Comparing Ivermectin susceptibility in wild-derived and laboratory-reared Aedes and Anopheles larvae: Preliminary study on selecting for resistance mechanisms

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Ouedraogo, Cheick Oumar W. | Sougue, Emmanuel, Daouda | Sagna, André, Barembaye | Traoré, Olive | Soma, Dieudonné, Diloma | Pooda, Sié Hermann | Zéla, Lamidi | Le Lamer Deschamps, Sophie | Ndiaye, Mady | Niang, E.H. Mamadou | Mouline, Karine | Somé, Fabrice, A. | Dabiré, Roch Kounbobr

Edité par CCSD -

International audience. Introduction and ObjectivesAdministering ivermectin to humans and livestock renders their blood toxic for mosquitoes like Anopheles and Aedes, offering a promising approach for controlling these vectors. However, the impact of such treatment on larval stages exposed to the drug through contaminated breeding sites is not fully understood. This study looked at how ivermectin affects the development of Aedes and Anopheleslarvae.Materials and MethodsWe exposed laboratory-reared (Anopheles gambiae Kisumu and Aedes aegypti Bora Bora) and wild- derived (Anopheles coluzzii VK5 and Aedes aegypti Bobo) larvae to ivermectin concentrations ranging from 1 to 100 ng/ml for 24h, and transferred surviving larvae into free-ivermectin medium to monitor development until adult stage. Parameters measured were : survival, pupation dynamics, emergence rates, and fecundity of the adult females. Ivermectin effects were characterized by comparison with larvae raised in control medium.ResultsData indicated that highest ivermectin concentrations (100, 75, and 50 ng/ml) reduced larval survival by over 50% within 24 to 48 hours post-exposure, with varying effects across different strains. Wild-derived larvae showed lower susceptibility to ivermectin compared to laboratory larvae for both Anophelesand Aedes species. The concentrations leading to 50% larval mortality (4-day-LC50) were 3.65 and 1.86 ng/ml for Anopheles VK5 and Kisumu strains, and 15.60 and 2.56 ng/ml for Aedes Bobo and Bora Bora strains, respectively. The transition from larval to adult stage was significantly affected, particularly in the Kisumu strain (p = 0.001). No significant effects on the number of laid eggs were observed across different strains.Discussion and ConclusionThese data showed how lab-raised and wild-derived Anopheles and Aedes larvae are affected differently by ivermectin, highlighting potential implications for vector control strategies. Further investigations are planned to understand potential existing mechanisms allowing wild-derived larvae to better survive to ivermectin exposition than laboratory ones.

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