Schmallenberg virus: State of Art

Failure to detect Schmallenberg virus RNA in ram semen in the UK (2016-2018)

Background

Schmallenberg virus (SBV) is a midge-borne arbovirus that first emerged in the European ruminant population in 2011 and has since settled to an endemic pattern of disease outbreaks on an approximately 4-year cycle when herd immunity from the previous circulation drops to a point allowing renewed widescale virus circulation. The impacts of trade restrictions on genetic products (semen, embryos) from affected areas were severe, particularly after the discovery that the virus is intermittently shed in the semen of a small number of bulls. The trade in small ruminant (ram and goat) semen is less than that of bulls; nonetheless, there has been no study into the shedding rate of SBV in ram semen.

Methods

Semen samples (n = 65) were collected as part of UK ram trials and artificial insemination studies around the period of the 2016-2018 SBV recirculation. Semen was preserved in RNAlater for shipping, and RNA extraction with RNeasy and S gene RT-quantitative PCR performed for SBV nucleic acid detection.

Results

No SBV RNA was detected in any samples.

Conclusions

While larger numbers of animals would be needed to completely exclude the possibility of SBV shedding in ram semen, this trial nonetheless highlights that this is likely a rare event if it occurs at all and is unlikely to play a role in disease transmission.

Survey of Culicoides-borne Bluetongue and Schmallenberg viruses at the wildlife-livestock interface in Doñana National Park (Spain)

A cross-sectional study was carried out to assess the circulation of bluetongue virus (BTV) and Schmallenberg virus (SBV) within the wild and domestic ungulate host community in Doñana National Park (southwestern Spain). A total of 440 animals, including 138 cattle, 102 red deer (Cervus elaphus), 101 fallow deer (Dama dama) and 99 wild boar (Sus scrofa) were sampled in 2015 during the seasonal peak of Culicoides spp. (summer-autumn). Serum and spleen samples were analysed to detect exposure (using commercial blocking ELISAs) and infection (by RT-PCR), respectively, to BTV and SBV. Cattle were not tested by BTV-bELISA because all were previously vaccinated against BTV serotypes 1 and 4. High BTV seroprevalences were found in red deer (97.0%) and fallow deer (64.7%). Antibodies against SBV were detected in 37.0% of cattle, 16.8% of red deer, 23.5% of fallow deer and 2.0% of wild boar. Thirty-eight of the 203 deer (18.7%; 17 red deer and 21 fallow deer) were co-exposed to both viral agents. BTV-4 RNA was confirmed in four red deer and two fallow deer. SBV RNA was found in two fallow deer. Co-infections were not detected. Our results indicate high exposure, widespread distribution, and active circulation of BTV and SBV in the ruminant community in the study area. We provide additional evidence for the potential role of wild cervids as reservoirs of these Culicoides-borne viruses in two different epidemiological scenarios: with vaccination (BTV) and without vaccination (SBV) of sympatric livestock. This study highlights the importance of wildlife surveillance, particularly of cervid species, for the proper execution of control programmes of Culicoides-borne diseases in extensively reared livestock. This article is protected by copyright. All rights reserved.

Schmallenberg virus in Poland endemic or re-emerging? A six-year serosurvey

A novel arbovirus, called Schmallenberg virus (SBV), emerged in Europe in 2011 infecting domestic as well as wild ruminants. The virus was first detected in Poland during the 2012 vector season. In order to study the SBV post-epidemic period in Poland, over twenty-one thousand domestic ruminants (cattle, sheep, goats) were tested for SBV infection between 2013 and 2018. Samples were collected as part of the national Bluetongue virus (BTV) surveillance programme. Thirteen per cent of all samples were collected from animals between 6 months and one year of age. Overall, 37.5% of ruminants tested seropositive. The seroprevalence fluctuated yearly and was highest in 2014 and 2017; however, seroconversion was detected in younger animals throughout the study indicating continuous virus circulation during the 6-year study period. A significantly higher proportion of seropositive animals were detected among cattle and older animals. Uneven distribution of seropositive animals between provinces was identified and may be a result of different housing and breeding practices and/or meteorological conditions influencing local and regional vector abundances, rather than farm stocking densities. A small number of animals were identified as being exposed to both SBV and BTV; this is likely due to the fact that the same Culicoides species transmit these two viruses thus increasing the risk of co-exposure. Considering these results, in addition to virological and entomological studies carried out in Poland previously, it can be concluded that SBV is endemic in Poland with cyclical waves of virus circulation happening every 3-4 years.

