Inkoo And Sindbis Viruses In Semi-Domesticated Reindeer And Mosquitoes In Norway

Background: Mosquito-borne viruses pose a serious threat to humans worldwide. There has been an upsurge in the number of mosquito-borne viruses in Europe, mostly belonging to the families Togaviridae (Sindbis, Chikungunya), Flaviviridae (West Nile, Usutu, Dengue), and Peribunyaviridae (Inkoo, Batai, Tahyna). The principal focus of this study was Inkoo (INKV) and Sindbis (SINV) virus circulating in Norway because there is a knowledge gap regarding reservoirs and transmission. Therefore, we aimed to determine the prevalence of SINV and INKV in mosquitoes and seroprevalence of INKV in semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus).Methods: In total, 213 pools containing about 25 mosquitoes each and 480 reindeer sera were collected in eight Norwegian reindeer summer pasture districts during 2013-2015. The mosquito pools were analysed for INKV and SINV RNA, with reverse transcriptase (RT)-real time quantitative PCR (RT-qPCR), and pyrosequencing. Reindeer sera were analysed for INKV-specific IgG by Indirect Immunofluorescence Assay (IIFA) and Plaque Reduction Neutralization Test (PRNT).Results: Aedes spp. were the most dominant species among the collected mosquitoes. Two of the mosquito pools were positive for INKV-RNA by RT-PCR and were confirmed by pyrosequencing. The overall estimated pool prevalence (EPP) of INKV in Norway was 0.04%. IgG seroprevalence in reindeer revealed 60% positive for INKV by IIFA. Of the 55 borderline reindeer sera, 24% were positive on cytopathic effect (CPE)-neutralization test. Among 80% of 60 reindeer sera analysed with PRNT for INKV had a titre ≥ 20, and there was no cross-reactivity with the closely related Tahyna virus (TAHV) and Snow Shoe Hare virus (SSHV). None of the analysed mosquito pools were positive for SINV.Conclusions: The occurrence and prevalence of INKV in Aedes mosquitoes and its high seroprevalence among semi-domesticated reindeer in Norway indicate that further studies are required for monitoring this virus. SINV was not detected in the mosquitoes in this study, however, human cases of SINV infection have yearly been reported from Rjukan. Therefore, it is essential to investigate SINV among human population. Our findings are important to raise awareness regarding the geographical distribution of these mosquito-borne viruses in Northern Europe.