Detection of Trypanosoma brucei rhodesiense in animals from sleeping sickness foci in East Africa using the serum resistance associated (SRA) gene

The human serum resistance associated (SRA) gene has been found exclusively in Trypanosoma brucei rhodesiense, allowing the unequivocal detection of this pathogen in reservoir hosts and the tsetse vector without recourse to laborious strain characterisation procedures. We investigated the presence of the SRA gene in 264 T. brucei ssp. isolates from humans, domestic animals and Glossina pallidipes from foci of human trypanosomiasis in Kenya and Uganda. The SRA gene was present in all isolates that were resistant to human serum, and absent from all serum sensitive isolates tested. Further, the gene was present in all isolates that had previously been shown to be identical to human infective trypanosomes by isoenzyme characterisation. The SRA gene was detected in isolates from cattle, sheep, pigs, dog, reedbuck, hyena and G. pallidipes from sleeping sickness foci, but was not found in Trypanosoma evansi or in Trypanosoma brucei gambiense isolates. The present study indicates that the SRA gene may be invaluable in detecting and differentiating T. brucei rhodesiense from other T. brucei ssp. in reservoir hosts and tsetse.