Preliminary estimate of Schmallenberg virus infection impact in sheep flocks - France

A Review on Reliable and Standardized Animal Models to Study the Pathogenesis of Schmallenberg Virus in Ruminant Natural Host Species

In the late summer of 2011, the Netherlands reported a cluster of reduced milk yield, fever, and diarrhea in dairy cattle. In March 2012, congenital malformations appeared, and Schmallenberg virus (SBV) was identified, becoming one of the few orthobunyaviruses distributed in Europe. Initially, little was known about the pathogenesis and epidemiology of these viruses in the European context, so assumptions were largely extrapolated from related viruses and other regions worldwide. To study SBV's pathogenesis and its ability to cross the placental barrier, standardized and repeatable models that mimic clinical signs observed in the field are essential. This review discusses some of the latest experimental designs for infectious disease challenges involving SBV, covering infectious doses, routes of infection, inoculum preparation, and origin. Special attention is given to the placental crossing associated with SBV.

More than a decade of research on Schmallenberg virus-Knowns and unknowns

Schmallenberg virus, an arbovirus of the Orthobunyavirus genus that primarily infects ruminants, emerged in 2011 near the Dutch-German border region and subsequently caused a large number of abortions and the births of severely malformed newborns in the European livestock population. Immediate intensive research led to the development of reliable diagnostic tests, the identification of competent Culicoides vector species, and the elucidation of the pathogenesis in infected vertebrate hosts. In addition, the structure of the major antigenic domain has been elucidated in great detail, leading to the development of effective marker vaccine candidates. The knowledge gained over the last decade on the biology and pathogenesis of SBV and the experience acquired in its control will be of great value in the future for the control of any similar emerging pathogen of veterinary or public health importance such as Shuni or Oropouche virus. However, some important knowledge gaps remain, for example, the factors contributing to the highly variable transmission rate from dam to fetus or the viral factors responsible for the vector competence of Culicoides midges are largely unknown. Thus, questions still remain for the next decade of research on SBV and related viruses.

Microcephaly and hydrocephalus in a sheep fetus infected with Neospora caninum in Southern Brazil - Short communication

A case of non-communicating hydrocephalus and microcephaly in a sheep fetus infected with Neospora caninum from Lages, Santa Catarina, Brazil, is reported. Macroscopically, there was moderate flattening and narrowing of the skull, and the portion of the cerebral hemispheres was markedly reduced in size, measuring 3.5 × 3.5 × 0.5 cm, with marked diffuse flattening of the brain gyri and dilation of the lateral ventricles. Cerebrospinal fluid samples were positive to N. caninum detection by PCR. Histologically, there was discrete focal lymphoplasmacytic necrotising encephalitis on the floor of the lateral ventricle, discrete multifocal gliosis and discrete multifocal lymphoplasmacytic myositis. Through the molecular detection of N. caninum in the cerebrospinal fluid, it was possible to report what appears to be the first case of non-communicating hydrocephalus and microcephaly in an ovine fetus infected with N. caninum.

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 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.

Reliable and Standardized Animal Models to Study the Pathogenesis of Bluetongue and Schmallenberg Viruses in Ruminant Natural Host Species with Special Emphasis on Placental Crossing

Starting in 2006, bluetongue virus serotype 8 (BTV8) was responsible for a major epizootic in Western and Northern Europe. The magnitude and spread of the disease were surprisingly high and the control of BTV improved significantly with the marketing of BTV8 inactivated vaccines in 2008. During late summer of 2011, a first cluster of reduced milk yield, fever, and diarrhoea was reported in the Netherlands. Congenital malformations appeared in March 2012 and Schmallenberg virus (SBV) was identified, becoming one of the very few orthobunyaviruses distributed in Europe. At the start of both epizootics, little was known about the pathogenesis and epidemiology of these viruses in the European context and most assumptions were extrapolated based on other related viruses and/or other regions of the World. Standardized and repeatable models potentially mimicking clinical signs observed in the field are required to study the pathogenesis of these infections, and to clarify their ability to cross the placental barrier. This review presents some of the latest experimental designs for infectious disease challenges with BTV or SBV. Infectious doses, routes of infection, inoculum preparation, and origin are discussed. Particular emphasis is given to the placental crossing associated with these two viruses.