Serosurveillance of Schmallenberg virus in wild ruminants in Spain

Schmallenberg disease (SBD) is an emerging vector-borne disease that affects domestic and wild ruminants. A long-term serosurvey was conducted to assess exposure to Schmallenberg virus (SBV) in all the wild ruminant species present in mainland Spain. Between 2010 and 2016, sera from 1,216 animals were tested for antibodies against SBV using a commercial blocking ELISA. The overall prevalence of antibodies was 27.1% (95%CI: 24.7-29.7). Statistically significant differences among species were observed, with significantly higher seropositivity found in fallow deer (Dama dama) (45.6%; 99/217), red deer (Cervus elaphus) (31.6%; 97/307) and mouflon (Ovis aries musimon) (28.0%; 33/118) compared to Barbary sheep (Ammotragus lervia) (22.2%; 8/36), Iberian wild goat (Capra pyrenaica) (19.9%; 49/246), roe deer (Capreolus capreolus) (17.5%; 34/194) and Southern chamois (Rupicapra pyrenaica) (10.2%; 10/98). Seropositive animals were detected in 81.4% (57/70; 95%CI: 70.8-88.8) of the sampled populations. SBV seroprevalence ranged from 18.8% (48/256) in bioregion (BR)2 (north-central, Mediterranean) to 32.3% (31/96) in BR1 (northeastern or Atlantic, Eurosiberian). Anti-SBV antibodies were not found before 2012, when the first outbreak of SBD was reported in Spain. In contrast, seropositivity was detected uninterruptedly during the period 2012-2016 and anti-SBV antibodies were found in yearling animals in each of these years. Our results provide evidence of widespread endemic circulation of SBV among wild ruminant populations in mainland Spain in recent years. Surveillance in these species could be a useful tool for monitoring SBV in Europe, particularly in areas where wild ruminants share habitats with livestock.

Cross-sectional study of British wild deer for evidence of Schmallenberg virus infection

BACKGROUND

Schmallenberg virus (SBV) is an orthobunyavirus, carried by Culicoides biting midges, that causes reproductive problems in adult ruminants when infected during their gestation period. SBV was first detected in ruminants in the UK in 2011/2012 and then again in 2016. The reason behind the 2016 re-emergence of SBV is unknown, but one possibility is that it can be maintained in wildlife, such as deer. SBV has been detected at high seroprevalence in deer in a number of European countries, but only once in the UK in a single region.

METHODS

The purpose of this study was to survey wild deer across Great Britain for recent evidence of SBV. Deer hunters were recruited for the purpose of providing postmortem blood samples to be tested for SBV antibodies.

RESULTS

The seroprevalence of SBV in the British wild deer population was 13.8 per cent; found in red, roe, muntjac and fallow deer species, with more in deer further south.

CONCLUSION

These results support the growing concern that SBV is now endemic in Great Britain and highlight the need to know the role of wildlife in SBV transmission.

