Mosquito Saliva Serine Protease Enhances Dissemination of Dengue Virus into the Mammalian Host

Dengue virus (DENV), a flavivirus of global importance, is transmitted to humans by mosquitoes. In this study, we developed in vitro and in vivomodels of saliva-mediated enhancement of DENV infectivity. Serine protease activity in Aedes aegypti saliva augmented virus infectivity in vitro by proteolyzing extracellular matrix proteins, thereby increasing viral attachment to hepa-ran sulfate proteoglycans and inducing cell migration. A serine protease inhibitor reduced saliva-mediated enhancement of DENV in vitro and in vivo, marked by a 100-fold reduction in DENV load in murine lymph nodes. A saliva-mediated infectivity enhancement screen of fractionated salivary gland extracts identified serine protease CLIPA3 as a putative cofactor, and short interfering RNA knockdown of CLIPA3 in mosquitoes demonstrated its role in influencing DENV infectivity. Molecules in mos-quito saliva that facilitate viral infectivity in the vertebrate host provide novel targets that may aid in the prevention of disease. Flaviviruses cause substantialmorbidity andmortality through-out the world. Dengue virus (DENV), transmitted by Aedes aegypti mosquitoes, causes the most significant public health im-pact (1). When A. aegypti probe during a blood meal, saliva is injected primarily into host extravascular dermal spaces (2, 3). To efficiently feed, A. aegyptimust overcome host barriers, including the physiological responses elicited by hemostatic and inflamma