Fetal infection with Schmallenberg virus - An experimental pathogenesis study in pregnant cows

Since its first appearance in 2011, Schmallenberg virus (SBV) has been repeatedly detected in aborted ruminant foetuses or severely malformed newborns whose mothers were naturally infected during pregnancy. However, especially the knowledge about dynamics of foetal infection in cattle is still scarce. Therefore, a total of 36 pregnant heifers were experimentally infected during two animal trials with SBV between days 60 and 150 of gestation. The foetuses were collected between 10 and 35 days after infection and virologically and pathologically investigated. Overall, 33 heifers yielded normally developed, macroscopically inconspicuous foetuses, but abundant virus replication was evident at the maternal/foetal interface and viral genome was detectable in at least one organ system of 18 out of 35 foetuses. One heifer was found to be not pregnant at autopsy. One of the animals aborted at day 4 after infection, viral RNA was detectable in the lymphatic tissue of the dam, in the maternal and foetal placenta, and in organs and lymphatic tissue of the foetus. In another foetus, SBV typical malformations like torticollis and arthrogryposis were observed. The corresponding dam was infected at day 90 of pregnancy and viral genome was detectable in the cerebellum of the unborn. Interestingly, no common patterns of infected foetal organs or maternal/foetal placentas could be identified, and both, sites of virus replication and genome loads, varied to a high degree in the individual foetuses. It is therefore concluded, that SBV infects in many cases also the bovine foetus of naïve pregnant cattle, however, the experimentally observed low abortion/malformation rate is in concordance to the reported low rates in the field during the first outbreak wave following the introduction of SBV. This observation speaks for a natural resistance of most bovine foetuses even during the vulnerable phase of early pregnancy, which has to be further studied in the future.

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.

Akabane, Aino and Schmallenberg virus-where do we stand and what do we know about the role of domestic ruminant hosts and Culicoides vectors in virus transmission and overwintering?

Akabane, Aino and Schmallenberg virus belong to the Simbu serogroup of Orthobunyaviruses and depend on Culicoides vectors for their spread between ruminant hosts. Infections of adults are mostly asymptomatic or associated with only mild symptoms, while transplacental crossing of these viruses to the developing fetus can have important teratogenic effects. Research mainly focused on congenital malformations has established a correlation between the developmental stage at which a fetus is infected and the outcome of an Akabane virus infection. Available data suggest that a similar correlation also applies to Schmallenberg virus infections but is not yet entirely conclusive. Experimental and field data furthermore suggest that Akabane virus is more efficient in inducing congenital malformations than Aino and Schmallenberg virus, certainly in cattle. The mechanism by which these Simbu viruses cross-pass yearly periods of very low vector abundance in temperate climate zones remains undefined. Yearly wind-borne reintroductions of infected midges from tropical endemic regions with year-round vector activity have been proposed, just as overwintering in long-lived adult midges. Experimental and field data however indicate that a role of vertical virus transmission in the ruminant host currently cannot be excluded as an overwintering mechanism. More studies on Culicoides biology and specific groups of transplacentally infected newborn ruminants without gross malformations are needed to shed light on this matter.

Schmallenberg disease in sheep or goats: Past, present and future

Schmallenberg disease has emerged in North-Western Europe in 2011 and has since spread widely, even across the European borders. It has the potency to infect many, mainly ruminant, species, but seems to lack zoonotic potential. Horizontal transmission occurs through various Culicoides biting midges and subsequent trans-placental transmission causes teratogenic effects. In some small ruminants, clinical signs, including fever, decreased milk production and diarrhea occur during the viraemic phase, but infection is mostly asymptomatic. However, fetal Schmallenberg virus infection in naïve ewes and goats can result in stillborn offspring, showing a congenital arthrogryposis-hydranencephaly syndrome. The economic impact of infection depends on the number of malformed lambs, but is generally limited. There is debate on whether Schmallenberg virus has newly emerged or is re-emerging, since it is likely one of the ancestors of Shamonda virus, both Orthobunyaviruses belonging to the species Sathuperi virus within the Simbu serogroup viruses. Depending on the vector-borne transmission and the serologic status, future outbreaks of Schmallenberg disease induced congenital disease are expected.

