Schmallenberg virus outbreak in the Netherlands: routine diagnostics and test results

Virus as Teratogenic Agents

Viral infectious diseases are important causes of reproductive disorders, as abortion, fetal mummification, embryonic mortality, stillbirth, and congenital abnormalities in animals and in humans. In this chapter, we provide an overview of some virus, as important agents in teratology.We begin by describing the Zika virus, whose infection in humans had a very significant impact in recent years and has been associated with major health problems worldwide. This virus is a teratogenic agent in humans and has been classified as a public health emergency of international concern (PHEIC).Then, some viruses associated with reproductive abnormalities on animals, which have a significant economic impact on livestock, are described, as bovine herpesvirus, bovine viral diarrhea virus, Schmallenberg virus, Akabane virus, and Aino virus.For all viruses mentioned in this chapter, the teratogenic effects and the congenital malformations associated with fetus and newborn are described, according to the most recent scientific publications.

Low incidence of Schmallenberg virus infection in natural cases of abortion in domestic ruminants in Hungary

An epizootic caused by a new orthobunyavirus called Schmallenberg virus (SBV) was recognised in European ruminants in 2011 and 2012. The re-emergence of the infection was reported in several countries in the subsequent years. Although the main clinical sign of SBV infection is abortion, the impact of SBV in natural cases of abortion in domestic ruminants had not been systematically examined before this study. The aim of the study was to investigate the role of SBV infection and to compare it to the importance of other causes of abortion by examining 537 natural cases of abortion that had occurred between 2011 and 2017 in Hungary. The cause of abortion was determined in 165 (31%) cases. An infectious cause was proved in 88 (16%) cases. SBV infection was found only in a total of four cases (0.8%) using real-time polymerase chain reaction. Three of them proved to be inapparent SBV infection, and one case was attributed to SBV-induced abortion by detecting non-purulent encephalitis and SBV nucleoprotein by immunohistochemistry in a brain tissue sample. According to the results, SBV played a minor role in natural cases of domestic ruminant abortion in Hungary during the 7-year period following the first SBV outbreak in 2011.

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.

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.

Viral emergence and consequences for reproductive performance in ruminants: two recent examples (bluetongue and Schmallenberg viruses)

Viruses can emerge unexpectedly in different regions of the world and may have negative effects on reproductive performance. This paper describes the consequences for reproductive performance that have been reported after the introduction to Europe of two emerging viruses, namely the bluetongue (BTV) and Schmallenberg (SBV) viruses. Following the extensive spread of BTV in northern Europe, large numbers of pregnant cows were infected with BTV serotype 8 (BTV-8) during the breeding season of 2007. Initial reports of some cases of abortion and hydranencephaly in cattle in late 2007 were followed by quite exhaustive investigations in the field that showed that 10%-35% of healthy calves were infected with BTV-8 before birth. Transplacental transmission and fetal abnormalities in cattle and sheep had been previously observed only with strains of the virus that were propagated in embryonated eggs and/or cell culture, such as vaccine strains or vaccine candidate strains. After the unexpected emergence of BTV-8 in northern Europe in 2006, another arbovirus, namely SBV, emerged in Europe in 2011, causing a new economically important disease in ruminants. This new virus, belonging to the Orthobunyavirus genus in the Bunyaviridae family, was first detected in Germany, in The Netherlands and in Belgium in 2011 and soon after in the UK, France, Italy, Luxembourg, Spain, Denmark and Switzerland. Adult animals show no or only mild clinical symptoms, whereas infection during a critical period of gestation can lead to abortion, stillbirth or the birth of severely malformed offspring. The impact of the disease is usually greater in sheep than in cattle. The consequences of SBV infection in domestic ruminants and more precisely the secondary effects on off-springs will be described.

