Post-epidemic Schmallenberg virus circulation: parallel bovine serological and Culicoides virological surveillance studies in Ireland

Abstract

BackgroundSchmallenberg virus (SBV) emerged in northern-Europe in 2011 resulting in an epidemic of ruminant abortions and congenital malformations throughout the continent. In the years following the epidemic there have been reports of SBV overwintering and continued circulation in several European countries. When the population-level of immunity declines in exposed regions, re-introduction of SBV could result in further outbreaks of Schmallenberg disease. The aims of this study were to determine the SBV seroprevalence in previously exposed Irish dairy herds in 2014 and to investigate if SBV continued to circulate in these herds in the three years (2013–2015) following the Irish Schmallenberg epidemic.Whole-herd SBV serosurveillance was conducted in 26 herds before (spring) and following the 2014 vector-season (winter), and following the 2015 vector-season (winter). In spring 2014, 5,531 blood samples were collected from 4,070 cows and 1,461 heifers. In winter 2014, 2,483 blood samples were collected from 1,550 youngstock (8–10 months old) and a subsample (n = 933; 288 cows, 645 heifers) of the seronegative animals identified in the spring. Youngstock were resampled in winter 2015. Culicoides spp. were collected in 10 herds during the 2014 vector-season and analysed for SBV; a total of 138 pools (3,048 Culicoides) from 6 SBV vector species were tested for SBV RNA using real-time PCR.ResultsIn spring 2014, animal-level seroprevalence was 62.5 % (cows = 84.7 %; heifers = 0.6 %). Within-herd seroprevalence ranged widely from 8.5 %–84.1 % in the 26 herds. In winter 2014, 22 animals (0.9 %; 10 cows, 5 heifers, 7 youngstock) originating in 17 herds (range 1–4 animals/herd) tested seropositive. In winter 2015 all youngstock, including the 7 seropositive animals in winter 2014, tested seronegative suggesting their initial positive result was due to persistence of maternal antibodies. All of the Culicoides pools examined tested negative for SBV-RNA.ConclusionsSBV appears to have recirculated at a very low level in these herds during 2013 and 2014, while there was no evidence of SBV infection in naïve youngstock during 2015. A large population of naïve animals was identified and may be at risk of infection in future years should SBV re-emerge and recirculate as it has done in continental Europe.

Evidence of extensive renewed Schmallenberg virus circulation in Belgium during summer of 2016 - increase in arthrogryposis-hydranencephaly cases expected

“…This is clearly lower than the previously reported overall seroprevalence and between‐herd seroprevalence of, respectively, 65% and 100% reported at the end of the vector season of 2012 (Méroc, Poskin, Van Loo, Van Driessche et al., ). This seems to be in line with the general assumption that the SBV circulation in Belgium and other European countries has ceased since 2012, leading to a decline in the proportion of sheep that have been into contact with the virus and harbor SBV‐specific antibodies (Collins, Barrett, Doherty, Larska, & Mee, ; Gache et al., ; Poskin et al., ; Stokes, Baylis, & Duncan, ; Wernike, Holsteg, Sasserath, & Beer, ).…”

A survey of free-ranging deer in Ireland for serological evidence of exposure to bovine viral diarrhoea virus, bovine herpes virus-1, bluetongue virus and Schmallenberg virus

“…In Belgium, a seroprevalence of 43.1% was reported in red and roe deer sampled in Wallonia in the autumn of 2011 [63], while in Flanders a 63% seroprevalence was reported in roe deer sampled in 2012 [54]. These higher seroprevalence levels relative to those reported in the current study may reflect differences between studies in the timing of sampling relative to the emergence of SBV, the failure of SBV to become established in Ireland [61] or underlying ecological or epidemiological differences.…”

“…However, the presence of suitable BTV vector species in Ireland [6, 61] indicates that the virus could become established if introduced and highlights the need for continued surveillance.…”

Significant re-emergence and recirculation of Schmallenberg virus in previously exposed dairy herds in Ireland in 2016

“…In the years following the European Schmallenberg epidemic (2014–2016), there have been reports of SBV overwintering and continued virus circulation in a number of European countries (Bayrou, Garigliany, Cassart, Sartelet, & Desmecht, ; Elbers, Meiswinkel, van Weezep, Kooi, & van der Poel, ; Gache et al., ; Meroc et al., ; Wernike, Hoffmann, Conraths, & Beer, ), including Ireland (Collins, Barrett, Doherty, Larska, & Mee, ), albeit at a considerably lower level when compared to the level of SBV circulation during the first European epidemic. The lack of significant virus recirculation in the last number of years has resulted in a growing population of immunologically naïve animals (Collins et al., ; Poskin et al., ; Veldhuis, Mars, Roos, van Wuyckhuise, & van Schaik, ) which would be susceptible to SBV infection should the virus re‐emerge in previously exposed and unexposed regions. In 2016, Collins et al.…”

“…In 2016, Collins et al. () hypothesized that SBV would follow a similar cyclical epidemiological pattern of circulation to Akabane disease epidemics, where SBV would re‐emerge in previously exposed regions as the herd‐level of immunity declines and in turn result in a new epidemic of Schmallenberg disease.…”