Seroprevalence of Schmallenberg virus in the United Kingdom and the Republic of Ireland: 2011-2013

Since its identification in late 2011, Schmallenberg virus (SBV) spread rapidly across Europe. Using archived samples from domestic ruminants collected between October 2011 and June 2013, the seroprevalence in the United Kingdom (UK) and Republic of Ireland (IE) was estimated using a serum neutralisation test. There was no significant difference (P>0.05) in seroprevalence between sheep and cows suggesting that neither species is significantly more at risk of SBV infection in the UK. A single 2011 sample tested positive; the sample was taken in November from a cow in Wiltshire. There was a steady increase in overall seroprevalence during the first three quarters of 2012, which then more than doubled in quarter 4 (October-December), which may reflect a peak of vector activity. By the end of June 2013, overall seroprevalence was around 72%. However, although seroprevalence was over 50% in Wales and southern and central counties of England, it was below 50% in all other areas of the UK and IE. This suggests that there were still substantial numbers of animals at risk of infection in the latter half of 2013.

Preparation and characterization of a stable BHK-21 cell line constitutively expressing the Schmallenberg virus nucleocapsid protein

Schmallenberg virus (SBV) is a newly emerged orthobunyavirus that predominantly infects livestock such as cattle, sheep, and goats. Its nucleocapsid (N) protein is an ideal target antigen for SBV diagnosis. In this study, a stable BHK-21 cell line, BHK-21-EGFP-SBV-N, constitutively expressing the SBV N protein was obtained using a lentivector-mediated gene transfer system combined with puromycin selection. To facilitate the purification of recombinant SBV N protein, the coding sequence for a hexa-histidine tag was introduced into the C-terminus of the SBV N gene during construction of the recombinant lentivirus vector pLV-EGFP-SBV-N. The BHK-21-EGFP-SBV-N cell line was demonstrated to spontaneously emit strong enhanced green fluorescent protein (EGFP) signals that exhibited a discrete punctate distribution throughout the cytoplasm. SBV N mRNA and protein expression in this cell line were detected by real-time RT-PCR and western blot, respectively. The expressed recombinant SBV N protein carried an N-terminal EGFP tag, and was successfully purified using Ni-NTA agarose by means of its C-terminal His tag. The purified SBV N protein could be recognized by SBV antisera and an anti-SBV monoclonal antibody (mAb) 2C8 in an indirect enzyme-linked immunosorbent assay and western blot analyses. Indirect immunofluorescence assays further demonstrated that the stable cell line reacts with SBV antisera and mAb 2C8. These results suggest that the generated cell line has the potential to be used in the serological diagnosis of SBV.

Was the French clinical surveillance system of bovine brucellosis influenced by the occurrence and surveillance of other abortive diseases?

The bovine brucellosis clinical surveillance system implemented in France aims to detect early any case of bovine brucellosis, a disease of which the country has been declared free since 2005. It relies on the mandatory notification of every bovine abortion. Following the spread of the Schmallenberg virus (SBV) in France in 2012 and 2013, and the implementation in 2012 of a clinical surveillance programme of Q fever based on abortion notifications in ten pilot départements, our objective was to study whether these two events influenced the brucellosis clinical surveillance system. The proportion of notifying farmers was analyzed over each semester from June 1, 2009 to June 30, 2013 according to the size and production type of herds, SBV status of départements and the implementation of the Q fever surveillance. Our analysis showed a slight increase in the proportion of notifying farmers as départements became infected by SBV, and after the implementation of Q fever surveillance (during the first semester of 2013). These variations might be explained by an increase in abortion occurrence (congenital deformities in newborns, due to SBV) and/or by an increase in farmers' and veterinarians' awareness (due to the spread of SBV and the implementation of the Q fever surveillance). These results highlight the difficulties in interpreting variations in the proportion of notifying farmers as a consequence of an increase in abortion occurrence. As bovine abortion surveillance can play an important role in the early warning for several diseases, there is a need to explore other ways to monitor abortions in cattle, such as syndromic surveillance using the dates of artificial insemination or calving data.

Spread and impact of the Schmallenberg virus epidemic in France in 2012-2013

Background

The Schmallenberg virus (SBV) emerged in Europe in 2011 and caused a widespread epidemic in ruminants.

In France, SBV emergence was monitored through a national multi-stakeholder surveillance and investigation system. Based on the monitoring data collected from January 2012 to August 2013, we describe the spread of SBV in France during two seasons of dissemination (vector seasons 2011 and 2012) and we provide a large-scale assessment of the impact of this new disease in ruminants.

Results

SBV impact in infected herds was primarily due to the birth of stillborns or deformed foetuses and neonates. Congenital SBV morbidity level was on average moderate, although higher in sheep than in other ruminant species. On average, 8% of lambs, 3% of calves and 2% of kids born in SBV-infected herds showed typical congenital SBV deformities. In addition, in infected herds, farmers reported retrospectively a lower prolificacy during the vector season, suggesting a potential impact of acute SBV infection during mating and early stages of gestation.

