Chikungunya virus resistant to the antiviral favipiravir is severely attenuated in mosquitoes

Abstract

It is currently unclear whether antiviral drug-resistant arboviruses can be transmitted by their mosquito vectors. We showed previously that the dissemination and the transmission of a chikungunya virus (CHIKV) resistant to the antiviral favipiravir was markedly decreased as compared to WT (Delang et al, mSphere 2018). The attenuated phenotype of this resistant virus was confirmed in Aag2 and C6/36 mosquito cells. Here, we aimed to study the mechanism of the attenuated phenotype in more detail. First, replication kinetics studies at 32°C for both Vero and mosquito cells confirmed that the attenuated fitness in mosquito cells is associated with the cell line and not with temperature. A passaging experiment of WT CHIKV on Vero cells in the absence of favipiravir showed that the observed attenuation of the resistant CHIKV was not due to passaging on Vero cells during the resistance selection. To identify the molecular mechanism of the attenuated phenotype, the genes encoding for the non-structural proteins (nsP) of the favipiravirres CHIKV were swapped into a WT CHIKV backbone. The replication fitness of these nsP2, nsP3 or nsP4 single swap variants did not differ significantly from the fitness of WT CHIKV in Vero and C6/36 cells, indicating that a combination of mutations in multiple non-structural proteins is responsible for the attenuated phenotype. Double nsP swap variants are therefore constructed and these will provide additional information on the molecular mechanism of the attenuation. Together, our results may provide interesting insights in the mosquito tropism of CHIKV.