Pathogen-specific resistance to Rift Valley fever virus infection is induced in mosquito cells by expression of the recombinant nucleoprotein but not NSs non-structural protein sequences

Rift Valley fever virus (RVFV) is an arbovirus of the Bunyaviridae family, causing recurrent disease outbreaks in Africa. Natural vertebrate hosts include cattle and humans. Several mosquito species belonging to the Aedes and Culex genera act as vectors of this phlebovirus. To test whether pathogen-derived resistance against RVFV could be induced by expressing genomic sequences in mosquito cells, as has been shown for La Crosse and dengue 2 viruses, we generated various recombinant Semliki Forest viruses expressing the S segment (or its genes) in the genomic or antigenomic sense. Expression of the N but not the NSs gene interfered with the production of RVFV in mosquito cells and this phenomenon was RNA- but not protein-dependent. These results raise questions on the molecular mechanisms involved in virus resistance.