Tsetse Control and Gambian Sleeping Sickness; Implications for Control Strategy

Abstract

BackgroundGambian sleeping sickness (human African trypanosomiasis, HAT) outbreaks are brought under control by case detection and treatment although it is recognised that this typically only reaches about 75% of the population. Vector control is capable of completely interrupting HAT transmission but is not used because it is considered too expensive and difficult to organise in resource-poor settings. We conducted a full scale field trial of a refined vector control technology to determine its utility in control of Gambian HAT.Methods and FindingsThe major vector of Gambian HAT is the tsetse fly Glossina fuscipes which lives in the humid zone immediately adjacent to water bodies. From a series of preliminary trials we determined the number of tiny targets required to reduce G. fuscipes populations by more than 90%. Using these data for model calibration we predicted we needed a target density of 20 per linear km of river in riverine savannah to achieve >90% tsetse control. We then carried out a full scale, 500 km2 field trial covering two HAT foci in Northern Uganda to determine the efficacy of tiny targets (overall target density 5.7/km2). In 12 months, tsetse populations declined by more than 90%. As a guide we used a published HAT transmission model and calculated that a 72% reduction in tsetse population is required to stop transmission in those settings.InterpretationThe Ugandan census suggests population density in the HAT foci is approximately 500 per km2. The estimated cost for a single round of active case detection (excluding treatment), covering 80% of the population, is US$433,333 (WHO figures). One year of vector control organised within the country, which can completely stop HAT transmission, would cost US$42,700. The case for adding this method of vector control to case detection and treatment is strong. We outline how such a component could be organised.

A spatial genetics approach to inform vector control of tsetse flies (Glossina fuscipes fuscipes) in Northern Uganda

“…Moreover, where they do occur, they occur very rarely and at low densities in habitat remote from G. f. fuscipes habitat and human use, making them epidemiologically irrelevant in the geographic region analyzed in this article. Control strategies for G. f. fuscipes have included insecticides sprayed aerially or directly onto cattle, traps, and baited targets (Lindh, Torr, Vale, & Lehane, 2009; Shaw et al., 2013; Tirados et al., 2015; Torr, Hargrove, & Vale, 2005). However, control initiatives implemented to date have experienced some setbacks due to resurgence of tsetse in treated areas because of either residual populations that were not eliminated or immigration from neighboring untreated areas (Aksoy et al., 2013; Opiro et al., 2016; Vreysen, Seck, Sall, & Bouyer, 2013).…”

Predicting the Impact of Intervention Strategies for Sleeping Sickness in Two High-Endemicity Health Zones of the Democratic Republic of Congo

“…In recent years, great improvements to curative drugs and screening programmes have contributed to a substantial decline in disease incidence [1]. In addition, advances in tsetse control have meant that control programmes can use strategies with interventions against both the parasite and vector [2, 3]. …”

“…One such tsetse control method is through the use of insecticidal targets, in particular the recently developed “tiny target” [2, 4]. In areas which have already implemented vector control via tiny targets, a sharp decrease in tsetse abundance has been observed; there has been a reported 80% reduction to tsetse populations in Guinea [3] and 90% reduction in Uganda [2].…”

“…In areas which have already implemented vector control via tiny targets, a sharp decrease in tsetse abundance has been observed; there has been a reported 80% reduction to tsetse populations in Guinea [3] and 90% reduction in Uganda [2]. To complement regular medical surveillance, such tsetse control has the potential to help push towards elimination of this disease.…”

“…Tsetse are attracted to the target, contact it and, in so doing, pick up a lethal dose of insecticide. Trials in Guinea [3], Kenya and Uganda [2] have shown that deployment of tiny targets can reduce densities of tsetse by 70% to >90%. The targets are cheap (∼US$ 1/target) and easy to deploy, hence control of the tsetse population can be achieved at US$ 84/km 2 [19].…”