Mechanisms and Genetic Determinants of Alphavirus Infection of Mosquito Vectors

Venezuelan equine encephalitis virus (VEEV) is a mosquito-borne disease that has caused hundreds-of-thousands of human and equine cases. Since epizootic strains have historically been the largest public health threat, the majority of experimental studies have focused on these strains. Recently, there has been an increase in the number of cases caused by enzootic strains, IE and ID, which illustrates the importance of understanding how these viruses interact with their mosquito vector. Studies examining the interaction between epizootic strains and their vector indicate that the primary viral determinants for successful infection of epizootic mosquito vector can be mapped to the E2 glycoprotein region. I hypothesized that in addition to the E2 glycoprotein, regions outside of the E2 glycoprotein determine successful infection by enzootic strains of their mosquito vector, Culex taeniopus and examined this hypothesis utilizing chimeric viruses of epizootic IAB and enzootic IE VEEV strains. My findings support my hypothesis that the regions of the E2 glycoprotein are not solely responsible for enzootic vector infection and suggest that the 3’ UTR might also be a determinant of enzootic vector infection. The second focus of this dissertation was to examine the particular characteristics of initial midgut infection and dissemination by IE VEEV in Cx. taeniopus. Given previous findings suggesting that the epizootic mosquito vector has a limited number of susceptible midgut cells, I hypothesized that the enzootic vector would not have a restricted population of susceptible midgut cells and orally infected Cx. taeniopus mosquitoes with replicon particles to examine this hypothesis. My findings suggest that there is not a restricted population of susceptible midgut epithelial cells and enzootic IE virions do not have a predilection for infection of a particular region of the posterior midgut epithelium. I additionally proposed to elucidate the route of enzootic viral escape from the Cx. taeniopus midgut and hypothesized that the virions utilized the mosquito tracheal system to bypass the basal lamina associated with the midgut. I utilized a IE virus encoding a green fluorescent protein (GFP), but was unable to determine the route of dissemination due to attenuation of the virus as a result of the GFP inclusion.