Inactivated Schmallenberg virus prototype vaccines

Bunyavirales: Scientific Gaps and Prototype Pathogens for a Large and Diverse Group of Zoonotic Viruses

Research directed at select prototype pathogens is part of the approach put forth by the National Institute of Allergy and Infectious Disease (NIAID) to prepare for future pandemics caused by emerging viruses. We were tasked with identifying suitable prototypes for four virus families of the Bunyavirales order (Phenuiviridae, Peribunyaviridae, Nairoviridae, and Hantaviridae). This is a challenge due to the breadth and diversity of these viral groups. While there are many differences among the Bunyavirales, they generally have complex ecological life cycles, segmented genomes, and cause a range of human clinical outcomes from mild to severe and even death. Here, we delineate potential prototype species that encompass the breadth of clinical outcomes of a given family, have existing reverse genetics tools or animal disease models, and can be amenable to a platform approach to vaccine testing. Suggested prototype pathogens outlined here can serve as a starting point for further discussions.

Generation of Stable Cell Lines Expressing Akabane Virus N Protein and Insight into Its Function in Viral Replication

Akabane virus (AKAV) is a world wide epidemic arbovirus belonging to the Bunyavirales order that predominantly infects livestock and causes severe congenital malformations. The nucleocapsid (N) protein of AKAV possesses multiple important functions in the virus life cycle, and it is an ideal choice for AKAV detection. In this study, we successfully constructed two stable BHK-21 cell lines (C8H2 and F7E5) that constitutively express the AKAV N protein using a lentivirus system combined with puromycin selection. RT-PCR analysis confirmed that the AKAV N gene was integrated into the BHK-21 cell genome and consistently transcribed. Indirect immunofluorescence (IFA) and Western blot (WB) assays proved that both C8H2 and F7E5 cells could react with the AKAV N protein mAb specifically, indicating potential applications in AKAV detection. Furthermore, we analyzed the growth kinetics of AKAV in the C8H2 and F7E5 cell lines and observed temporary inhibition of viral replication at 12, 24 and 36 h postinfection (hpi) compared to BHK-21 cells. Subsequent investigations suggested that the reduced viral replication was linked to the down-regulation of the viral mRNAs (Gc and RdRp). In summary, we have established materials for detecting AKAV and gained new insights into the function of the AKAV N protein.

Comparison of Immunogenicity Between a Candidate Live Attenuated Vaccine and an Inactivated Vaccine for Cache Valley Virus

Cache Valley virus (CVV) is a mosquito-borne bunyavirus that is enzootic throughout the new world. Although CVV is known as an important agricultural pathogen, primarily associated with embryonic lethality and abortions in ruminants, it has recently been recognized for its expansion as a zoonotic pathogen. With the increased emergence of bunyaviruses with human and veterinary importance, there have been significant efforts dedicated to the development of bunyavirus vaccines. In this study, the immunogenicity of a candidate live-attenuated vaccine (LAV) for CVV, which contains the deletion of the nonstructural small (NSs) and nonstructural medium (NSm) genes (2delCVV), was evaluated and compared with an autogenous candidate vaccine created through the inactivation of CVV using binary ethylenimine (BEI) with an aluminum hydroxide adjuvant (BEI-CVV) in sheep. Both 2delCVV and BEI-CVV produced a neutralizing antibody response that exceeds the correlate of protection, that is, plaque reduction neutralization test titer >10. However, on day 63 postinitial immunization, 2delCVV was more immunogenic than BEI-CVV. These results warrant further development of 2delCVV as a candidate LAV and demonstrate that the double deletion of the NSs and NSm genes can be applied to the development of vaccines and as a common attenuation strategy for orthobunyaviruses.