Conclusions

Due to the lack of available control and prevention measures, SBV spread quickly in the naive ruminant population. France continues to monitor for SBV, and updated information is made available online on a regular basis [http://www.plateforme-esa.fr/]. Outbreaks of congenital SBV are expected to occur sporadically from now on, but further epidemics may also occur if immunity at population level declines.

Schmallenberg virus infection among red deer, France, 2010-2012

Schmallenberg virus infection is emerging in European domestic and wild ruminants. We investigated the serologic status of 9 red deer populations to describe virus spread from September 2010 through March 2012 among wildlife in France. Deer in 7 populations exhibited seropositivity, with an average seroprevalence of 20%.

Generation of recombinant Schmallenberg virus nucleocapsid protein in yeast and development of virus-specific monoclonal antibodies

Schmallenberg virus (SBV), discovered in continental Europe in late 2011, causes mild clinical signs in adult ruminants, including diarrhoea and reduced milk yield. However, fetal infection can lead to severe malformation in newborn offspring. To develop improved reagents for SBV serology, a high-level yeast expression system was employed to produce recombinant SBV nucleocapsid (N) protein. Recombinant SBV N protein was investigated as an antigen in SBV-specific IgG enzyme immunoassay and used for generation of monoclonal antibodies (MAbs). Yeast-expressed SBV N protein was reactive with anti-SBV IgG-positive cow serum specimens collected from different farms of Lithuania. After immunization of mice with recombinant SBV N protein, four MAbs were generated. The MAbs raised against recombinant SBV N protein reacted with native viral nucleocapsids in SBV-infected BHK cells by immunofluorescence assay. The reactivity of recombinant N protein with SBV-positive cow serum specimens and the ability of the MAbs to recognize virus-infected cells confirm the antigenic similarity between yeast-expressed SBV N protein and native viral nucleocapsids. Our study demonstrates that yeast expression system is suitable for high-level production of recombinant SBV N protein and provides the first evidence on the presence of SBV-specific antibodies in cow serum specimens collected in Lithuania.

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.

Impact of Schmallenberg virus on British sheep farms during the 2011/2012 lambing season

British sheep farmers were invited to complete a questionnaire about the impact of Schmallenberg virus (SBV) on animal health, welfare and their own emotional wellbeing during the 2011–2012 lambing season, through Defra and Farming Industry websites, letters to farmers who had requested SBV laboratory tests and advertisement at Sheep 2012. The 494 responders included SBV confirmed (positive by RT-PCR) (n=76), SBV suspected by farmer (n=140) or SBV not suspected (n=278). Percentage of barren ewes was similar across SBV groups, however, lamb and ewe losses were higher on responder farms where SBV was confirmed or suspected. The median percentages of all lambs born (and lambs born deformed ) that died within one week of birth was 10.4 per cent (5.5 per cent), 7.0 per cent (2.9 per cent) and 5.3 per cent (0 per cent), respectively, on SBV confirmed, suspected and not suspected farms (P<0.001). Eight to 16 per cent of SBV confirmed or suspected farms reported lamb mortality of ≥40 per cent. Farmer perceived impact was greater where SBV was confirmed or suspected (P<0.001): 25 per cent reported a high impact on emotional wellbeing (4 per cent of SBV not suspected), 13 per cent reported a high impact on flock welfare and financial performance and 6 per cent were less likely to farm sheep next year because of SBV (<2 per cent in SBV not suspected). Overall, SBV impact has been large relative to reported sheep loss.

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.

Likely Introduction Date of Schmallenberg Virus into France According to Monthly Serological Surveys in Cattle

To estimate the date of introduction of Schmallenberg virus (SBV) into France, the prevalence of antibodies against the virus was determined monthly in cattle from two northern departments from August 2011 to April 2012. Seropositive cattle were detected from October 2011 in both departments with a prevalence of 55.6% in the westernmost department (Meurthe-et-Moselle) and of 12.7% in the easternmost department (Manche). Schmallenberg virus seroprevalence then increased rapidly to high levels.

