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Reducing densities of zoophagous Anopheles by treating cattle with an innovative formulation of Ivermectin while preserving the environment : a One-Health approach
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Edité par CCSD -
International audience. In rural Sudano-Sahelian zones, livestock live close to humans and are alternative blood sources for Anopheles vectors of Plasmodium, even the most anthropophagic. Thus, vectors remain at densities sustaining transmission of the parasite, despite massive coverage using conventional control tools. In Burkina Faso, we work on a holistic approach: treating livestock with ivermectin to render animal blood toxic to Anopheles, hence promoting both human and animal health. Yet, approved ivermectin formulations are of too short remanence to impact malaria incidence. In this context, Long-Acting Ivermectin Formulations (LAIFs) that deliver, upon a single injection, efficient ivermectin concentrations spanning the transmission season would represent substantial advantage, but would raise ecotoxicological concerns for already fragile agro-ecosystems. In the Anivermate project, a LAIF candidate targeting more than 6 months efficacy was designed using the BEPO® technology (IVM-BEPO®) and administered at 2.4 mg/kg to local cattle. Efficacy against wild-derived Anopheles coluzzii was determined through survival experiments and compared with that of an already approved formulation injected monthly at 0.4 mg/kg. Data were used in a population model to predict effectiveness, according to Anopheles trophic preference, infectious status, and human-animal ratio in the villages. Plasma and fecal ivermectin concentrations were measured and risks for the environment explored (thorough bibliography, dissipation in feces and soil sorption experiments). A single injection of the IVM-BEPO® is mosquitocidal for over 6 months, with median Anopheles lifespan being 3-5 days. A single injection would reduce infectious Anopheles populations by 50-90% in all tested scenarios. By comparison, efficacy of a single injection of approved formulation lasts 14 days. Risks for agro-ecosystems are likely, notably through toxicity to coprophagic insects. However, local dissipation tools (fosses fumières) and agro-pastoral practices would be efficient mitigation tools. Hence, our integrative and holistic approach could reach sustainability, while providing efficient tool to combat malaria.
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