EPIDEMIOLOGY OF SCHMALLENBERG VIRUS IN EUROPEAN BISON ( BISON BONASUS) IN POLAND.

Schmallenberg virus (SBV), an emerging arbovirus in Europe, is an important pathogen in domestic ruminants; however, its impact on free-ranging wild ruminants is not well studied. Three hundred and forty-seven serum samples collected between 2011 and 2016 from 302 European bison ( Bison bonasus) from 12 different sites in Poland were tested for the presence of SBV antibodies. In addition, 86 sera were collected between 2013 and 2016 from three species of cervids for testing for SBV antibodies. After the first detection of the virus in Poland in October 2012, the proportion of SBV-seropositive European bison reached 81% (95% confidence interval [CI]: 77.1-85.8%), whereas in cervids seroprevalence was 34% (95% CI: 23.5-43.9%). There was an increase in seroprevalence in European bison from 2012 to 2014. Biting midges ( Culicoides spp.), the primary vectors of SBV, were monitored entomologically for the identification of the biting midge populations and virologically for SBV infections in the Bialowieza Forest region, which contains the world's largest European bison population. We detected SBV by PCR in 3% of Culicoides pools from 2015. In addition, seven fetal brain samples from European bison or cervids were tested and were negative for SBV RNA. Our results indicate a high seroprevalence with reduced transmission of SBV in subsequent years in the European bison populations and lower seroprevalence in cervids.

Abundance and species composition of Culicoides spp. biting midges near cattle and horse in South-Eastern Poland.

The aim of the study was to estimate and compare the distribution of Culicoides biting midges species at farms with different main hosts - cattle and horse. Culicoides spp. are known vectors of arboviruses including African horse sickness virus (AHSV), bluetongue virus (BTV) and Schmallenberg virus (SBV). The latter two have been already reported in Polish ruminants recently, while AHSV remains absent, however the risk of its emergence has been increasing in the recent years. In order to establish the activity of potential AHSV vector at vicinity of horses, an OVI midge trap has been placed at the horse stables in the southeastern Poland. Another trap has been placed 7 km away at the cattle farm. The collections were carried over the midge activity season from April until November 2016. The midge abundances at both sites were comparable with the total numbers of insects trapped of 43,153 and 34,829 at the cattle and horse farm, respectively. Midges belonging to C. obsoletus/scoticus complex were the dominant ones at both locations. The other most abundant species were C. punctatus and C. pulicaris, while the other ten species identified (C. chiopterus, C. deltus, C. dewulfi, C. fagineus, C. impunctatus, C. newsteadi, C. nubeculosus, C. parroti, C. riethi, C. stigma) accounted for less than 0.5%. The study has shown that the Orbivirus vectors are present at a high abundance at the Polish horse farm, what may be a helpful tool in the AHS risk assessment in the nonendemic part of Europe.

Detection of the Schmallenberg virus in nulliparous Culicoides obsoletus/scoticus complex and C. punctatus--the possibility of transovarial virus transmission in the midge population and of a new vector.

The arthropod-borne Schmallenberg virus (SBV) emerged in Europe in the late summer/autumn of 2011. SBV spread across the continent until 2012. This paper presents SBV detection in female Culicoides spp. caught in UV traps located in 23 different locations in Poland. The midges were divided into pools containing 20.5 individual insects on average according to species and parity status. The study was based on duplex real-time reverse transcription PCR (RT-PCR) for the detection of the SBV S segment and culicoid 18S gene fragments. Forty-four out of 402 midge pools tested (10.9%) were found to be positive for the presence of viral RNA. The SBV positive Culicoides came from 10 traps spread randomly across the country and were collected between August and October 2012. The timing of the SBV positive midge collections and the locations of the traps corresponded to the epizootic situation of SBV in ruminants. SBV RNA was most frequently identified in gravid midges (36.4%), while in nulliparous, blood-fed and parous midges the percentages were 10.8% 13.0% and 8.1%, respectively. The majority (82%) of SBV positive pools belonged to Culicoides obsoletus/scoticus complex; however, viral RNA was also found in 8 out of the 149 (5.4%) Culicoides punctatus pools tested. While no statistical differences in the Ct values between different parity groups were found, the bimodal distribution observed at the Ct frequency plots suggested active SBV replication, especially in parous and gravid midge females, and sub-transmissible infection in nulliparous and blood-fed insects. The most important findings included identification of C. punctatus as a new possible vector of SBV and the recovery of viral RNA from the nulliparous females which may suggest transovarial transmission in C. obsoletus/scoticus complex and C. punctatus.