Sphingomyelins in mosquito saliva reconfigure skin lipidome to promote viral protein levels and enhance transmission of flaviviruses

Many flaviviruses with high pandemic potential are transmitted through mosquito bites. While mosquito saliva is essential for transmission and represents a promising pan-flaviviral target, there is a dearth of knowledge on salivary metabolic transmission enhancers. Here, we show that extracellular vesicle (EV)-derived sphingomyelins in mosquito saliva reconfigure the human cell lipidome to increase viral protein levels, boosting skin infection and enhancing transmission for flaviviruses. Lipids within internalized mosquito EVs enhance infection in fibroblast and immune human primary cells for multiple flaviviruses. Mosquito EV lipids selectively increase viral translation by inhibiting infection-induced endoplasmic reticulum (ER)-associated degradation of viral proteins. Infection enhancement solely results from the sphingomyelins within salivary mosquito EVs that augment human cell sphingomyelin concentration. Finally, EV-lipid co-inoculation exacerbates disease severity in vivo in mouse transmission assays. By discovering and elucidating how metabolic components of mosquito saliva promote transmission of flaviviruses, our study unveils lipids as a new category of targets against vectored transmission.