The influence of the wind in the Schmallenberg virus outbreak in Europe

A model previously developed for the wind-borne spread by midges of bluetongue virus in NW Europe in 2006 is here modified and applied to the spread of Schmallenberg virus in 2011. The model estimates that pregnant animals were infected 113 days before producing malformed young, the commonest symptom of reported infection, and explains the spatial and temporal pattern of infection in 70% of the 3,487 affected farms, most of which were infected by midges arriving through downwind movement (62% of explained infections), or a mixture of downwind and random movements (38% of explained infections), during the period of day (1600–2100 h, i.e. dusk) when these insects are known to be most active. The main difference with Bluetongue is the higher rate of spread of SBV, which has important implications for disease control.

Schmallenberg virus detection in bovine semen after experimental infection of bulls

To study Schmallenberg virus (SBV) excretion in bovine semen after experimental infection, two bulls were inoculated subcutaneously with a SBV isolate (1 ml Vero cell culture 10⁶ TCID₅₀). After inoculation (at day 0), semen was collected daily from both animals for 21 days and samples were tested for SBV by qRT–PCR assay. At 24 days post-inoculation both animals were subjected to necropsy and the genital organs and lymph nodes draining these organs were also tested for SBV RNA (qRT–PCR). After SBV infection both animals in the study showed viraemia (qRT–PCR) with fever and diarrhoea. SBV RNA could be detected in semen from both animals. The highest SBV RNA concentrations in semen were found in the first week (days 4–7 post-inoculation) but concentrations were relatively low (Ct values 30–39). Viable SBV was only isolated from blood samples and not from semen or genital tissues.

Expression and purification of the nucleocapsid protein of Schmallenberg virus, and preparation and characterization of a monoclonal antibody against this protein

Schmallenberg virus (SBV) is a novel orthobunyavirus that primarily infects ruminants such as cattle, sheep and goats. The nucleocapsid (N) protein of SBV has been shown to be an ideal target antigen for serological detection. To prepare a monoclonal antibody (mAb) against the N protein, the full-length coding sequence of the SBV N gene was cloned into pET-28a-c(+) and pMAL-c5X vectors to generate two recombinant plasmids, which were expressed in Escherichia coli BL21 as histidine (His)-tagged (His-SBV-N) and maltose-binding protein (MBP)-tagged (MBP-SBV-N) fusion proteins, respectively. After affinity purification of His-SBV-N with Ni-NTA agarose and MBP-SBV-N with amylose resin, His-SBV-N was used to immunize BALB/c mice, while MBP-SBV-N was utilized to screen for mAb-secreting hybridomas. Six hybridoma cell lines stably secreting mAbs against N were obtained. Clone 2C8 was selected for further study because of its rapid growth characteristics in vitro and good reactivity with recombinant SBV N proteins in enzyme-linked immunosorbent assays. The epitope recognized by 2C8 is located at amino acids 51-76 of the SBV N protein. Western blot analyses showed that 2C8 reacts with both recombinant SBV N proteins and SBV isolates. It is also cross-reactive with the N proteins of genetically related Shamonda, Douglas and Akabane viruses, but not with the Rift Valley fever virus N protein. The successful preparation of recombinant N proteins and mAbs provides valuable materials that can be used in the serological diagnosis of SBV.

Schmallenberg virus experimental infection of sheep

Since late 2011, a novel orthobunyavirus, named Schmallenberg virus (SBV), has been implicated in many cases of severely malformed bovine and ovine offspring in Europe. In adult cattle, SBV is known to cause a mild transient disease; clinical signs include short febrile episodes, decreased milk production and diarrhoea for a few days. However, the knowledge about clinical signs and pathogenesis in adult sheep is limited. In the present study, adult sheep of European domestic breeds were inoculated with SBV either as cell culture grown virus or as virus with no history of passage in cell cultures. Various experimental set-ups were used. Sampling included blood collection at different time points during the experimental period and selected organ material at autopsy. Data from this study showed, that the RNAemic period in sheep was as short as reported for cattle; viral genome was detectable for about 3-5 days by real-time RT-PCR. In total, 13 out of 30 inoculated sheep became RNAemic, with the highest viral load in animals inoculated with virus from low cell culture passaged or the animal passaged material. Contact animals remained negative throughout the study. One RNAemic sheep showed diarrhoea for several days, but fever was not recorded in any of the animals. Antibodies were first detectable 10-14 days post inoculation. Viral RNA was detectable in spleen and lymph nodes up to day 44 post inoculation. In conclusion, as described for cattle, SBV-infection in adult sheep predominantly results in subclinical infection, transient RNAemia and a specific antibody response. Maintenance of viral RNA in the lymphoreticular system is observed for an extended period.