Post-epidemic investigation of Schmallenberg virus in wild ruminants in Slovenia

Schmallenberg virus (SBV) is a vector-borne virus belonging to the genus Orthobunyavirus within the Bunyaviridae family. SBV emerged in Europe in 2011 and was characterized by epidemics of abortions, stillbirths and congenital malformations in domestic ruminants. The first evidence of SBV infection in Slovenia was from an ELISA-positive sample from a cow collected in August 2012; clinical manifestations of SBV disease in sheep and cattle were observed in 2013, with SBV RNA detected in samples collected from a total of 28 herds. A potential re-emergence of SBV in Europe is predicted to occur when population-level immunity declines. SBV is also capable of infecting several wild ruminant species, although clinical disease has not yet been described in these species. Data on SBV-positive wild ruminants suggest that these species might be possible sources for the re-emergence of SBV. The aim of this study was to investigate whether SBV was circulating among wild ruminants in Slovenia and whether these species can act as a virus reservoir. A total of 281 blood and spleen samples from wild ruminants, including roe deer, red deer, chamois and European mouflon, were collected during the 2017-2018 hunting season. Serum samples were tested for antibodies against SBV by ELISA; the overall seroprevalence was 18.1%. Seropositive samples were reported from all over the country in examined animal species from 1 to 15 years of age. Spleen samples from the seropositive animals and serum samples from the seronegative animals were tested for the presence of SBV RNA using real-time RT-PCR; all the samples tested negative. Based on the results of the seropositive animals, it was demonstrated that SBV was circulating in wild ruminant populations in Slovenia even after the epidemic, as almost half (23/51) of the seropositive animals were 1 or 2 years old.

Seroprevalence of bovine arboviruses belonging to genus Orthobunyavirus in South Korea

Arboviruses, belonging to the Simbu serogroup of the genus Orthobunyavirus, often cause congenital malformations and reproductive loss in cattle. The recent occurrences of such reproductive problems suggest that new arboviruses have emerged in Japan. However, there is no information on the presence of these viruses in South Korea. The aim of this study was to determine the presence of antibodies for Akabane, Aino, Peaton, Sathuperi, and Shamonda viruses in four regions, namely Gyeonggi, Jeollabuk, Jeollanam provinces, and Jeju Island of South Korea by a serum neutralization test. Antibody positivity against Akabane, Aino, Peaton, Sathuperi, and Shamonda viruses was detected in the country, with average seropositive rates of 10.4, 4.5, 1.1, 4.9, and 5.6%, respectively.

Epizootiological study on spatiotemporal clusters of Schmallenberg virus and Lumpy skin diseases: The case of Russia

Aim:

The submitted article attempts to highlight and specify the development of Schmallenberg virus (SBV) and lumpy skin disease (LSD) in cartographic illustrations, as well as to assess the epizootic situation of these diseases in the world, especially in Russia.

Materials and Methods:

Outbreaks (samples were collected from clinically healthy as well as suspected animals in infected areas) were confirmed and reported to the World Organization for Animal Health by veterinary officials representing countries in different geographical regions in the world. The reports showed that ELISA and polymerase chain reaction were used to identify SBV and LSD, taking into account number of infected, dead, and susceptible animals in infection foci since their first registration including in Russia. Once conventional statistical population (arrange data according to the main goal by regions, infected, and dead animals) was defined, a model was installed. A geo-information system, QuickMAP, was used to clarify the disease distribution map, and through the illustrations, analysis values were obtained.

Results:

Using information clusters of some epizootological criteria in various territories has demonstrated 1.302 focus of infection of SBV, of which 63.22% were registered in Europe and 36.78% in Russia. The seroprevalence in Russia was about 7.92% of the examined animals. According to the morbidity structure, the causative agent mainly affected cattle (64.76%), small ruminants (33.68%), and goats (1.56%). A global assessment of the effectiveness of primary epizootic diagnosis by practicing veterinarians was 63.19%, i.e., of 100 suspicion reports of SBV, 63.19 cases are confirmed by laboratory methods. A detailed assessment of the types of animals affected by the disease showed that it was easily diagnosed in sheep (70.38%), cattle (60.4%), and goats (48.57%), respectively. In the wild animal species, a significant prevalence was recorded as- 54.5%. In 2016, 1.209 foci of LSD were registered in the world, with 20.548 heads of cattle affected, while 8.5% of them identified in Russia (in 2017, the figure was 7.5%). Different maps had been generated in QuickMAP. Cluster analysis of the infected livestock in different regions in Russia showed that, in 2016, the Chechen Republic, Krasnodar, and Volgograd regions were, respectively, severely, moderately, and mildly affected. In 2017, the situation changed and Saratov, Orenburg regions, and Bashkiria were severely affected. However, the number of outbreaks decreased by 84.81% by contribution to the previous year. Eritrea, Namibia, and South Africa were leading in a cluster of most infected areas in 2017.

