Immune priming of orthoflavivirus infected-Aedes aegypti mosquitoes against yellow fever virus

In 2016, 11 travelers infected with yellow fever virus (YFV) were diagnosed in China after returning from Angola. These reported cases outside yellow fever (YF) endemic regions in Africa and South America did not trigger local transmission in this country where ~ 2 billion immunologically naïve people for YF cohabit with YFV-competent Aedes aegypti mosquitoes. We hypothesize that orthoflaviviruses endemic to Asia such as dengue virus (DENV) and Japanese encephalitis virus (JEV) might limit YFV transmission by local Ae. aegypti . Here, we show that YFV transmission by mosquitoes was inhibited after a primo-infection with DENV or JEV. DENV- or JEV-derived small RNAs did not target YFV genome but some mosquito antiviral genes belonging to the siRNA and IMD pathways were differentially expressed following primo-infection. In a context of growing co-circulation of multiple arboviruses, a better understanding of transmission dynamics by vectors is critical to predict emergence and improve preparedness against future pandemics.