The RNA interference pathway modulates vector competence for Sindbis virus in the midgut of Aedes aegypti

Aedes aegypti mosquitoes are vectors of medically important arboviruses such as dengue and yellow fever viruses (Flaviviridae) and chikugunya virus (Togaviridae). After ingesting a viremic blood meal, arboviruses replicate in the mosquito midgut, a major organ that determines vector competence for arboviruses. In laboratory-reared Ae. aegypti, RNA interference (RNAi) has been shown to be an innate immune pathway that afects vector competence for dengue and Sindbis (Togaviridae) viruses. Here, we demonstrate that the mosquito midgut is an important organ where RNAi determines vector competence for Sindbis virus (SINV, strain TR339). We generated transgenic mosquitoes with down-regulation of the RNAi pathway gene, dicer2 in the midgut after a blood meal. Quantitative RT-PCR assay demonstrated that two out of five transgenic mosquito lines exhibited considerable reduction in dicer2 mRNA level after ingesting a blood meal. One of the lines, carb/dcr 16 was fed with infectious blood meal containing SINV. SINV titers in carb/dcr 16 midguts were higher compared to those in HWE control (non transgenic) mosquitoes. SINV dissemination from midguts to other tissues in carb/dcr 16 was also enhanced compared to that in HWE. The survival of carb/dcr 16 females was lower than that of HWE. We also showed variability in dicer2 mRNA levels among individual mosquitoes that might affect Ae. aegypti vector competence for SINV.