Trypanosoma brucei: identification of trypanosomes with genotypic similarity to human infective isolates in tsetse isolated from a region free of human sleeping sickness.

In previous work, we have developed a molecular method that defines genotypes of Trypanosoma brucei and allows distinction of the human-infective subspecies T. b. rhodesiense from the non-human-infective T. b. brucei without recourse to measurement of resistance to lysis by human serum. Using this approach, we are also able to determine the geographical range of specific genotypes associated with a particular focus. In this study, we have characterised T. brucei isolates collected from tsetse in a region where human sleeping sickness has never been reported and which is some 500 km from the Busoga sleeping sickness focus of Uganda. We show that some of the trypanosome isolates taken from tsetse in this region have considerable genotypic similarity to trypanosomes from the Busoga focus, demonstrating a surprisingly wide dispersal of these trypanosome genotypes. Furthermore, the similarity of these genotypes to human-infective trypanosomes in the Busoga focus suggest the possible circulation of human-infective trypanosomes in this location. We also demonstrate that the genetic diversity in trypanosomes isolated from tsetse is significantly higher than that in those isolated from humans, confirming other studies that show that there exists a significant restriction in the range of genotypes that can be transmitted to humans.