Conclusion:

Infectious diseases do not know borders. The emergence of SBV and LSD in the territory of the Russian Federation has followed the most common general dynamics of transborder diseases without ignoring details. The epizootic risk from wild animals and favorable climatic conditions is critical to fight against transmission of these diseases in Russia.

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 Białowieża 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.

Activity of Culicoides spp. (Diptera: Ceratopogonidae) inside and outside of livestock stables in late winter and spring

Culicoides Latreille, 1809 midge species are the putative vectors of Bluetongue virus (BTV) and Schmallenberg virus (SBV) in Europe. To gain a better understanding of the epidemiology of the diseases, basic knowledge about the overwintering of the vectors is needed. Therefore, we investigated culicoid activity in relation to air temperature at livestock stables during late winter and spring season. Ceratopogonids were captured weekly indoors and outdoors on three cattle farms, three horse farms and one sheep farm in the federal state of Brandenburg, Germany between January and May, 2015 by BG-Sentinel UV-light suction traps. First seasonal activity was measured inside a sheep barn and cattle stables in mid-March, suggesting the existence of a preceding vector-free period. The first species at all trapping sites were members of the Obsoletus Complex followed by Culicoides punctatus (Meigen), 1804 and Culicoides pulicaris (Linnaeus), 1758 simultaneously. In total, 160 collections were made, including 3465 Culicoides specimens with 2790 (80.6%) of them being members of the Obsoletus Complex. The remaining 675 individuals belonged to six other culicoid species. 59.8% of all Culicoides were collected indoors, and almost five times as many midges were sampled on cattle farms as on horse farms. Cattle farms harboured seven species while only two species were found on the horse and the sheep farms, respectively. Temperatures, husbandry practises and the presence/quality of potential breeding sites might be responsible for the difference in species and numbers of caught specimens between livestock holdings.

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

Background

Schmallenberg 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.

Results

In 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.

Conclusions

SBV 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.

Application of integrated production and economic models to estimate the impact of Schmallenberg virus for various sheep production types in the UK and France

Objective

The present study aimed to estimate and compare the economic impact of Schmallenberg virus (SBV) in different sheep production holdings using partial budget and gross margin analyses in combination with production models.

Participants

The sheep production types considered were lowland spring lambing, upland spring lambing and early lambing flocks in the UK, and grass lamb flocks of the Centre and West of France, extensive lambing flocks and dairy sheep flocks in France.

Methodology

Two disease scenarios with distinct input parameters associated with reproductive problems were considered: low and high impact. Sensitivity analyses were performed for the most uncertain input parameters, and the models were run with all of the lowest and highest values to estimate the range of disease impact.

Results

The estimated net SBV disease cost per year and ewe for the UK was £19.65–£20.85 for the high impact scenario and £6.40–£6.58 for the low impact scenario. No major differences were observed between the different production types. For France, the net SBV disease cost per year and ewe for the meat sheep holdings was £15.59–£17.20 for the high impact scenario and £4.75–£5.26 for the low impact scenario. For the dairy sheep, the costs per year and ewe were £29.81 for the high impact scenario and £10.34 for the low impact scenario.

Conclusions

The models represent a useful decision support tool for farmers and veterinarians who are facing decisions regarding disease control measures. They allow estimating disease impact on a farm accounting for differing production practices, which creates the necessary basis for cost effectiveness analysis of intervention strategies, such as vaccination.