Survey of Schmallenberg virus (SBV) infection in German goat flocks

Exposure of small ruminants to the Schmallenberg arbovirus in Germany from 2017 to 2018 - animal-specific and flock-management-related risk factors

The Schmallenberg virus (SBV), an emerging Orthobunyavirus of mainly ruminant hosts, caused a substantial epidemic in European ruminant populations between 2011 and 2013. The pathogen is transmitted by arthropod vectors (Culicoides spp.) and can cause reproductive disorders and severe malformations of the offspring or stillbirth. The present study aimed to assess SBV seroprevalence among German sheep and goats a few years after the first virus detection in the country (November 2011). In addition, an extensive risk factor analysis including host-specific and husbandry-related factors was implemented. Seroprevalence was determined by examining serum samples from 2759 sheep and 446 goats out of a total of 70 flocks across five German federal states. The samples were withdrawn in the period between 2017 and 2018. Using a commercial competitive ELISA, antibodies against SBV were detected in all 70 investigated flocks. A percentage of 60.1 % (1657/2759) of the sheep and 40.4 % (180/446) of the goat sera contained SBV antibodies. Generalized linear mixed modeling revealed significant effects of host species (sheep > goats), age (old > young) and sex (female > male) on SBV seroprevalence. For both species, also the farming purpose, and for goats, ectoparasite treatment and the presence of cattle on the farm played a role in terms of risk for SBV exposure. The observations from this study still emphasize a wide distribution of the pathogen in Germany. Nevertheless, the observed seroprevalence might not be sufficient to achieve effective herd immunity. Pinpointing risk factors identified susceptible populations for targeted vaccination programs to reduce potential animal losses caused by SBV.

An outbreak of Akabane disease in a cattle herd on the Mughan plain, Iran

In November 2021, an investigation was conducted into an outbreak of abortion, stillbirth, and the birth of calves with congenital abnormalities (arthrogryposis and hydranencephaly) at a dairy farm in Dasht-e-Mughan city, Ardabil province. A total of 70 cows experienced these issues. To determine the cause of the outbreak, post-mortem brain tissue samples were collected from two calves affected by hydranencephaly, which occurred shortly after their birth. Polymerase chain reaction (PCR) testing was conducted for multiple viruses, including bovine viral diarrhea (BVD), border disease, Akabane, Schmallenberg, and bluetongue viruses (BTVs). The samples were positive only for Akabane virus. Serum samples were collected from a group of 60 cattle, consisting of 45 adult cows and 15 younger calves aged between 8 to 10 months. These samples were analyzed to detect the presence of antibodies against the Akabane and Schmallenberg viruses. Both of these viruses are known to be responsible for causing abortion, stillbirth, and congenital abnormalities in calves. Among 45 cows that tested by competitive enzyme-linked immunosorbent assay (cELISA), 26.66% and 33.33% exhibited antibodies against Akabane and Schmallenberg viruses, respectively. Notably, 20.00% of cows co-exhibited antibodies for both viruses. Despite PCR evidence implicating Akabane virus as the principal etiology of clinical signs observed in the affected herd, the high co-seropositivity to Schmallenberg virus, warrants a thorough investigation into potential viral interactions. Further research is required to determine the source of the virus and their transmission routes. This information could facilitate the refinement of disease control strategies and improving the management of reproductive challenges in such affected herds.

Schmallenberg virus, cyclical reemergence in the core region: A seroepidemiologic study in wild cervids, Belgium, 2012-2017

Schmallenberg virus emerged in 2011 in Europe. The epicentre of primordial spreading was the region straddling Germany, the Netherlands and Belgium. One of the key questions is whether the newcomer would establish a lasting presence on the continent. The apparent seroprevalence in southern Belgium wild deer populations was followed for 6 years. Two years of intense circulation were revealed, 2012 and 2016, characterized by a peak seroprevalence in the two studied populations (Capreolus capreolus and Cervus elaphus). Between the peak years and after 2016, apparent seroprevalences declined rapidly among adults and became nil among juveniles. The general pattern of apparent seroprevalence evolution observed is consistent with a cyclic circulation of Schmallenberg virus, similar to what is observed for other Orthobunyaviruses in endemic areas. These data also suggest that wild cervids play no central role in the circulation dynamics of the virus.