Development and evaluation of an indirect enzyme-linked immunosorbent assay for serological detection of Schmallenberg virus antibodies in ruminants using whole virus antigen

Background

In late 2011, a new Orthobunyavirus of the Simbu serogroup named Schmallenberg virus (SBV) emerged in continental Europe. The virus is transmitted by hematophagous arthropods, with the Culicoides species as, so far known, main vectors. Infection with the virus can cause clinical signs in adult ruminants including diarrhea, fever and reduced milk production. Transplacental infection of the developing fetus can lead to malformations of varying severity. To assess seroprevalence of SBV in Sweden an indirect enzyme-linked immunosorbent assay (ELISA) was established in connection with the surveys. Here, we describe the development and evaluation of the indirect ELISA, based on whole virus as the coating antigen and a monoclonal antibody for the detection of antibodies to SBV in ruminant sera. The evaluation includes comparison between the in-house ELISA, virus neutralization test and an indirect commercial ELISA.

Results

The optimal working dilutions of antigens and conjugate were estimated with checkerboard titrations. Comparative studies, including ROC analyses, were used for the selection of an optimal cut-off (S/P value = sample value as percentage of positive control value). With an estimated S/P value of 15% the whole virus ELISA showed a specificity of 100% and a sensitivity of 99.19% compared to virus neutralization test (VNT) and with a good consistency as shown in reproducibility and variability experiments. Furthermore, the comparison of our whole virus indirect ELISA to an indirect ELISA with a SBV nucleoprotein antigen, demonstrated a higher sensitivity of our test.

Conclusion

The indirect whole virus ELISA described in this paper is a readily available test for serological analysis of SBV antibodies. Since this in-house ELISA demonstrates a specificity and sensitivity comparable to virus neutralization test and also shows a higher sensitivity compared to commercially available indirect ELISA, it is a useful alternative for surveillance and screening purposes of SBV.

Ovine and Bovine Congenital Abnormalities Associated With Intrauterine Infection With Schmallenberg Virus

In December 2011, a previously unknown congenital syndrome of arthrogryposis and hydranencephaly in sheep and cattle appeared in the Netherlands as an emerging epizootic due to Schmallenberg virus (SBV). Gross lesions in 102 lambs and 204 calves included porencephaly, hydranencephaly, cerebellar dysplasia and dysplasia of the brainstem and spinal cord, a flattened skull with brachygnathia inferior, arthrogryposis, and vertebral column malformations. Microscopic lesions in the central nervous system showed rarefaction and cavitation in the white matter, as well as degeneration, necrosis, and loss of neurons in the gray matter. Brain and spinal cord lesions were more severe in lambs than in calves. Ovine and bovine cases examined early in the outbreak showed encephalomyelitis. SBV infection was confirmed by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) in brain samples in 46 of 102 lambs (45%) and in 32 of 204 calves (16%). Immunohistochemistry, performed on tissue samples from 18 RT-qPCR-positive lambs, confirmed the presence of bunyaviral antigen in neurons of the brain in 16 cases. SBV antibodies were detected by enzyme-linked immunosorbent assay in fetal blood in 56 of 61 sampled ovine cases (92%). In a virus neutralization test, all tested dams of affected newborns, 46 ewes and 190 cows, were seropositive. Compared with other teratogenic viral infections, the pathogenesis and lesions of SBV in sheep and cattle fetuses are similar to those of other ruminant orthobunyaviruses. However, the loss of spinal ventral motor neurons and their tracts, resulting in micromyelia, distinguishes SBV infection from other viral central nervous system lesions in newborn ruminants.

Natural infection of pregnant cows with Schmallenberg virus--a follow-up study

Schmallenberg virus (SBV), an orthobunyavirus discovered in European livestock in late 2011 for the first time, causes premature or stillbirth and severe fetal malformation when cows and ewes are infected during pregnancy. Therefore, cattle of two holdings in the initially most affected area in Germany were closely monitored to describe the consequence for fetuses and newborn calves. Seventy-one calves whose mothers were naturally infected during the first five months of pregnancy were clinically, virologically, and serologically examined. One calve showed typical malformation, another one, born without visible abnormalities, was dead. Two cows aborted during the studied period; spleen and brain samples or meconium swabs were tested by real-time PCR, in none of the fetuses SBV-specific RNA was detectable and the tested fetal sera were negative in a commercially available antibody ELISA. In contrast, in nine clinically healthy calves high SBV-antibody titers were measurable before colostrum intake, and in meconium swabs of six of these animals viral RNA was present as well. The mothers of all nine seropositive calves were presumably infected between days 47 and 162 of gestation, which is within the critical timeframe for fetal infection suggested for SBV and related viruses.