Epidemiology, molecular virology and diagnostics of Schmallenberg virus, an emerging orthobunyavirus in Europe

After the unexpected emergence of Bluetongue virus serotype 8 (BTV-8) in northern Europe in 2006, another arbovirus, Schmallenberg virus (SBV), emerged in Europe in 2011 causing a new economically important disease in ruminants. The 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 United Kingdom, France, Italy, Luxembourg, Spain, Denmark and Switzerland. This review describes the current knowledge on the emergence, epidemiology, clinical signs, molecular virology and diagnosis of SBV infection.

Where are the horses? With the sheep or cows? Uncertain host location, vector-feeding preferences and the risk of African horse sickness transmission in Great Britain

Understanding the influence of non-susceptible hosts on vector-borne disease transmission is an important epidemiological problem. However, investigation of its impact can be complicated by uncertainty in the location of the hosts. Estimating the risk of transmission of African horse sickness (AHS) in Great Britain (GB), a virus transmitted by Culicoides biting midges, provides an insightful example because: (i) the patterns of risk are expected to be influenced by the presence of non-susceptible vertebrate hosts (cattle and sheep) and (ii) incomplete information on the spatial distribution of horses is available because the GB National Equine Database records owner, rather than horse, locations. Here, we combine land-use data with available horse owner distributions and, using a Bayesian approach, infer a realistic distribution for the location of horses. We estimate the risk of an outbreak of AHS in GB, using the basic reproduction number (R0), and demonstrate that mapping owner addresses as a proxy for horse location significantly underestimates the risk. We clarify the role of non-susceptible vertebrate hosts by showing that the risk of disease in the presence of many hosts (susceptible and non-susceptible) can be ultimately reduced to two fundamental factors: first, the abundance of vectors and how this depends on host density, and, second, the differential feeding preference of vectors among animal species.

Oral exposure, reinfection and cellular immunity to Schmallenberg virus in cattle

Schmallenberg virus (SBV), a novel orthobunyavirus, was discovered in Germany in 2011. In adult ruminants SBV causes mild transient disease, but foetal infection can lead to severe malformations. Owing to its recent discovery, the knowledge about the pathogenesis is limited. In this study, two heifers seroconverted after a previous SBV infection and five SBV antibody-negative calves were subcutaneously inoculated, another two animals received SBV orally and three were kept as controls. In naïve cattle infected subcutaneously viral RNA was detected in serum and blood samples for several days. Seropositive or orally inoculated animals as well as the uninfected controls remained negative throughout the study. Seroconversion was observed only after subcutaneous exposure of the naïve animals to SBV. In lymphocytes from peripheral blood SBV genome was not detected, but the lymphocyte homeostasis in blood was influenced.

Schmallenberg virus pathogenesis, tropism and interaction with the innate immune system of the host

Schmallenberg virus (SBV) is an emerging orthobunyavirus of ruminants associated with outbreaks of congenital malformations in aborted and stillborn animals. Since its discovery in November 2011, SBV has spread very rapidly to many European countries. Here, we developed molecular and serological tools, and an experimental in vivo model as a platform to study SBV pathogenesis, tropism and virus-host cell interactions. Using a synthetic biology approach, we developed a reverse genetics system for the rapid rescue and genetic manipulation of SBV. We showed that SBV has a wide tropism in cell culture and "synthetic" SBV replicates in vitro as efficiently as wild type virus. We developed an experimental mouse model to study SBV infection and showed that this virus replicates abundantly in neurons where it causes cerebral malacia and vacuolation of the cerebral cortex. These virus-induced acute lesions are useful in understanding the progression from vacuolation to porencephaly and extensive tissue destruction, often observed in aborted lambs and calves in naturally occurring Schmallenberg cases. Indeed, we detected high levels of SBV antigens in the neurons of the gray matter of brain and spinal cord of naturally affected lambs and calves, suggesting that muscular hypoplasia observed in SBV-infected lambs is mostly secondary to central nervous system damage. Finally, we investigated the molecular determinants of SBV virulence. Interestingly, we found a biological SBV clone that after passage in cell culture displays increased virulence in mice. We also found that a SBV deletion mutant of the non-structural NSs protein (SBVΔNSs) is less virulent in mice than wild type SBV. Attenuation of SBV virulence depends on the inability of SBVΔNSs to block IFN synthesis in virus infected cells. In conclusion, this work provides a useful experimental framework to study the biology and pathogenesis of SBV.