The application of serological, biochemical and molecular techniques for the differentiation of stocks of Trypanosoma evansi

Throughout its distribution range T. evansi consists of a large number of morphologically identical population that differ significantly in various biological characters such as host range, virulence and pathogenecity, and drug sensitivity. Stock that share common features are termed demes (Hoare, 1972). Commonly described demes of T. evansi include: Serodemes-which represent immunologically distinct stocks; Xenodemes - distinguished by their host preferences; Clinodemes-respresented by populations that have characteristics such as virulence and pathogenicity that change over the areas of geographical distribution of the parasite; Zymodemes-differ in the isoenzyme banding pattern of one or more enzymes; Schizodemes-are based on DNA diversity. The ability to identify different demes of trypanosomes has practical application in epidemiology and disease control. The ability to associate populations with certain characteristics such as area of origin or host species can help in tracing outbreaks of disease while the identification of drug resistant populations can help in making the most of dwindling trypanocidal drug resources. A number of technologies of been applied to the analysis of diversity among stocks of T. evansi, notably isoenzyme banding pattern analysis, predominant variant antigen reportoire analysis and, most recently, nucleic acid analysis. The results from most of these studies indicate that T. evansi shows far less genetic diversity overall than the tsetsetransmitted trypanosomes and that different stocks should respond similarly to new approaches to control. Changes in certain parts of the genome that lead to the emergence of drug-resistant populations are probably the most important aspects of diversity in T. evansi at present. As molecular techniques for stock characterisation become more widely available along with an ever increasing range of DNA probes it is likely that this technology will continue to play a major role in the differentiation of trypanosome stocks. It is also likely, however that classifications based on carbohydrate and lipid analysis will be applied to stock characterisation in the near future now that such analyses can be carried out in a similar way to DNA sequencing