaining 3 antigens were produced only by isolates collected at centres situated in the south and east of the sleeping sickness area. The isolates were grouped together as a single trypanosome strain in view of their capacity to produce similar variant antigens, but they were divided into 2 substrains on the basis of ability to produce the 3 antigens with a restricted geographical distribution. Antigens prepared from rodent-adapted lines of different isolates of T. gambiense were agglutinated by sera from sleeping sickness patients, and from rats and rabbits infected with T. gambiense inoculated in lymph node biopsy specimens taken directly from sleeping sickness patients. These results demonstrated the similarity of the antigens of rodent-adapted isolates of T. gambiense to those of unadapted field isolates of the trypanosome, and fully supported the classification of the adapted isolates into 2 geographically distinct substrains.
A. R. Gray (1972) studied this question.