Impact of a small-scale tsetse fly control operation with deltamethrin impregnated "Tiny Targets" on tsetse density and trypanosomes' circulation in the Campo sleeping sickness focus of South Cameroon.

BACKGROUND: Significant progress has been made towards African sleeping sickness elimination in the last decade. Indeed, the World Health Organization (WHO) global goal of eliminating the chronic form of the disease as a public health problem was achieved in 2020 (i.e., < 2,000 new cases per year). Vector control has played an important role in achieving this goal. In this study, we evaluated the impact of the insecticide impregnated Tiny Targets on tsetse fly densities and their infection rates with Trypanosoma spp in the Campo sleeping sickness focus of South Cameroon. METHODS: The study site was divided into two areas: (i) the south-west experimental area, which included vector control, and (ii) the eastern part as the non-intervention area. After compiling the baseline entomological data (tsetse densities and trypanosome infection rates), around 2000 Tiny Targets were deployed in the South-West area and replaced every six months for two years. Post-intervention surveys were conducted every six months to determine tsetse densities and levels of trypanosome infections with PCR-based methods. RESULTS: Following the intervention, tsetse mean catches decreased by 61% after six months, and up to 73% after twelve months (pre-intervention: 2.48 flies/trap/day, 95%CI [1.92-3.14]; 12-months post-intervention: 0.66 tsetse/trap/day, 95%CI [0.42-0.94]). This decrease was not sustained after 18 months, and the mean catch doubled compared to that after 12 months. After 24 months, the mean catches still increased by 17% (18 months: 1.45 tsetse/trap/day, 95%CI [1.07-1.90] and 24 months: 1.71 tsetse/trap/day, 95%CI [1.27-2.24]). In the non-intervention area, a variation in tsetse catches was observed during the two years, with a general increase from 2.43 [0.73-5.77] to 3.64 [1.47-7.70] tsetse/trap/day. In addition, trypanosome infection rates dropped by 75% in both areas (P-value < 0.001) from 21.20% to 5.06% and from 13.14% to 3.45% in intervention and control areas respectively. CONCLUSION: Tiny targets have proven useful in reducing tsetse population densities and trypanosome infection rates, providing evidence for the integration of this tool in current strategies towards trypanosomiasis elimination in Campo. The non-sustained decrease of tsetse densities after one year may indicate reinvasions from neighbouring breeding sites or that the intervention area was not large enough. Our results show the need to scale up by accessing difficult breeding sites and extend the tiny targets to the whole transborder focus.

Environmental mutations in the Campo focus challenge elimination of sleeping sickness transmission in Cameroon.

Sleeping sickness is still prevalent in Campo, southern Cameroon, despite the efforts of World Health Organization and the National Control Programme in screening and treating cases. Reducing disease incidence still further may need the control of tsetse vectors. We update entomological and parasitological parameters necessary to guide tsetse control in Campo. Tsetse flies were trapped, their apparent densities were evaluated as the number of flies captured per trap per day and mapped using GIS tools. Polymerase chain reaction based methods were used to identify their trypanosome infection rates. Glossina palpalis palpalis was the dominant vector species representing 93.42% and 92.85% of flies captured respectively during the heavy and light dry seasons. This species presented high densities, that is, 3.87, 95% CI [3.84-3.91], and 2.51, 95% CI [2.49-2.53] flies/trap/day in the two seasons. Moreover, 16.79% (of 1054) and 20.23% (of 1132 flies) were found infected with at least 1 trypanosome species for the 2 seasons respectively, Trypanosoma congolense being the most prevalent species, and Trypanosoma. brucei gambiense identified in 4 samples. Tsetse flies are abundant in Campo and present high trypanosome infection rates. The detection of tsetse infected with human trypanosomes near the newly created palm grove show workers' exposition. Tsetse densities maps built will guide vector control with 'Tiny Targets'.