The epidemiological relevance of trypanosome strain variation

The study of strain variation in T.b. rhodesiense has yielded a lot of information which suggests that these trypanosomes are a sub-set of the stocks circulating in tsetse and non human hosts and that each focus constitutes a separate set of human infective stocks. These conclusions remain to be fully established by extensive studies in specific foci. Whether the maintenance of these foci or the expansion of them into epidemics is dependent on variation in the trypanosoma stocks generated by mutation or genetic exchange is unanswered. In order to examine such questions, detailed long-term studies using large numbers of isolates are needed. The analysis of strain variation using existing methods requires considerable manpower and equipment and suffers from the need for growth of trypanosomes in laboratory animals with resultant selection of the stocks under study. The question of whether strain variation in T.b. rhodesiense is epidemiologically relevant remains unanswered, variation certainly occurs but the existing studies are not able to answer this question. It is possible that this question could be answered by detailed studies in two or more foci over a long period using new reagents for the detection of variation (e.g. monoclonal antibodies), large trypanosome stock collections and the measurement of parameters such as virulence, tsetse transmissibility etc.