Xeno-monitoring the impact of Vector Control on trypanosome transmission in the Forecariah sleeping sickness focus (Guinea)

Author summary In January 2025, the World Health Organization validated the elimination of gambiense human African trypanosomiasis (gHAT) as a public health problem in Guinea. This goal was achieved through a combination of medical and entomological activities over one decade. This strategy was successively implemented in the three gHAT active foci, first in Boffa in 2012, then in Dubreka in 2016 and in Forecariah in 2018. Here, we present the evaluation results of the first three years (2018–2021) of vector control (VC) in the Forecariah focus. VC consisted in the annual deployment of over 5,000 blue insecticide-impregnated tiny targets, mainly in mangrove areas, which are at high risk of Trypanosoma brucei gambiense transmission through tsetse fly bites. Only 18 months after the initial deployment, the apparent density of tsetse flies (ADT) had decreased by 92%. This ADT drop was associated with a significant reduction of the trypanosome infection rates (from 11.5% to 1.2%) in tsetse midguts over the three years of VC. Prior to VC implementation, at least one infected fly was found in 18 of the 31 sentinel traps, whereas only two were positive after three years of monitoring. A pan-trypanosome PCR, used as a molecular xenomonitoring tool, revealed the predominant presence of T. brucei sl., while T. vivax and T. congolense were detected in few tsetse midguts. During this period, HAT prevalence decreased by 76%, highlighting the effectiveness of this combined strategy.