Inkoo and Sindbis viruses in blood sucking insects, and a serological study for Inkoo virus in semi-domesticated Eurasian tundra reindeer in Norway

Abstract

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, genus Alphavirus (Sindbis, Chikungunya), Flaviviridae (West Nile, Usutu, Dengue), and Peribunyaviridae, genus Orthobunyavirus, California serogroup (Inkoo, Batai, Tahyna). The principal focus of this study was Inkoo (INKV) and Sindbis (SINV) virus circulating in Norway, Sweden, Finland, and some parts of Russia. These viruses are associated with morbidity in humans. However, there is a knowledge gap regarding reservoirs and transmission. Therefore, we aimed to determine the prevalence of INKV and SINV in blood sucking insects and seroprevalence for INKV in semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus) in Norway. Materials and methods In total, 213 pools containing about 25 blood sucking insects (BSI) each and 480 reindeer sera were collected in eight Norwegian reindeer summer pasture districts during 2013–2015. The pools were analysed by RT-PCR to detect INKV and by RT-real-time PCR for SINV. Reindeer sera were analysed for INKV-specific IgG by an Indirect Immunofluorescence Assay (n = 480, IIFA) and a Plaque Reduction Neutralization Test (n = 60, PRNT). Results Aedes spp. were the most dominant species among the collected BSI. Two of the 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%. None of the analysed pools were positive for SINV. Overall IgG seroprevalence in reindeer was 62% positive for INKV by IIFA. Of the 60 reindeer sera- analysed by PRNT for INKV, 80% were confirmed positive, and there was no cross-reactivity with the closely related Tahyna virus (TAHV) and Snowshoe hare virus (SSHV). Conclusion The occurrence and prevalence of INKV in BSI and the high seroprevalence against the virus among semi-domesticated reindeer in Norway indicate that further studies are required for monitoring this virus. SINV was not detected in the BSI in this study, however, human cases of SINV infection are yearly reported from other regions such as Rjukan in south-central Norway. It is therefore essential to monitor both viruses in the human population. Our findings are important to raise awareness regarding the geographical distribution of these mosquito-borne viruses in Northern Europe.

Serological screening for tick‐borne encephalitis virus in eight Norwegian herds of semi‐domesticated reindeer (Rangifer tarandus tarandus)

“…Sequencing of RNA from reindeer nasal and/or rectal swabs have identified viral sequences representing the Flaviviridae family in reindeer in Norway, which is hosted mainly by arthropod vectors like ticks and mosquitoes (Romano et al, 2021). Furthermore, the mosquito‐borne virus INKV was detected in mosquitoes collected from Røros and INKV‐specific antibodies were detected in reindeer from all the reindeer herding areas included in this study (Shakya et al, 2022). In the present study, the TBE ELISA‐positive samples came from six out of eight locations from north to south of Norway where viable mosquito populations have been reported by Sánchez Romano et al (2021) and Shakya et al (2022) (Figure 1, Table 1).…”

“…Reindeer have been documented to support enzootic maintenance of viruses like herpesvirus, pestivirus and Hepatitis E virus (Rinaldo et al, 2021; Romano et al, 2021; Sacristán et al, 2021; Tryland et al, 2021). Recently, antibodies against Inkoo virus and Inkoo virus‐specific RNA were detected in reindeer for the first time in Norway which indicates that reindeer are exposed to a wide range of viruses (Shakya et al, 2022). The aim of the present study was to use semi‐domesticated reindeer from eight regions as sentinels to evaluate TBEV distribution from northern to southern Norway.…”

Mosquito-borne viruses causing human disease in Fennoscandia—Past, current, and future perspectives

“…The orthobunyaviruses found in Fennoscandia are Chatanga virus, Inkoo virus, Tahyna virus, and Batai virus. Of these four, all but Batai virus falls under the California serogroup, grouped together by their similarity to the prototypical California encephalitis virus (CEV) ( 21 , 22 ). The phylogeny of relevant viruses in the genus Orthobunyavirus is summarized in Figure 1 .…”

“…Seroprevalence in Norway has not been extensively studied in humans, though a 1985 survey of seroprevalence in Norwegian soldiers 22% of the recruits tested displayed antibodies to California serogroup viruses ( 53 ). High IgG seroprevalence has been reported in reindeer ( 22 ). Human disease caused by INKV is often asymptomatic, with evident disease characterized by an influenza-like illness.…”

“…These assays are not routinely used in clinical practice, except for in certain cases, eg. when certain notifiable diseases are suspected, as they are expensive and usually only available at some university hospitals ( 22 ). Some of these infections have well developed serological criteria, such as SINV, in which sensitivities of IgM and IgG enzyme immunoassays were reported as 97.6 and 100%; specificities were 95.2% and 97.6%, respectively ( 80 ).…”