Vaccine development against Schmallenberg virus: from classical inactivated to modified-live to scaffold particle vaccines

BACKGROUND

Subsequent to its first detection in 2011, the insect-transmitted bunyavirus Schmallenberg virus (SBV; genus Orthobunyavirus) caused a large-scale epizootic of fetal malformation in the European ruminant population. By now, SBV established an enzootic status in Central Europe with regular wave-like re-emergence, which has prompted intensive research efforts in order to elucidate the pathogenesis and to develop countermeasures. Since different orthobunyaviruses share a very similar structural organization, SBV has become an important model virus to study orthobunyaviruses in general and for the development of vaccines. In this review article, we summarize which vaccine formulations have been tested to prevent SBV infections in livestock animals. MAIN: In a first step, inactivated SBV candidate vaccines were developed, which efficiently protected against an experimental SBV infection. Due to the inability to differentiate infected from vaccinated animals (= DIVA capability), a series of further approaches ranging from modified live, live-vectored, subunit and DNA-mediated vaccine delivery to multimeric antigen-presentation on scaffold particles was developed and evaluated. In short, it was repeatedly demonstrated that the N-terminal half of the glycoprotein Gc, composed of the Gc head and the head-stalk, is highly immunogenic, with a superior immunogenicity of the complete head-stalk domain compared to the Gc head only. Furthermore, in all Gc protein-based vaccine candidates, immunized animals can be readily discriminated from animals infected with the field virus by the absence of antibodies against the viral N-protein.

CONCLUSIONS

Using SBV as a model virus, several vaccination-challenge studies in target species underscored the superior performance of antigenic domains compared to linear epitopes regarding their immunogenicity. In addition, it could be shown that holistic approaches combining immunization-challenge infection studies with structural analyses provide essential knowledge required for an improved vaccine design.

Baseline mapping of Oropouche virology, epidemiology, therapeutics, and vaccine research and development

Oropouche virus (OROV) is an arthropod-borne orthobunyavirus found in South America and causes Oropouche fever, a febrile infection similar to dengue. It is the second most prevalent arthropod-borne viral disease in South America after dengue. Over 500,000 cases have been diagnosed since the virus was first discovered in 1955; however, this is likely a significant underestimate given the limited availability of diagnostics. No fatalities have been reported to date, however, up to 60% of cases have a recurrent phase of disease within one month of recovery from the primary disease course. The main arthropod vector is the biting midge Culicoides paraensis, which has a geographic range as far north as the United States and demonstrates the potential for OROV to geographically expand. The transmission cycle is incompletely understood and vertebrate hosts include both non-human primates and birds further supporting the potential ability of the virus to spread. A number of candidate antivirals have been evaluated against OROV in vitro but none showed antiviral activity. Surprisingly, there is only one report in the literature on candidate vaccines. We suggest that OROV is an undervalued pathogen much like chikungunya, Schmallenberg, and Zika viruses were before they emerged. Overall, OROV is an important emerging disease that has been under-investigated and has the potential to cause large epidemics in the future. Further research, in particular candidate vaccines, is needed for this important pathogen.

Development of a Modular Vaccine Platform for Multimeric Antigen Display Using an Orthobunyavirus Model

Emerging infectious diseases represent an increasing threat to human and animal health. Therefore, safe and effective vaccines that could be available within a short time frame after an outbreak are required for adequate prevention and control. Here, we developed a robust and versatile self-assembling multimeric protein scaffold particle (MPSP) vaccine platform using lumazine synthase (LS) from Aquifex aeolicus. This scaffold allowed the presentation of peptide epitopes by genetic fusion as well as the presentation of large antigens by bacterial superglue-based conjugation to the pre-assembled particle. Using the orthobunyavirus model Schmallenberg virus (SBV) we designed MPSPs presenting major immunogens of SBV and assessed their efficacy in a mouse model as well as in cattle, a target species of SBV. All prototype vaccines conferred protection from viral challenge infection and the multivalent presentation of the selected antigens on the MPSP markedly improved their immunogenicity compared to the monomeric subunits. Even a single shot vaccination protected about 80% of mice from an otherwise lethal dose of SBV. Most importantly, the MPSPs induced a virtually sterile immunity in cattle. Altogether, LS represents a promising platform for modular and rapid vaccine design.

