Detection and genome analysis of a novel (dima)rhabdovirus (Riverside virus) from Ochlerotatus sp. mosquitoes in Central Europe

During an investigation for potential arboviruses present in mosquitoes in Hungary (Central Europe) three highly similar virus strains of a novel rhabdovirus (family Rhabdoviridae) called Riverside virus (RISV, KU248085-KU248087) were detected and genetically characterized from Ochlerotatus sp. mosquito pools collected from 3 geographical locations using viral metagenomic and RT-PCR methods. The ssRNA(−) genome of RISVs follows the general genome layout of rhabdoviruses (3′-N-P-M-G-L-5′) with two alternatives, small ORFs in the P and G genes (Px and Gx). The genome of RISVs contains some unusual features such as the large P proteins, the short M proteins with the absence of N-terminal region together with the undetectable “Late budding” motif and the overlap of P and M genes. The unusually long 3′ UTRs of the M genes of RISVs probably contain a remnant transcription termination signal which is suggesting the presence of an ancestral gene. The phylogenetic analysis and sequence comparisons show that the closest known relative of RISVs is the recently identified partially sequenced mosquito-borne rhabdovirus, North Creek virus (NOCRV), from Australia. The RISVs and NOCRV form a distinct, basally rooted lineage in the dimarhabdovirus supergroup. The host species range of RISVs is currently unknown, although the presence of these viruses especially in Ochlerotatus sp. mosquitoes which are known to be fierce biting pests of humans and warm-blooded animals and abundant and widespread in Hungary could hold some potential medical and/or veterinary risks.