Schmallenberg Virus: To Vaccinate, or Not to Vaccinate?

Schmallenberg virus (SBV), a teratogenic orthobunyavirus that infects predominantly ruminants, emerged in 2011 in Central Europe, spread rapidly throughout the continent, and subsequently established an endemic status with re-circulations to a larger extent every 2 to 3 years. Hence, it represents a constant threat to the continent's ruminant population when no effective countermeasures are implemented. Here, we discuss potential preventive measures to protect from Schmallenberg disease. Previous experiences with other arboviruses like bluetongue virus have already demonstrated that vaccination of livestock against a vector-transmitted disease can play a major role in reducing or even stopping virus circulation. For SBV, specific inactivated whole-virus vaccines have been developed and marketing authorizations were granted for such preparations. In addition, candidate marker vaccines either as live attenuated, DNA-mediated, subunit or live-vectored preparations have been developed, but none of these DIVA-capable candidate vaccines are currently commercially available. At the moment, the licensed inactivated vaccines are used only to a very limited extent. The high seroprevalence rates induced in years of virus re-occurrence to a larger extent, the wave-like and sometimes hard to predict circulation pattern of SBV, and the expenditures of time and costs for the vaccinations presumably impact on the willingness to vaccinate. However, one should bear in mind that the consequence of seronegative young animals and regular renewed virus circulation might be again more cases of fetal malformation caused by an infection of naïve dams during one of their first gestations. Therefore, an appropriate and cost-effective strategy might be to vaccinate naïve female animals of all affected species before the reproductive age.

Schmallenberg Disease-A Newly Emerged Culicoides-borne Viral Disease of Ruminants

First appearing in 2011 in Northern Europe, Schmallenberg virus (SBV), an Orthobunyavirus of the Simbu serogroup, is associated with clinical disease mainly in ruminants such as cattle, sheep and goats. The clinical signs are characterized by abortion and congenital deformities in newborns. The virus is transmitted by Culicoides midges of the Obsoletus complex. SBV infection induces a solid protective immunity that persists for at least 4 or 6 years in sheep and cattle, respectively. SBV infection can be diagnosed directly by real-time RT-qPCR and virus isolation or indirectly by serological assays. Three vaccines are commercially available in Europe. This article provides a comprehensive literature review on this emerging disease regarding pathogenesis, transmission, diagnosis, control and prevention. This review also highlights that although much has been learned since SBV’s first emergence, there are still areas that require further study to devise better mitigation strategies.

Schmallenberg virus: a systematic international literature review (2011-2019) from an Irish perspective

In Autumn 2011, nonspecific clinical signs of pyrexia, diarrhoea, and drop in milk yield were observed in dairy cattle near the German town of Schmallenberg at the Dutch/German border. Targeted veterinary diagnostic investigations for classical endemic and emerging viruses could not identify a causal agent. Blood samples were collected from animals with clinical signs and subjected to metagenomic analysis; a novel orthobunyavirus was identified and named Schmallenberg virus (SBV). In late 2011/early 2012, an epidemic of abortions and congenital malformations in calves, lambs and goat kids, characterised by arthrogryposis and hydranencephaly were reported in continental Europe. Subsequently, SBV RNA was confirmed in both aborted and congenitally malformed foetuses and also in Culicoides species biting midges. It soon became evident that SBV was an arthropod-borne teratogenic virus affecting domestic ruminants. SBV rapidly achieved a pan-European distribution with most countries confirming SBV infection within a year or two of the initial emergence. The first Irish case of SBV was confirmed in the south of the country in late 2012 in a bovine foetus.

