Epidemiology and diagnosis of African trypanosomiasis using DNA probes

The accurate identification of trypanosome species has been a challenging problem in the epidemiology of African trypanosomiasis, both human and animal. The last 10 years have seen great progress through the application of deoxyribonucleic acid (DNA) probe technology, although this has also revealed greater complexity than supposed. While a single repetitive DNA probe can identify all members of the subgenus Trypanosoma (Trypanozoon), including the human pathogens T. brucei gambiense and T. b. rhodesiense as well as the non-tsetse-transmitted trypanosomes T. evansi and T. equiperdum, at least 6 probes are needed to distinguish members of the subgenus Nannomonas, in which only 2 species, T. congolense and T. simiae, were previously recognized. Similarly, the subgenus Duttonella appears to consist of more than one species. Use of this battery of DNA probes to identify the trypanosomes carried by tsetse flies in the field has yielded some surprises about the accuracy (or inaccuracy) of previous identification methods. An unexpectedly high prevalence of mixed infections has been found in all the field studies carried out so far. The large number of infections that remain unidentified by the available probes suggests the existence of other, as yet unknown, trypanosome species. Limited use of the polymerase chain reaction has been made for diagnosis of human and animal trypanosomiasis, due to its high cost.