Worldwide survey reveals lower susceptibility of African Aedes aegypti mosquitoes to diverse strains of Zika virus

Zika virus (ZIKV) is a flavivirus mainly transmitted to humans through the bite of infected Aedes aegypti mosquitoes. First isolated in Uganda in 1947, ZIKV was shown to circulate in enzootic sylvatic cycles in Africa and Asia for at least half a century before the first reported human epidemic occurred in 2007 on the Pacific island of Yap, Micronesia. Subsequently, larger ZIKV outbreaks were recorded in French Polynesia and other South Pacific islands during 2013-2014. In 2015, ZIKV reached Brazil from where it rapidly spread across the Americas and the Caribbean, causing hundreds of thousands of human cases. The factors that have fueled the explosiveness and magnitude of ZIKV emergence in the Pacific and the Americas are poorly understood. Reciprocally, the lack of major human epidemics of ZIKV in regions with seemingly favorable conditions, such as Africa or Asia, remains largely unexplained. To evaluate the potential contribution of vector population diversity to ZIKV epidemiological patterns, we established dose-response curves for eight field-derived Ae. aegypti populations representing the global range of the species, following experimental exposure to six low-passage ZIKV strains spanning the current viral genetic diversity. Our results reveal that African Ae. aegypti are significantly less susceptible than non-African Ae. aegypti across all ZIKV strains tested. We suggest that low susceptibility of vector populations may have contributed to prevent large-scale human transmission of ZIKV in Africa.