Since SBV was first identified in 2011, a considerable body of scientific research has been conducted internationally describing this novel emerging virus. The aim of this systematic review is to provide a comprehensive synopsis of the most up-to-date scientific literature regarding the origin of SBV and the spread of the Schmallenberg epidemic, in addition to describing the species affected, clinical signs, pathogenesis, transmission, risk factors, impact, diagnostics, surveillance methods and control measures. This review also highlights current knowledge gaps in the scientific literature regarding SBV, most notably the requirement for further research to determine if, and to what extent, SBV circulation occurred in Europe and internationally during 2017 and 2018. Moreover, recommendations are also made regarding future arbovirus surveillance in Europe, specifically the establishment of a European-wide sentinel herd surveillance program, which incorporates bovine serology and Culicoides entomology and virology studies, at national and international level to monitor for the emergence and re-emergence of arboviruses such as SBV, bluetongue virus and other novel Culicoides-borne arboviruses.

Survey to determine the farm-level impact of Schmallenberg virus during the 2016-2017 United Kingdom lambing season

Schmallenberg virus (SBV) causes abortions, stillbirths and fetal malformations in naïve ruminants. The impact of the initial outbreak (2011/2012) on British sheep farms has been previously investigated, with higher farmer perceived impacts and increased lamb and ewe mortality reported on SBV-affected farms. After several years of low, or no, circulation the UK sheep flock once again became vulnerable to SBV infection. Re-emergence was confirmed in autumn 2016. This study reports the analysis of a questionnaire designed to determine the farm-level impact of SBV on the 2016/2017 UK lambing period. Higher neonatal lamb mortality, dystocia and associated ewe deaths, and higher perceived impacts on sheep welfare, flock financial performance and farmer emotional wellness were reported on SBV confirmed (n=59) and SBV suspected (n=82), than SBV not suspected (n=74) farms. Additionally, although few farmers (20.4 per cent) reported previously vaccinating against SBV, the majority (78.3 per cent) stated they would vaccinate if purchasing at less than £1 per dose. These results are largely comparable to the findings reported for the 2011/2012 outbreak, highlighting the ongoing impact of SBV on sheep farms. If SBV continues to re-emerge cyclically, the economic and animal welfare costs to the UK sheep farming industry will continue.

Schmallenberg Virus: A Novel Virus of Veterinary Importance

In late 2011, unspecific clinical symptoms such as fever, diarrhea, and decreased milk production were observed in dairy cattle in the Dutch/German border region. After exclusion of classical endemic and emerging viruses by targeted diagnostic systems, blood samples from acutely diseased cows were subjected to metagenomics analysis. An insect-transmitted orthobunyavirus of the Simbu serogroup was identified as the causative agent and named Schmallenberg virus (SBV). It was one of the first detections of the introduction of a novel virus of veterinary importance to Europe using the new technology of next-generation sequencing. The virus was subsequently isolated from identical samples as used for metagenomics analysis in insect and mammalian cell lines and disease symptoms were reproduced in calves experimentally infected with both, this culture-grown virus and blood samples of diseased cattle. Since its emergence, SBV spread very rapidly throughout the European ruminant population causing mild unspecific disease in adult animals, but also premature birth or stillbirth and severe fetal malformation when naive dams were infected during a critical phase of gestation. In the following years, SBV recirculated regularly to a larger extend; in the 2014 and 2016 vector seasons the virus was again repeatedly detected in the blood of adult ruminants, and in the following winter and spring months, a number of malformed calves and lambs was born. The genome of viruses present in viremic adult animals showed a very high sequence stability; in sequences generated between 2012 and 2016, only a few amino acid substitutions in comparison to the initial SBV isolate could be detected. In contrast, a high sequence variability was identified in the aminoterminal part of the glycoprotein Gc-encoding region of viruses present in the brain of malformed newborns. This mutation hotspot is independent of the region or host species from which the samples originated and is potentially involved in immune evasion mechanisms.

