Impact of Tiny Targets on Glossina fuscipes quanzensis, the primary vector of Human African Trypanosomiasis in the Democratic Republic of the Congo

Abstract

BackgroundOver the past 20 years there has been a >95% reduction in the number of Gambian Human African trypanosomiasis (g-HAT) cases reported globally, largely as a result of large-scale active screening and treatment programmes. There are however still foci where the disease persists, particularly in parts of the Democratic Republic of the Congo (DRC). Additional control efforts such as tsetse control using Tiny Targets may therefore be required to achieve g-HAT elimination goals. The purpose of this study was to evaluate the impact of Tiny Targets within DRC. Methodology/Principal findingsIn 2015-2017, pre-and post-intervention tsetse abundance data were collected from 1,234 unique locations across three neighbouring Health Zones (Yasa Bonga, Mosango, Masi Manimba). Remotely sensed dry season data were combined with pre-intervention tsetse presence/absence data from 332 locations within a species distribution modelling framework to produce a habitat suitability map. The impact of Tiny Targets on the tsetse population was then evaluated by fitting a generalised linear mixed model to the relative fly abundance data collected from 889 post-intervention monitoring sites within Yasa Bonga, with habitat suitability, proximity to the intervention and intervention duration as covariates. Immediately following the introduction of the intervention, we observe a dramatic reduction in fly catches by > 85% (pre-intervention: 0.78 flies/trap/day, 95% CI 0.676-0.900; 3 month post-intervention: 0.11 flies/trap/day, 95% CI 0.070-0.153) which is sustained throughout the study period. Declines in catches were negatively associated with proximity to Tiny Targets, and while habitat suitability is positively associated with abundance its influence is reduced in the presence of the intervention. Conclusions/SignificanceThis study adds to the body of evidence demonstrating the impact of Tiny Targets on tsetse across a range of ecological settings, and further characterises the factors which modify its impact. The habitat suitability maps have the potential to guide the expansion of tsetse control activities in this area. Authors SummaryThere have been large declines in the number of cases of sleeping sickness as a result of programmes that actively screen and treat the at-risk population. Additional control is needed in areas where the disease persists such as parts of the Democratic Republic of Congo (DRC). The disease is transmitted by tsetse flies, and reducing the tsetse population using Tiny Targets has been shown to control the disease in other countries. Extensive tsetse monitoring has been undertaken in one Health Zone in DRC where Tiny Targets have been deployed. We used these data to gain a better understanding of tsetse habitat, to produce habitat suitability maps, and to subsequently measure the impact of Tiny Targets on the tsetse population. We show that tsetse flies are largely found along rivers and surrounding densely vegetated habitat, with there being a positive relationship between habitat suitability and the numb...

Feasibility of community-based control of tsetse: A pilot project using Tiny Targets in the Democratic Republic of Congo

“…We attempted to measure fly density reduction by placing traps during 48 hours before each Tiny Targets deployment. Not surprisingly, considering the tsetse catch rate in general [27], the catch of tsetse in the small territory of the study sites was too low (total catch = 6 tsetse) to permit statistical analysis as a result the impact of targets on tsetse population is not considered in this paper.…”

“…The second and third deployment were faster to operate as there were fewer Tiny Targets to deploy and committee members had acquired skills and felt more confident (Fig 7). However, when comparing the output to a similar activity operated by the expert-led vector control team the same deployment would have been taken only 3 days [27].…”

Quantifying epidemiological drivers of gambiense human African Trypanosomiasis across the Democratic Republic of Congo

“…Vector control is included in Eq (1) as f T (t), the probability of a fly both hitting a tiny target and subsequently dying at time t. The value of f T (t) is dependent on the population reduction achieved by any vector control performed. For Yasa Bonga health zone, the only health zone in which vector control took place prior to the end of the data collection period, a 90% reduction in tsetse population in the first year after biannual deployment of tiny targets was introduced [27]; more details are given in the SI (S1 Materials and Methods) about the functional form of f T (t), which was originally presented elsewhere [13]. Other tsetse parameters include the pupal stage P V from which new, unfed (teneral) adult flies emerge and it is on this pupal class where we place our density-dependent carrying capacity K, which governs the bounceback speed of the population in the case where f T (t) = 0.…”

Cost-effectiveness of sleeping sickness elimination campaigns in five settings of the Democratic Republic of Congo

“…• Large-scale vector control (VC): twice-yearly deployment of tiny targets to control the population of tsetse, with an assumed 80% reduction after one year, consistent with the lower bound efficacy estimates of field studies [4][5][6]20]. This intervention is assumed to span the areas with ongoing transmission in the previous five years, in keeping with existing operations.…”