Tsetse fly ecology and risk of transmission of African trypanosomes related to a protected forest area at a military base in the city of Abidjan, Côte d'Ivoire.

African trypanosomoses, whose pathogens are transmitted by tsetse flies, are a threat to animal and human health. Tsetse flies observed at the military base of the French Forces in Côte d'Ivoire (FFCI base) were probably involved in the infection and death of military working dogs. Entomological and parasitological surveys were carried out during the rainy and dry seasons using "Vavoua" traps to identify tsetse fly species, their distribution, favorable biotopes and food sources, as well as the trypanosomes they harbor. A total of 1185 Glossina palpalis palpalis tsetse flies were caught, corresponding to a high average apparent density of 2.26 tsetse/trap/day. The results showed a heterogeneous distribution of tsetse at the FFCI base, linked to more or less favorable biotopes. No significant variation in tsetse densities was observed according to the season. The overall trypanosomes infection rate according to microscopic observation was 13.5%. Polymerase chain reaction (PCR) analyses confirmed the presence of Trypanosoma vivax and T. congolense forest type, responsible for African animal trypanosomosis. Our findings suggest that there is a risk of introduction and transmission of T. brucei gambiense, responsible for human African trypanosomiasis, on the study site. This risk of transmission of African trypanosomes concerns not only the FFCI base, but also inhabited peripheral areas. Our study confirmed the need for vector control adapted to the eco-epidemiological context of the FFCI base.

Title: Écologie des mouches tsé-tsé et risque de transmission des trypanosomes africains lié à une zone forestière protégée dans une base militaire de la ville d'Abidjan, Côte d'Ivoire. Abstract: Les trypanosomoses africaines, dont les agents pathogènes sont transmis par les mouches tsé-tsé, constituent une contrainte pour la santé animale et humaine. Des mouches tsé-tsé observées dans la base militaire des Forces françaises en Côte d'Ivoire (base FFCI) ont probablement été impliquées dans l'infection et la mort de chiens militaires. Des enquêtes entomologiques et parasitologiques ont été menées pendant la saison pluvieuse et la saison sèche à l'aide de pièges "Vavoua" afin d'identifier les espèces de mouches tsé-tsé, leur distribution, les biotopes favorables et leur source de nourriture ainsi que les trypanosomes qu'elles hébergent. Au total 1185 mouches tsé-tsé de l'espèce Glossina palpalis palpalis ont été capturées, ce qui correspond à une densité apparente moyenne élevée de 2,26 tsé-tsé/piège/jour. Les résultats ont montré une distribution hétérogène des tsé-tsé dans la base FFCI en lien avec des biotopes plus ou moins favorables. Aucune variation significative des densités de tsé-tsé n'a été observée en fonction de la saison. Le taux d'infection global par les trypanosomes était de 13,5 % selon l'observation microscopique. Les analyses PCR ont confirmé la présence de Trypanosoma vivax et T. congolense type forêt, responsable de la trypanosomose animale africaine. Nos résultats suggèrent qu'il existe un risque potentiel d'introduction et de transmission de T. brucei gambiense responsable de la trypanosomiase humaine africaine dans la zone d'étude. Ce risque de transmission des trypanosomes africains concerne non seulement l'intérieur de la base FFCI, mais aussi les espaces périphériques habités. Notre étude a confirmé la nécessité de mener une lutte antivectorielle adaptée au contexte éco-épidémiologique de la base FFCI.

Use of vector control to protect people from sleeping sickness in the focus of Bonon (Côte d'Ivoire).

BACKGROUND: Gambian human African trypanosomiasis (gHAT) is a neglected tropical disease caused by Trypanosoma brucei gambiense transmitted by tsetse flies (Glossina). In Côte d'Ivoire, Bonon is the most important focus of gHAT, with 325 cases diagnosed from 2000 to 2015 and efforts against gHAT have relied largely on mass screening and treatment of human cases. We assessed whether the addition of tsetse control by deploying Tiny Targets offers benefit to sole reliance on the screen-and-treat strategy. METHODOLOGY AND PRINCIPAL FINDINGS: In 2015, we performed a census of the human population of the Bonon focus, followed by an exhaustive entomological survey at 278 sites. After a public sensitization campaign, ~2000 Tiny Targets were deployed across an area of 130 km2 in February of 2016, deployment was repeated annually in the same month of 2017 and 2018. The intervention's impact on tsetse was evaluated using a network of 30 traps which were operated for 48 hours at three-month intervals from March 2016 to December 2018. A second comprehensive entomological survey was performed in December 2018 with traps deployed at 274 of the sites used in 2015. Sub-samples of tsetse were dissected and examined microscopically for presence of trypanosomes. The census recorded 26,697 inhabitants residing in 331 settlements. Prior to the deployment of targets, the mean catch of tsetse from the 30 monitoring traps was 12.75 tsetse/trap (5.047-32.203, 95%CI), i.e. 6.4 tsetse/trap/day. Following the deployment of Tiny Targets, mean catches ranged between 0.06 (0.016-0.260, 95%CI) and 0.55 (0.166-1.794, 95%CI) tsetse/trap, i.e. 0.03-0.28 tsetse/trap/day. During the final extensive survey performed in December 2018, 52 tsetse were caught compared to 1,909 in 2015, with 11.6% (5/43) and 23.1% (101/437) infected with Trypanosoma respectively. CONCLUSIONS: The annual deployment of Tiny Targets in the gHAT focus of Bonon reduced the density of Glossina palpalis palpalis by >95%. Tiny Targets offer a powerful addition to current strategies towards eliminating gHAT from Côte d'Ivoire.