Differentiation of Antibodies against Selected Simbu Serogroup Viruses by a Glycoprotein Gc-Based Triplex ELISA

The Simbu serogroup of orthobunyaviruses includes several pathogens of veterinary importance, among them Schmallenberg virus (SBV), Akabane virus (AKAV) and Shuni virus (SHUV). They infect predominantly ruminants and induce severe congenital malformation. In adult animals, the intra vitam diagnostics by direct virus detection is limited to only a few days due to a short-lived viremia. For surveillance purposes the testing for specific antibodies is a superior approach. However, the serological differentiation is hampered by a considerable extent of cross-reactivity, as viruses were assigned into this serogroup based on antigenic relatedness. Here, we established a glycoprotein Gc-based triplex enzyme-linked immunosorbent assay (ELISA) for the detection and differentiation of antibodies against SBV, AKAV, and SHUV. A total of 477 negative samples of various ruminant species, 238 samples positive for SBV-antibodies, 36 positive for AKAV-antibodies and 53 SHUV antibody-positive samples were tested in comparison to neutralization tests. For the newly developed ELISA, overall diagnostic specificities of 84.56%, 94.68% and 89.39% and sensitivities of 89.08%, 69.44% and 84.91% were calculated for SBV, AKAV and SHUV, respectively, with only slight effects of serological cross-reactivity on the diagnostic specificity. Thus, this test system could be used for serological screening in suspected populations or as additional tool during outbreak investigations.

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.

Immunogenicity and efficacy of Schmallenberg virus envelope glycoprotein subunit vaccines

The Schmallenberg virus (SBV) is an orthobunyavirus that causes abortions, stillbirths, and congenital defects in pregnant sheep and cattle. Inactivated or live attenuated vaccines have been developed in endemic countries, but there is still interest in the development of SBV vaccines that would allow Differentiating Infected from Vaccinated Animals (DIVA). Therefore, an attempt was made to develop novel DIVA-compatible SBV vaccines using SBV glycoproteins expressed in baculovirus. All vaccines and phosphate buffered saline (PBS) controls were prepared with adjuvant and administered subcutaneously to cattle at 6 month of age. The first trial included 2 groups of animals vaccinated with either carboxyl-terminus glycoprotein (Gc) or PBS and boosted after 2 weeks. In the second trial, 3 groups of cattle were administered either Gc, Gc and amino-terminus glycoprotein (Gn), or PBS with a booster vaccination after 3 weeks. The animals were challenged with SBV 9 days after the booster vaccination in the first study, and 3 weeks after the booster vaccination in the second study. Using a SBV Gc-specific enzyme-linked immunosorbent assay, antibodies were first detected in serum samples 14 days after the first vaccination in both trials, and peaked on days 7 and 9 after the booster in the first and second trials, respectively. Low titers of neutralizing antibodies were detected in serum from only 3/6 and 2/4 animals in the first and second trial, respectively, at 14 days after the first vaccination. The titers increased 2 to 3-fold after the booster vaccination. SBV-specific RNA was detected in the serum and selective tissues in all animals after SBV challenge independent of vaccination status. The SBV candidate vaccines neither prevented viremia nor conferred protection against SBV infection.

Schmallenberg virus neutralising antibody responses in sheep

BACKGROUND

Schmallenberg virus (SBV) is a midge borne virus of cattle and sheep. Infection is typically asymptomatic in adult sheep but fetal infection during pregnancy can result in abortion, stillbirth, neurological disorders and malformations of variable severity in newborn animals. It was first identified in Germany and the Netherlands in 2011 and then circulated throughout Europe in 2012 and 2013. Circulation in subsequent years was low or non-existent until summer and autumn 2016, leading to an increased incidence of deformed newborn lambs and calves in 2016-17. This study reports SBV circulation in October 2016 within a group of 24 ewes and 13 rams. The ewes were monitored at 3 times points over an 11 week period (September to December 2016).

