RNA interference restricts Rift Valley fever virus in multiple insect systems

The emerging bunyavirus Rift Valley fever virus (RVFV) is transmitted to humans and livestock by a large number of mosquito species. RNA interference (RNAi) has been characterized as an important innate immune defense mechanism used by mosquitoes to limit replication of positive-sense RNA flavi- and togaviruses; however, little is known about its role against negative-strand RNA viruses such as RVFV. We show that virus-specific small RNAs are produced in infected mosquito cells, RVFV vector mosquitoes and those derived from the model insect Drosophila melanogaster. We also show that these have antiviral activity, since silencing of RNAi pathway effectors enhances viral replication. Moreover, our data suggest that RVFV does not encode for a suppressor of RNAi. These findings point towards a significant role of RNAi in the control of RVFV in mosquitoes.