Fetopathic effects of experimental Schmallenberg virus infection in pregnant goats

Schmallenberg virus (SBV) is an emerging virus responsible for congenital malformations in the offspring of domestic ruminants. It is speculated that infection of pregnant dams may also lead to a significant number of unrecognized fetal losses during the early period of gestation. To assess the pathogenic effects of SBV infection of goats in early pregnancy, we inoculated dams at day 28 or 42 of gestation and followed the animals until day 55 of gestation. Viremia in the absence of clinical signs was detected in all virus-inoculated goats. Fetal deaths were observed in several goats infected at day 28 or 42 of gestation and were invariably associated with the presence of viral genomic RNA in the affected fetuses. Among the viable fetuses, two displayed lesions in the central nervous system (porencephaly) in the presence of viral genome and antigen. All fetuses from goats infected at day 42 and the majority of fetuses from goats infected at day 28 of gestation contained viral genomic RNA. Viral genome was widely distributed in these fetuses and their respective placentas, and infectious virus could be isolated from several organs and placentomes of the viable fetuses. Our results show that fetuses of pregnant goats are susceptible to vertical SBV infection during early pregnancy spanning at least the period between day 28 and 42 of gestation. The outcomes of experimental SBV infection assessed at day 55 of gestation include fetal mortalities, viable fetuses displaying lesions of the central nervous system, as well as viable fetuses without any detectable lesion.

How is Europe positioned for a re-emergence of Schmallenberg virus?

Schmallenberg virus (SBV) caused a large scale epidemic in Europe from 2011 to 2013, infecting ruminants and causing foetal deformities after infection of pregnant animals. The main impact of the virus was financial loss due to restrictions on trade of animals, meat and semen. Although effective vaccines were produced, their uptake was never high. Along with the subsequent decline in new SBV infections and natural replacement of previously exposed livestock, this has resulted in a decrease in the number of protected animals. Recent surveillance has shown that a large population of naïve animals is currently present in Europe and that the virus is circulating at a low level. These changes in animal status, in combination with favourable conditions for insect vectors, may open the door to the re-emergence of SBV and another large scale outbreak in Europe. This review details the potential and preparedness for SBV re-emergence in Europe, discusses possible co-ordinated sentinel monitoring programmes for ruminant seroconversion and the presence of SBV in the insect vectors, and provides an overview of the economic impact associated with diagnosis, control and the effects of non-vaccination.

Generation and characterization of a potentially applicable Vero cell line constitutively expressing the Schmallenberg virus nucleocapsid protein

Schmallenberg virus (SBV) is a Culicoides-transmitted orthobunyavirus that poses a threat to susceptible livestock species such as cattle, sheep and goats. The nucleocapsid (N) protein of SBV is an ideal diagnostic antigen for the detection of viral infection. In this study, a stable Vero cell line, Vero-EGFP-SBV-N, constitutively expressing the SBV-N protein was established using a lentivirus system combined with puromycin selection. This cell line spontaneously emitted green fluorescent signals distributed throughout the cytoplasm, in which the expression of SBV-N fusion protein was confirmed by western blot analysis. The expression of SBV-N protein in Vero-EGFP-SBV-N cells was stable for more than fifty passages without puromycin pressure. The SBV-N fusion protein contained both an N-terminal enhanced green fluorescent protein (EGFP) tag and a C-terminal hexa-histidine (6 × His) tag, by which the N protein was successfully purified using Ni-NTA affinity chromatography. The cell line was further demonstrated to be reactive with SBV antisera and an anti-SBV monoclonal antibody in indirect immunofluorescence assays. Taken together, our results demonstrate that the Vero-EGFP-SBV-N cell line has potential for application in the serological diagnosis of SBV infection.

