T. b. gambiense; evidence of absence in NW Uganda

Tue16  Apr12:51pm(3 mins)
Renold C9


L J CunninghamJ K LingleyM J LehaneS J Torr
1 Liverpool School of Tropical Medicine , UK



Around the turn of the century the last major epidemic of Gambian sleeping sickness was being brought to an end thanks to a concerted effort to control the disease. The prevalence of disease has since gradually decreased with the number of new cases being reported, per year, now numbering 1,420. This success indicates that there is a good chance that the disease could be eliminated, as a public health problem, by 2020. Although close to achieving this goal there may still be obstacles blocking the road to success, chief amongst these is the still unanswered question of cryptic reservoirs. Previous studies have found T. b. gambiense in both wild and domestic animals, however, transmission of disease from animals to humans, via the tsetse vector has not been proven. Finding positive zoonotic hosts for T. b. gambiense in an area of control would indicate that the current strategy of surveillance of the human population may not be enough. Our work was carried out in the NW of Uganda, a historic sleeping sickness focus, that had seen a reduction of the disease from >100 prior to 2010 to current levels of <5 new cases reported annually, making it an ideal example of a setting approaching elimination.


To carry out a large-scale surveillance campaign on local cattle, pigs and tsetse in the historic sleeping sickness foci of Arua, Maracha and Koboko in NW Uganda, using molecular methods to screen for T. b. gambiense.


From the districts of Arua, Maracha and Koboko a total of 2088 cattle, 400 pigs and 2,184 flies were sampled and screened for T. b. gambiense using species and sub-species specific PCR assays. A sub-sample of positives underwent sequencing to better characterise the trypanosomes detected. The Cattle were enrolled as part of a larger, vector control study, while the pigs were sampled from communities with a history of sleeping sickness that were located outside of tsetse control areas. The tsetse were caught from four traps deployed in Koboko along the Kochi river.


Initial screening of samples with the TBR-primer found that 1.9% (95% CI≤1.9-2.5) of cattle, 6.2% (95% CI≤4.1-9.1) of pigs and 1.8% (95% CI≤1.3-2.5) of tsetse were positive for T. brucei s.l.. Further analysis revealed that not all the T. brucei s.l. positive samples contained enough DNA for the detection of the single copy TgsGP gene used to characterise the T. b. gambiense, with ~40% of positive samples lacking sufficient DNA. Of the cattle and pig samples with a sufficient amount of DNA all failed to produce a PCR product indicative of T. b. gambiense, but of the tsetse positive samples 16 produced a faint band of 281 bp in size. When a sub-sample were sequenced all returned the same sequence, however this sequence failed to match the reference sequence of T. b. gambiense in both length and composition.


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