RESULTS

Most ewes displayed an increase in SBV VNT with antibody titre increases greater in older, previously exposed ewes. Two ewes had SBV RNA detectable by RT-qPCR, one on 30/09/16 and one on 04/11/16. Of these ewes, one had detectable serum SBV RNA (indicating viraemia) despite pre-existing antibody. The rams had been previously vaccinated with a commercial inactivated SBV vaccine, they showed minimal neutralising antibody titres against SBV 8 months post-vaccination and all displayed increased titre in October 2016.

CONCLUSION

This data suggests that SBV circulated for a minimum period of 5 weeks in September to October 2016 in central England. Ewes previously exposed to virus showed an enhanced antibody response compared to naïve animals. Pre-existing antibody titre did not prevent re-infection in at least one animal, implying immunity to SBV upon natural exposure may not be life-long. In addition, data suggests that immunity provided by killed adjuvanted SBV vaccines only provides short term protection (< 8 months) from virus.

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.

N-terminal domain of Schmallenberg virus envelope protein Gc delivered by recombinant equine herpesvirus type 1 and modified vaccinia virus Ankara: Immunogenicity and protective efficacy in cattle

Schmallenberg virus (SBV), which emerged in 2011 in Central Europe and subsequently spread very rapidly throughout the continent, affects predominantly ruminants. SBV is transmitted by insect vectors, and therefore vaccination is one of the major tools of disease control. Only recently, a domain connected to virus neutralization has been identified at the amino-terminal part of the viral envelope protein Gc. Here, this Gc domain delivered by recombinant EHV-1 or MVA vector viruses was tested in a vaccination-challenge trial in cattle, one of the major target species of SBV. The EHV-1-based vaccine conferred protection in two of four animals, whereas immunization using the MVA vector vaccine efficiently induced an SBV-specific antibody response and full protection against SBV challenge infection in all the vaccinated animals. Moreover, due to the absence of antibodies against SBVs N-protein, both vector vaccines enable the differentiation between vaccinated and field-infected animals making them to a promising tool to control SBV spread as well as to prevent disease in domestic ruminants.

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.

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.

DNA vaccination regimes against Schmallenberg virus infection in IFNAR-/- mice suggest two targets for immunization

Schmallenberg virus (SBV) is an RNA virus of the Bunyaviridae family, genus Orthobunyavirus that infects wild and livestock species of ruminants. While inactivated and attenuated vaccines have been shown to prevent SBV infection, little is known about their mode of immunity; specifically, which components of the virus are responsible for inducing immunological responses in the host. As previous DNA vaccination experiments on other bunyaviruses have found that glycoproteins, as well as modified (i.e. ubiquitinated) nucleoproteins (N) can confer immunity against virulent viral challenge, constructs encoding for fragments of SBV glycoproteins G_N and G_C, as well as ubiquitinated and non-ubiquitinated N were cloned in mammalian expression vectors, and vaccinated intramuscularly in IFNAR^-/- mice. Upon viral challenge with virulent SBV, disease progression was monitored. Both the ubiquitinated and non-ubiquitinated nucleoprotein candidates elicited high titers of antibodies against SBV, but only the non-ubiquitinated candidate induced statistically significant protection of the vaccinated mice from viral challenge. Another construct encoding for a putative ectodomain of glycoprotein G_C (segment aa. 678-947) also reduced the SBV-viremia in mice after SBV challenge. When compared to other experimental groups, both the nucleoprotein and G_C-ectodomain vaccinated groups displayed significantly reduced viremia, as well as exhibiting no clinical signs of SBV infection. These results show that both the nucleoprotein and the putative G_C-ectodomain can serve as protective immunological targets against SBV infection, highlighting that viral glycoproteins, as well as nucleoproteins are potent targets in vaccination strategies against bunyaviruses.

