Infection and Transmission of Rift Valley Fever Viruses Lacking the NSs and/or NSm Genes in Mosquitoes: Potential Role for NSm in Mosquito Infection

Abstract

BackgroundRift Valley fever virus is an arthropod-borne human and animal pathogen responsible for large outbreaks of acute and febrile illness throughout Africa and the Arabian Peninsula. Reverse genetics technology has been used to develop deletion mutants of the virus that lack the NSs and/or NSm virulence genes and have been shown to be stable, immunogenic and protective against Rift Valley fever virus infection in animals. We assessed the potential for these deletion mutant viruses to infect and be transmitted by Aedes mosquitoes, which are the principal vectors for maintenance of the virus in nature and emergence of virus initiating disease outbreaks, and by Culex mosquitoes which are important amplification vectors.Methodology and Principal Findings Aedes aegypti and Culex quinquefasciatus mosquitoes were fed bloodmeals containing the deletion mutant viruses. Two weeks post-exposure mosquitoes were assayed for infection, dissemination, and transmission. In Ae. aegypti, infection and transmission rates of the NSs deletion virus were similar to wild type virus while dissemination rates were significantly reduced. Infection and dissemination rates for the NSm deletion virus were lower compared to wild type. Virus lacking both NSs and NSm failed to infect Ae. aegypti. In Cx. quinquefasciatus, infection rates for viruses lacking NSm or both NSs and NSm were lower than for wild type virus.Conclusions/SignificanceIn both species, deletion of NSm or both NSs and NSm reduced the infection and transmission potential of the virus. Deletion of both NSs and NSm resulted in the highest level of attenuation of virus replication. Deletion of NSm alone was sufficient to nearly abolish infection in Aedes aegypti mosquitoes, indicating an important role for this protein. The double deleted viruses represent an ideal vaccine profile in terms of environmental containment due to lack of ability to efficiently infect and be transmitted by mosquitoes.

Rift Valley fever virus: strategies for maintenance, survival and vertical transmission in mosquitoes

“…Inability to enter or replicate in the midgut epithelium is termed the midgut infection barrier. Delay or prevention of dissemination is collectively termed the midgut escape barrier and is dose-dependent [71][72][73] interference (RNAi) (reviewed in [75]), virus inactivation by digestive enzymes and virus incompatibility with host receptors, for example deleting NSm in RVFV impedes infection in Aedes aegypti [67,76,77]. Once in the haemocoel, virus is actively circulated in the haemolymph to all tissues including the salivary glands and ovaries.…”

Dicer-2- and Piwi-Mediated RNA Interference in Rift Valley Fever Virus-Infected Mosquito Cells

“…In contrast to the case with vertebrates, very little is known about the effect of RVFV infection in mosquitoes and the response to RVFV infection developed by these arthropods (47,48). In this work, we analyzed infection in three mosquito cell lines originating with Aedes aegypti (Aag2) and A. albopictus (U4.4 and C6/36).…”

Nuclear Relocalization of Polyadenylate Binding Protein during Rift Valley Fever Virus Infection Involves Expression of the NSs Gene

“…While NSm is dispensable for replication in cell culture and animal models, it has been shown to inhibit apoptosis in infected cells (15)(16)(17)(18). Additionally, NSm has been shown to be important for RVFV infection and transmission in mosquitoes (19). The S segment encodes the nucleocapsid protein (N) in negative sense and a nonstructural protein, NSs, in positive sense (20).…”