Viruses transmitted by Aedes mosquitoes are an increasingly important global cause of disease. Defining common determinants of host susceptibility to this large group of het- erogenous pathogens is key for informing the rational design of panviral medicines. Infection of the vertebrate host with these viruses is enhanced by mosquito saliva, a complex mixture of salivary-gland-derived factors and microbiota. We show that the enhancement of infection by saliva was dependent on vascular function and was inde- pendent of most antisaliva immune responses, including salivary microbiota. Instead, the Aedes gene product sialokinin mediated the enhancement of virus infection through a rapid reduction in endothelial barrier integrity. Sialokinin is unique within the insect world as having a vertebrate-like tachykinin sequence and is absent from nonvector competent Anopheles mosquitoes, whose saliva was not proviral and did not induce sim- ilar vascular permeability. Therapeutic strategies targeting sialokinin have the potential to limit disease severity following infection with Aedes-mosquito-borne viruses