The N-terminal domain of Schmallenberg virus envelope protein Gc is highly immunogenic and can provide protection from infection

Schmallenberg virus (SBV) is transmitted by insect vectors, and therefore vaccination is one of the most important tools of disease control. In our study, novel subunit vaccines on the basis of an amino-terminal domain of SBV Gc of 234 amino acids (“Gc Amino”) first were tested and selected using a lethal small animal challenge model and then the best performing formulations also were tested in cattle. We could show that neither E. coli expressed nor the reduced form of “Gc Amino” protected from SBV infection. In contrast, both, immunization with “Gc Amino”-encoding DNA plasmids and “Gc-amino” expressed in a mammalian system, conferred protection in up to 66% of the animals. Interestingly, the best performance was achieved with a multivalent antigen containing the covalently linked Gc domains of both, SBV and the related Akabane virus. All vaccinated cattle and mice were fully protected against SBV challenge infection. Furthermore, in the absence of antibodies against the viral N-protein, differentiation between vaccinated and field-infected animals allows an SBV marker vaccination concept. Moreover, the presented vaccine design also could be tested for other members of the Simbu serogroup and might allow the inclusion of additional immunogenic domains.

Persistence of the protective immunity and kinetics of the isotype specific antibody response against the viral nucleocapsid protein after experimental Schmallenberg virus infection of sheep

Schmallenberg virus (SBV) is an Orthobunyavirus that induces abortion, stillbirths and congenital malformations in ruminants. SBV infection induces a long lasting seroconversion under natural conditions. The persistence of the protective immunity and the isotype specific antibody response upon SBV infection of sheep has however not been studied in detail. Five sheep were kept in BSL3 facilities for more than 16 months and subjected to repeated SBV infections. Blood was regularly sampled and organs were collected at euthanasia. The presence of SBV RNA in serum and organs was measured with quantitative real-time PCR. The appearance and persistence of neutralizing and SBV nucleoprotein (N) isotype specific antibodies was determined with virus neutralization tests (VNT) and ELISAs. The primo SBV infection protected ewes against clinical signs, viraemia and virus replication in organs upon challenge infections more than 15 months later. Production of neutralizing SBV specific antibodies was first detected around 6 days post primo-inoculation with VNT and correlated with the appearance of SBV-N specific IgM antibodies. These IgM antibodies remained present for 2 weeks. SBV-N specific IgG antibodies were first detected between 10 and 21 dpi and reached a plateau at 28 dpi. This plateau remained consistently high and no significant decrease in titre was found over a period of more than 1 year. Similar results were found for the neutralising antibody response. In conclusion, the SBV specific IgM response probably eliminates SBV from the blood and the protective immunity induced by SBV infection protects sheep against reinfection for at least 16 months.

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.

Deletion mutants of Schmallenberg virus are avirulent and protect from virus challenge

Since its emergence, Schmallenberg virus (SBV), a novel insect-transmitted orthobunyavirus which predominantly infects ruminants, has caused a large epidemic in European livestock. Newly developed inactivated vaccines are available, but highly efficacious and safe live vaccines are still not available. Here, the properties of novel recombinant SBV mutants lacking the nonstructural protein NSs (rSBVΔNSs) or NSm (rSBVΔNSm) or both of these proteins (rSBVΔNSs/ΔNSm) were tested in vitro and in vivo in type I interferon receptor knockout mice (IFNAR(-/-)) and in a vaccination/challenge trial in cattle. As for other bunyaviruses, both nonstructural proteins of SBV are not essential for viral growth in vitro. In interferon-defective BHK-21 cells, rSBVΔNSs and rSBVΔNSm replicated to levels comparable to that of the parental rSBV; the double mutant virus, however, showed a mild growth defect, resulting in lower final virus titers. Additionally, both mutants with an NSs deletion induced high levels of interferon and showed a marked growth defect in interferon-competent sheep SFT-R cells. Nevertheless, in IFNAR(-/-) mice, all mutants were virulent, with the highest mortality rate for rSBVΔNSs and a reduced virulence for the NSm-deleted virus. In cattle, SBV lacking NSm caused viremia and seroconversion comparable to those caused by the wild-type virus, while the NSs and the combined NSs/NSm deletion mutant induced no detectable virus replication or clinical disease after immunization. Furthermore, three out of four cattle immunized once with the NSs deletion mutant and all animals vaccinated with the virus lacking both nonstructural proteins were fully protected against a challenge infection. Therefore, the double deletion mutant will provide the basis for further developments of safe and efficacious modified live SBV vaccines which could be also a model for other viruses of the Simbu serogroup and related orthobunyaviruses.

