Landscape genetics of Simulium blackflies from Ghana. Synthesising environmental, epidemiological, and genetic data to assist decision making for onchocerciasis elimination

Blackflies in the genus Simulium are vectors of a filarial nematode parasite that causes the disease onchocerciasis, or River blindness. Over 100 million people in Africa are at risk of contracting onchocerciasis, which can cause debilitating symptoms including skin lesions, blindness, and epilepsy. Efforts to control the disease focused on mass drug administration of ivermectin, but as the goal has shifted to elimination of transmission, there has been renewed interest in disrupting blackfly breeding sites, in identifying routes for long-distance blackfly migration that might spread the parasite, and in quantifying differences in species transmission capabilities. We have used a landscape genetics framework to understand the relationship between environmental features and measures of gene flow of the filarial parasite Onchocerca volvulus and its intermediate host and vector, blackflies of the genus Simulium. We obtained samples from the ecological transition region separating the savannah and forest ecological regions of Ghana, where the transmission of O. volvulus has persisted despite almost half a century of onchocerciasis control efforts. We identify areas with higher ecological suitability for parasite and vector gene flow, which might help us gain insights into identifying transmission zones for onchocerciasis. Furthermore, this framework is translatable to other endemic areas and vector-borne diseases.