The epidemiological significance of some recent findings from research on antigenic variation in trypanosomes.

Antigenic variation in trypanosomes has been recognized for many years and is of epidemiological significance because of the way in which it enables the organisms to resist the natural defence mechanisms of the host and thus to survive in parasitized animals, causing disease and providing a reservoir of further infection. Antigenic variation also limits attempts to use serological methods to type and determine the species of trypanosome isolates, to diagnose trypanosome infections and to immunize against trypanosomiasis.Recent research on antigenic variation in syringe-passaged and cyclically transmitted strains of brucei subgroup trypanosomes has indicated that each strain produces a characteristic basic antigen and a group of predominant variant antigens and that the over-all antigenic character of a strain remains stable under field conditions for periods of at least 2 years. It might be possible to classify isolates of brucei subgroup trypanosomes on the basis of their predominant variant antigens and to determine the species of new isolates by comparing their patterns of variant antigen production with those of fully identified type-strains in rabbits. The significance of results from the application of these findings in the field are discussed. Little progress has been made towards solving the problem of differentiating between antibodies to different species of trypanosomes in the serum of infected animals or with the development of methods of immunization against trypanosomiasis.