Nonvascular delivery of St. Louis encephalitis and Venezuelan equine encephalitis viruses by infected mosquitoes (Diptera: Culicidae) feeding on a vertebrate host.

We determined whether mosquitoes infected with the viruses St. Louis encephalitis (SLE) or Venezuelan equine encephalitis inoculate virus extravascularly or directly into the vascular system. Infected mosquitoes fed on the distal 3rd of the tails of suckling mice. Significantly more mice whose tails were amputated at the midpoint within 10 min of mosquito feeding survived than did siblings whose tails remained intact. Even when tails were amputated 1-6 h after SLE virus-infected mosquitoes fed, the median time to death was significantly longer in mice with amputated tails (7.1 d) than in mice with intact tails (5.8 d). We concluded that mosquitoes inoculated virus primarily extravascularly, rather than directly into the vascular system, while feeding on a vertebrate host. Extravascular, rather than intravascular, delivery of pathogens by mosquitoes may affect disease pathogenesis and vaccine efficacy.