Schmallenberg virus epidemic: impact on milk production, reproductive performance and mortality in dairy cattle in the Netherlands and Kleve district, Germany

Schmallenberg virus (SBV), a novel orthobunyavirus that rapidly spread throughout north-western Europe in 2011, caused congenital malformations in lambs and goat kids (Van den Brom et al., 2012) and newborn calves (Hoffmann et al., 2012). The impact of the SBV epidemic seemed limited however, in terms of the number of affected herds with malformed offspring (European Food Safety Authority, 2012b). Nevertheless, little is known with regard to the overall within-herd impact of SBV infection. The objective of the current study was to quantify the impact of the 2011 SBV epidemic on the productivity of dairy cattle in the Netherlands and the district of Kleve, Germany. For the Netherlands, several multilevel multivariable statistical models were applied on eight productivity parameters regarding milk production, reproductive performance and mortality. All four fertility parameters analysed were slightly but significantly reduced between August 1st and November 1st 2011 compared to the reference period in 2009-2010. Between August 15th and September 19th 2011, the average loss in milk production per cow was -0.26kg (95% CI: -0.30; -0.22) per day in dairy herds, compared to the reference period (p<0.001). The total loss per cow in a subgroup of dairy herds that notified malformations in newborn calves during the mandatory notification period in the Netherlands was -0.43kg (95% CI: -0.59; -0.28) per day (p<0.001). For Germany, a study was carried out in the district of Kleve, situated in the state of North Rhine-Westphalia near the Dutch border. Data on milk yield, two fertility parameters and the number of rendered calves in this specific region were analysed. There was a small but significant increase in the number of secondary and third inseminations between August 1st and November 1st 2011, indicating reduced fertility. No significant change in calf mortality was observed in the assumed SBV period. Milk production at district level did not seem to be affected by SBV in August and September 2011. SBV had no or limited impact on mortality rates, which was as expected given the relatively mild expression of SBV in adult cows and the low incidence of notified malformations in newborn calves. Our results indicate that SBV had a limited impact on productivity of dairy cattle. However, the total economic impact of SBV on the ruminant industry not only consists of productivity caused losses; it is expected that international trade restrictions formed a larger part of the total economic impact.

Schmallenberg virus-two years of experiences

In autumn 2011, a novel species of the genus Orthobunyavirus of the Simbu serogroup was discovered close to the German/Dutch border and named Schmallenberg virus (SBV). Since then, SBV has caused a large epidemic in European livestock. Like other viruses of the Simbu serogroup, SBV is transmitted by insect vectors. Adult ruminants may show a mild transient disease, while an infection during a critical period of pregnancy can lead to severe congenital malformation, premature birth or stillbirth. The current knowledge about the virus, its diagnosis, the spread of the epidemic, the impact and the possibilities for preventing infections with SBV is described and discussed.

Schmallenberg virus in Dutch dairy herds: potential risk factors for high within-herd seroprevalence and malformations in calves, and its impact on productivity

