Exploring the role of the siRNA pathway in the vertical transmission of arboviruses by Aedes aegypti

Arthropod-borne viruses have been afflicting humans for millennia and continue to cause frequent epidemics by emergence and re-emergence events. Aedes aegypti, has been the vector causing all major epidemics. Arbovirus horizontal transmission (HT) between mosquitoes and humans is the main route of human infections, though vertical transmission (VT) from mosquito mother to her offspring is considered an evolutionary mechanism enabling viral persistence in nature during adverse periods for HT, and one of the likely explanations for virus reemergence. The biology of VT remains poorly studied and knowledge on molecular mechanisms, as well as host and viral factors driving VT of arboviruses is largely lacking. The small interfering RNA (siRNA) pathway is considered the most important and potent anti-viral defence system of mosquitoes. In this study, we investigated the role of the mosquito’s siRNA pathway in regulating VT of arboviruses by using transgenic Ae. aegypti with altered expression of key elements of this pathway: Dcr2 and Ago2. VT assays were performed with dengue virus type 2 and Mayaro virus. Viral dissemination to head and ovaries of exposed females was tested by plaque assay. Infection in progeny was also assessed by qPCR, and VT rates were estimates for each virus/mosquito strain combination. Comparison of dissemination rates in mothers and VT rates in progeny between transgenic and wild type mosquitoes provided information on the involvement the siRNA pathway in regulating the infection and VT of assayed arboviruses.