IMPORTANCE

SBV induces only mild clinical signs in adult ruminants but causes severe fetal malformation and, thereby, can have an important impact on animal welfare and production. As SBV is an insect-transmitted pathogen, vaccination will be one of the most important aspects of disease control. Here, mutant viruses lacking one or two proteins that essentially contribute to viral pathogenicity were tested as modified live vaccines in cattle. It could be demonstrated that a novel recombinant double deletion mutant is a safe and efficacious vaccine candidate. This is the first description of a putative modified live vaccine for the complete genus Orthobunyavirus, and in addition, such a vaccine type has never been tested in cattle for any virus of the entire family Bunyaviridae. Therefore, the described vaccine also represents the first model for a broad range of related viruses and is of high importance to the field.

Orthobunyaviruses: recent genetic and structural insights

Orthobunyaviruses, which have small, tripartite, negative-sense RNA genomes and structurally simple virions composed of just four proteins, can have devastating effects on human health and well-being, either by causing disease in humans or by causing disease in livestock and crops. In this Review, I describe the recent genetic and structural advances that have revealed important insights into the composition of orthobunyavirus virions, viral transcription and replication and viral interactions with the host innate immune response. Lastly, I highlight outstanding questions and areas of future research.

Next-generation sequencing in veterinary medicine: how can the massive amount of information arising from high-throughput technologies improve diagnosis, control, and management of infectious diseases?

The development of high-throughput molecular technologies and associated bioinformatics has dramatically changed the capacities of scientists to produce, handle, and analyze large amounts of genomic, transcriptomic, and proteomic data. A clear example of this step-change is represented by the amount of DNA sequence data that can be now produced using next-generation sequencing (NGS) platforms. Similarly, recent improvements in protein and peptide separation efficiencies and highly accurate mass spectrometry have promoted the identification and quantification of proteins in a given sample. These advancements in biotechnology have increasingly been applied to the study of animal infectious diseases and are beginning to revolutionize the way that biological and evolutionary processes can be studied at the molecular level. Studies have demonstrated the value of NGS technologies for molecular characterization, ranging from metagenomic characterization of unknown pathogens or microbial communities to molecular epidemiology and evolution of viral quasispecies. Moreover, high-throughput technologies now allow detailed studies of host-pathogen interactions at the level of their genomes (genomics), transcriptomes (transcriptomics), or proteomes (proteomics). Ultimately, the interaction between pathogen and host biological networks can be questioned by analytically integrating these levels (integrative OMICS and systems biology). The application of high-throughput biotechnology platforms in these fields and their typical low-cost per information content has revolutionized the resolution with which these processes can now be studied. The aim of this chapter is to provide a current and prospective view on the opportunities and challenges associated with the application of massive parallel sequencing technologies to veterinary medicine, with particular focus on applications that have a potential impact on disease control and management.