In November 2011, the new orthobunyavirus Schmallenberg virus (SBV) was identified in dairy cows that had induced fever, drop in milk production and diarrhoea in the Netherlands (Muskens et al., 2012. Tijdschrift voor Diergeneeskunde 137, 112-115) and a drop in milk production in cows in Northwestern Germany (Hoffmann et al., 2012. Emerging Infectious Diseases 18 (3), 469-472), in August/September 2011. This study aimed at quantifying risk factors for high within-herd prevalence of SBV and SBV-induced malformations in newborn calves in dairy herds in the Netherlands. Additionally, the within-herd impact of SBV infection on mortality rates and milk production was estimated. A case-control design was used, including 75 clinically affected case herds and 74 control herds. Control herds were selected based on absence of malformations in newborn calves and anomalies in reproductive performance. SBV-specific within-herd seroprevalences were estimated. Risk factors for high within-herd SBV seroprevalence (>50%) and the probability of malformed newborn calves in a herd were quantified. In addition, within-herd impact of SBV with regard to milk production and mortality was estimated. Animal-level seroprevalence was 84.4% (95% confidence interval (CI): 70.8-92.3) in case herds and 75.8% (95% CI: 67.5-82.5) in control herds. Control herds that were completely free from SBV were not present in the study. Herds that were grazed in 2011 had an increased odds (OR 9.9; 95% CI: 2.4-41.2)) of a high seroprevalence (>50%) compared to herds that were kept indoors. Also, when grazing was applied in 2011, the odds of malformations in newborn calves tended to be 2.6 times higher compared to herds in which cattle were kept indoors. Incidence of malformations in newborn calves at herd level was associated with both within-herd seroprevalence and clinical expression of the disease in adult cattle. The rate of vertical transmission of SBV to the fetus once a dam gets infected seemed low. A total of 146 stillborn or malformed calves were submitted by 65 farmers during the study period, of which 19 were diagnosed as SBV-positive based on pathological investigation and/or RT-qPCR testing of brain tissue. Based on these results combined with calving data from these herds we roughly estimated that at least 0.5% of the calves born between February and September 2012 have been infected by SBV. A drop in milk production was observed between the end of August 2011 and the first half of September (week 35-36), indicating the acute phase of the epidemic. During a 4-week period in which SBV infection was expected to have occurred, the total loss in milk production in affected dairy herds was around 30-51 kg per cow. SBV had no or limited impact on mortality rates which was as expected given the relatively mild expression of SBV in adult cows and the low incidence of malformations in newborn calves.

Genetic characterization of an atypical Schmallenberg virus isolated from the brain of a malformed lamb

A novel orthobunyavirus, named "Schmallenberg virus" (SBV), was first detected in the blood of cattle at the end of the summer in Germany in 2011, and subsequently in late autumn from the brain of a stillborn malformed lamb in The Netherlands. Full genome sequences, including 5' and 3' terminal "panhandle" sequences of the L, M, and S segments of the SBV isolated from lamb brain tissue (named HL1) were determined. In addition, a second SBV strain was isolated from the blood of a dairy cow (named F6) also in The Netherlands. This isolate was passaged on Vero cells, and its genome sequence was determined by next-generation sequencing. Alignments of the two genome sequences revealed 4, 12, and 2 amino acid differences in the open reading frames of the L, M, and S segments, respectively. Eleven of a total of 12 amino acid differences were detected in the M segment encoding the ectodomain of the putative structural glycoprotein Gc. Notably, in the HL1 isolate, positions 737-739 are occupied by isoleucine, arginine, and leucine (IRL), whereas in the majority of other sequenced SBV isolates these positions are occupied by threonine, histidine, and proline, respectively. Moreover, in all sheep, goat, and cattle SBV isolates sequenced and published so far, an IRL sequence was never found. This has brought us to the conclusion that the M segment of the HL1 isolate differed markedly from that of other lamb and cow isolates. Whether this atypical variant resulted from adaptation to the ewe, fetus, or insect vector remains to be investigated.

Evidence of Schmallenberg virus circulation in ruminants in Greece

During March 2013, we investigated the presence and the levels of Schmallenberg virus (SBV) circulation in three dairy cow herds and three sheep flocks in Central Macedonia, Greece. In two cow herds, a high number of abortions had been observed during the winter. Six bulk-tank milk samples and 147 individual sera were screened for SBV-specific antibodies by ELISA. Positive reactions were obtained from 5 out of 6 bulk-tank milk samples, 58 out of 90 sera from the 3 cow herds, and 2 sera from 2 of the 3 sheep flocks. Twenty-two ELISA-positive sera were tested by serum neutralization test (SNT). SNT confirmed the presence of neutralizing antibodies against SBV in all samples tested, with titers ranging between 1:32 and ≥1:256. No neutralizing antibodies against Akabane virus (AKAV) or Shamonda virus (SHAV) were detected, indicating that neutralizing antibodies against SBV do not cross react with AKAV or SHAV in SNT. ELISA testing of bulk-tank milk samples proved to be convenient and reliable. None of the tested sera was found positive for SBV by real-time RT-PCR, indicating that the sampling was conducted past the viremia stage. This is the first report of SBV circulation in Greece.