Increased Mosquito Midgut Infection by Dengue Virus Recruitment of Plasmin Is Blocked by an Endogenous Kazal-type Inhibitor

Dengue symptoms include alteration of blood coagulation and fibrinolysis, causing severe hemorrhage and death. Here, we demonstrate that higher concentration of plasmin, the human fibrinolytic factor, in blood meal enhances dengue virus (DENV) infection in mosquito midgut and dissemination in mosquitoes. We also show that mosquitoes express a plasmin-selective Kazal-type inhibitor (AaTI) in the midgut to inhibit plasmin proteolysis and revert the enhanced infection. Using bio-layer interferometry, we show that DENV, plasmin, and AaTI interact to form a tripartite complex. Eventually, plasmin increases midgut internalization of dextran molecules and this is reverted by AaTI. Our study demonstrates that (1) DENV recruits plasmin to increase local proteolytic activity in the midgut, thus degrading the glycocalyx and enhancing DENV internalization and (2) AaTI can act as a transmission-blocking agent by inhibiting plasmin proteolysis. Our results indicate that dengue pathogenesis enhances DENV fitness by increasing its infectivity to mosquitoes.