Résumé
Uganda is the only country where the chronic and acute forms of human
African Trypanosomiasis (HAT) or sleeping sickness both occur and are
separated by < 100 km in areas north of Lake Kyoga. In Uganda,
Glossina fuscipes fuscipes is the main vector of the Trypanosoma parasites
responsible for these diseases as well for the animal African
Trypanosomiasis (AAT), or Nagana. We used highly polymorphic
microsatellite loci and a mitochondrial DNA (mtDNA) marker to provide fine
scale spatial resolution of genetic structure of G. f. fuscipes from 42
sampling sites from the northern region of Uganda where a merger of the
two disease belts is feared. Based on microsatellite analyses, we found
that G. f. fuscipes in northern Uganda are structured into three distinct
genetic clusters with varying degrees of interconnectivity among them.
Based on genetic assignment and spatial location, we grouped the sampling
sites into four genetic units corresponding to northwestern Uganda in the
Albert Nile drainage, northeastern Uganda in the Lake Kyoga drainage,
western Uganda in the Victoria Nile drainage, and a transition zone
between the two northern genetic clusters characterized by high level of
genetic admixture. An analysis using HYBRIDLAB supported a hybrid swarm
model as most consistent with tsetse genotypes in these admixed samples.
Results of mtDNA analyses revealed the presence of 30 haplotypes
representing three main haplogroups, whose location broadly overlaps with
the microsatellite defined clusters. Migration analyses based on
microsatellites point to moderate migration among the northern units
located in the Albert Nile, Achwa River, Okole River, and Lake Kyoga
drainages, but not between the northern units and the Victoria Nile
drainage in the west. Effective population size estimates were variable
with low to moderate sizes in most populations and with evidence of recent
population bottlenecks, especially in the northeast unit of the Lake Kyoga
drainage. Our microsatellite and mtDNA based analyses indicate that G. f.
fuscipes movement along the Achwa and Okole rivers may facilitate
northwest expansion of the Rhodesiense disease belt in Uganda. We
identified tsetse migration corridors and recommend a rolling carpet
approach from south of Lake Kyoga northward to minimize disease dispersal
and prevent vector re-colonization. Additionally, our findings highlight
the need for continuing tsetse monitoring efforts during and after
control.