Seroprevalence of Schmallenberg virus infection in sheep and goats flocks in Germany, 2012-2013

Schmallenberg virus (SBV) is a member of the family Bunyaviridae and mainly affects ruminants. It is transmitted by biting midges, first and foremost Culicoides spp., and causes congenital malformations reflected in arthrogryposis-hydranencephaly (AH) syndrome. The aim of this study was to collect data on the emergence of SBV as a new arthropod-borne disease introduced into Europe in 2011. Germany was located in the core region of the 2011/2012 epidemic. Following two seroprevalence studies in the north-west of Germany in 2012, this study focused on the epidemiology and distribution of SBV throughout 130 small ruminant flocks in the whole country. Blood samples were obtained of 30 animals per flock and a SBV-specific questionnaire was used to collect operating data of the farms. The median within-herd seroprevalence for all 130 flocks tested was 53.3% with a total range from 0% to 100%. The median within-herd seroprevalence for goats was 30% [interquartile range (IQR): 40.3%] and 57% for sheep (IQR: 43.3%). Small ruminant flocks kept permanently indoors or housed overnight had a significantly lower seroprevalence than flocks kept permanently outdoors. In addition, this study revealed a significantly lower seroprevalence in the north-east of Germany. These results show that small ruminants in Germany are still at risk of contracting new SBV infections following incomplete seroconversion of flocks especially in the north-east of Germany. This might contribute to SBV becoming enzootic in central and northern Europe. Furthermore, the survey revealed that housing animals at least during mating and early pregnancy may reduce the risk of new SBV infections and may thus be an option to reduce losses as long as there is no licensed vaccine available on the German market.

Schmallenberg virus infection in South American camelids: Field and experimental investigations

During the first epizootic wave of the novel, teratogenic Schmallenberg virus (SBV, Orthobunyavirus) in ruminants in Northern Europe, serological evidence of a previous SBV-infection demonstrated that South American camelids (SAC) are also susceptible to SBV. However, their potential role in SBV spread remains unknown. To investigate the prevalence and course of SBV-infection in SAC, a German field study and an animal trial with three llamas and three alpacas were conducted. From September 2012 to December 2013, 313 of 502 SAC (62.35%) were found SBV seropositive, but negative for SBV-RNA. The estimated between-district (94.23% of 52) and median within-district (71.43%) and herd (73.13%) SBV seroprevalence in German SAC was similar to the seroprevalence reported in cattle herds and sheep flocks at the time. An age of >1 year was found a statistically significant risk factor for SBV-infection, which could be explained by the spatio-temporal spread of SBV in Germany during the study period. No clinical signs or an increase of abortion and congenital malformation associated with SBV-infection in SAC were reported by the study participants. Similar to SBV-infected ruminants, SBV-RNAemia in experimentally SBV-infected SAC was detected for a short time between days 3 and 7 after infection (dpi), and seroconversion occurred between 9 and 21 dpi. Despite the similar virological and serological results, the lack of clinical signs and congenital malformation associated with SBV-infection suggests that SBV causes subclinical infection in SAC. However, their role as reservoirs in the spread of SBV has to be further investigated.

Serological screening suggests presence of Schmallenberg virus in cattle, sheep and goat in the Zambezia Province, Mozambique

Schmallenberg virus (SBV) is a novel Orthobunyavirus within the family Bunyaviridae belonging to the Simbu serogroup. Schmallenberg virus infects ruminants and has since its discovery in the autumn 2011 been detected/spread to large parts of Europe. Most bunyaviruses are arboviruses, and SBV has been detected in biting midges in different European countries, suggesting that they may play a role in the transmission of the virus. It is not known how SBV was introduced to Europe and if SBV is present in countries outside of Europe. Thus, in this study, we conducted a serological screening for SBV antibodies in cattle (no. 79), sheep (no. 145) and goat (no. 141) in the Zambezia Province in Mozambique during September 2013. The results show a high percentage of antibody-positive animals. All farms tested had seropositive animals; cattle displayed the highest prevalence with 100% positive animals. Sheep and goat also displayed high number of positive animals with a 43–97% and 72–100% within-herd seroprevalence, respectively. This initial serological screening suggests that SBV is present on the African continent. However, cross-reactivity with other members of the Simbu serogroup cannot be ruled out, and further studies are needed to identify and characterize the virus responsible for the antibody-positive results.