Natural Immunity of Sheep and Lambs Against the Schmallenberg Virus Infection

Since the first reports of the Schmallenberg disease (SBD) outbreaks in late 2011, the disease has spread across Europe, affecting cattle and sheep farms. While Schmallenberg virus (SBV) causes a mild clinical disease in adults, infection of pregnant females may lead to the production of typical congenital malformations (CMFs) in their offspring. It is speculated that the immunity acquired after a SBV infection is effective in preventing further infections. However, this has not been proven in naturally infected sheep, especially if they are pregnant when reinfected. The aim of this study was to monitor the natural immunity in SBV-infected sheep. Twenty-four ewes from the only Spanish farm with a SBV OIE-notified outbreak were sampled. Subsequently, nine pregnant ewes were inoculated with SBV infectious plasma under controlled conditions. Six of them were euthanized before delivery, and their fetuses were inspected for lesions indicative for the SBV infection. The three remaining ewes were allowed to deliver one lamb each. Inoculation of the lambs was scheduled at approx. 3 months after birth. All samples were analyzed for viral RNA by RT-PCR, and for antibodies by an indirect ELISA and a virus neutralization test (VNT). The majority of the 24 ewes showed a serological reaction against SBV. The three ewes that were allowed to lamb down demonstrated variable degrees of seroconversion which corresponded to the levels of immune reaction observed in their lambs. Moreover, no viral RNA was detected, no lesions were observed in the fetuses, and no clinical signs were detected in the inoculated animals. These findings suggest that the immunity acquired by sheep following a natural SBV infection could be sufficient to stop SBV reinfection. However, vaccination could be a valuable tool to control SBV infections and associated economic losses as it affords a more uniform and predictable protection at the flock/herd level.

Single immunization with an inactivated vaccine protects sheep from Schmallenberg virus infection

The arthropod-borne Schmallenberg virus (SBV), family Orthobunyaviridae, emerged in Europe in 2011. SBV is associated with a mild disease in adult ruminants but fetal malformation after an infection during a critical phase of pregnancy. A number of inactivated vaccines have been developed; their efficacy after two injections was demonstrated. To make the vaccination of sheep more efficient and economic the effect of a single immunization with one of these vaccines was investigated in the present study. Five vaccinated sheep and five additional control sheep were inoculated with SBV three weeks after vaccination and the results of a competitive ELISA, a standard microneutralization test and an SBV-specific real-time RT-PCR confirmed vaccine efficacy by demonstrating complete inhibition of viral replication in immunized animals.

Impact of temperature, feeding preference and vaccination on Schmallenberg virus transmission in Scotland

First identified in 2011, Schmallenberg virus (SBV) is principally transmitted by Culicoides midges and affects ruminants. Clinical presentation is typified by foetal abnormalities, but despite very high infection rates, relatively few animals present with clinical signs. In this paper we further develop a previously published stochastic mathematical model of SBV spread to investigate the optimal deployment of a vaccine for SBV in Scotland, a country that has experienced only sporadic and isolated cases of SBV. We consider the use of the vaccine under different temperatures and explore the effects of a vector preference for feeding on cattle. We demonstrate that vaccine impact is optimised by targeting it at the high risk areas in the south of Scotland, or vaccinating only cattle. At higher than average temperatures, and hence increased transmission potential, the relative impact of vaccination is considerably enhanced. Vaccine impact is also enhanced if vectors feed preferentially on cattle. These findings are of considerable importance when planning control strategies for SBV and also have important implications for management of other arboviruses such as Bluetongue virus. Environmental determinants and feeding preferences should be researched further to inform development of effective control strategies.

Serosurveillance of Schmallenberg virus in Switzerland using bulk tank milk samples

Infections with Schmallenberg virus (SBV), a novel Orthobunyavirus transmitted by biting midges, can cause abortions and malformations of newborns and severe symptoms in adults of domestic and wild ruminants. Understanding the temporal and spatial distribution of the virus in a certain territory is important for the control and prevention of the disease. In this study, seroprevalence of antibodies against SBV and the spatial spread of the virus was investigated in Swiss dairy cattle applying a milk serology technique on bulk milk samples. The seroprevalence in cattle herds was significantly higher in December 2012 (99.5%) compared to July 2012 (19.7%). This high between-herd seroprevalence in cattle herds was observed shortly after the first detection of viral infections. Milk samples originating from farms with seropositive animals taken in December 2012 (n=209; mean 160%) revealed significantly higher S/P% ratios than samples collected in July 2012 (n=48; mean 103.6%). This finding suggests a high within-herd seroprevalence in infected herds which makes testing of bulk tank milk samples for the identification farms with past exposures to SBV a sensitive method. It suggests also that within-herd transmission followed by seroconversion still occurred between July and December. In July 2012, positive bulk tank milk samples were mainly restricted to the western part of Switzerland whereas in December 2012, all samples except one were positive. A spatial analysis revealed a separation of regions with and without positive farms in July 2012 and no spatial clustering within the regions with positive farms. In contrast to the spatial dispersion of bluetongue virus, a virus that is also transmitted by Culicoides midges, in 2008 in Switzerland, the spread of SBV occurred from the western to the eastern part of the country. The dispersed incursion of SBV took place in the western part of Switzerland and the virus spread rapidly to the remaining territory. This spatial pattern is consistent with the hypothesis that transmission by Culicoides midges was the main way of spreading.

