Genetic Determinants of Differential Oral Infection Phenotypes of West Nile and St. Louis Encephalitis Viruses in Culex spp. Mosquitoes.

Maharaj PD1, Bolling BG1, Anishchenko M1, Reisen WK1, Brault AC2.

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Abstract

St. Louis encephalitis virus (SLEV) has shown greater susceptibility to oral infectivity than West Nile virus (WNV) in Culex mosquitoes. To identify the viral genetic elements that modulate these disparate phenotypes, structural chimeras (WNV-pre-membrane [prM] and envelope [E] proteins [prME]/SLEV.IC and SLEV-prME/WNV.IC) were constructed in which two of the structural proteins, the prM and E, were interchanged between viruses. Oral dose-response assessment with the chimeric/parental WNV and SLEV was performed to characterize the infection phenotypes in Culex mosquitoes by artificial oral blood meals. The median infectious dose required to infect 50% of Cx. quinquefasciatus with WNV was indistinguishable from that of the SLEV-prME/WNV.IC chimeric virus. Similarly, SLEV and WNV-prME/SLEV.IC virus exhibited an indistinguishable oral dose-response relationship in Cx. quinquefasciatus. Infection rates for WNV.IC and SLEV-prME/WNV.IC were significantly lower than SLEV.IC and WNV-prME/SLEV.IC infection rates. These results indicated that WNV and SLEV oral infectivities are not mediated by genetic differences within the prM and E proteins.