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.

Experimental Schmallenberg virus infection of pigs

Schmallenberg virus (SBV) is a newly emerged virus responsible for an acute non-specific syndrome in adult cattle including high fever, decrease in milk production and severe diarrhea. It also causes reproductive problems in cattle, sheep and goat including abortions, stillbirths and malformations. The role of pigs in the epidemiology of SBV has not yet been evaluated while this could be interesting seen their suggested role in the epidemiology of the closely related Akabane virus. To address this issue, four 12 week old seronegative piglets were subcutaneously infected with 1 ml of SBV infectious serum (FLI) and kept into contact with four non-infected piglets to examine direct virus transmission. Throughout the experiment blood, swabs and feces samples were collected and upon euthanasia at 28 dpi different organs (cerebrum, cerebellum, brain stem, lung, liver, iliac lymph nodes, kidney and spleen) were sampled. No clinical impact was observed and all collected samples tested negative for SBV in rRT-PCR. Despite the absence of viremia and virus transmission, low and short lasting amounts of neutralizing antibodies were found in 2 out of 4 infected piglets. The limited impact of SBV infection in pigs was further supported by the absence of neutralizing anti-SBV antibodies in field collected sera from indoor housed domestic pigs (n=106). In conclusion, SBV infection of pigs can induce seroconversion but is ineffective in terms of virus replication and transmission indicating that pigs have no obvious role in the SBV epidemiology.

Schmallenberg virus circulation in culicoides in Belgium in 2012: field validation of a real time RT-PCR approach to assess virus replication and dissemination in midges

Indigenous Culicoides biting midges are suggested to be putative vectors for the recently emerged Schmallenberg virus (SBV) based on SBV RNA detection in field-caught midges. Furthermore, SBV replication and dissemination has been evidenced in C. sonorensis under laboratory conditions. After SBV had been detected in Culicoides biting midges from Belgium in August 2011, it spread all over the country by the end of 2011, as evidenced by very high between-herd seroprevalence rates in sheep and cattle. This study investigated if a renewed SBV circulation in midges occurred in 2012 in the context of high seroprevalence in the animal host population and evaluated if a recently proposed realtime RT-PCR approach that is meant to allow assessing the vector competence of Culicoides for SBV and bluetongue virus under laboratory conditions was applicable to field-caught midges. Therefore midges caught with 12 OVI traps in four different regions in Belgium between May and November 2012, were morphologically identified, age graded, pooled and tested for the presence of SBV RNA by realtime RT-PCR. The results demonstrate that although no SBV could be detected in nulliparous midges caught in May 2012, a renewed but short lived circulation of SBV in parous midges belonging to the subgenus Avaritia occured in August 2012 at all four regions. The infection prevalence reached up to 2.86% in the south of Belgium, the region where a lower seroprevalence was found at the end of 2011 than in the rest of the country. Furthermore, a frequency analysis of the Ct values obtained for 31 SBV-S segment positive pools of Avaritia midges showed a clear bimodal distribution with peaks of Ct values between 21–24 and 33–36. This closely resembles the laboratory results obtained for SBV infection of C. sonorensis and implicates indigenous midges belonging to the subgenus Avaritia as competent vectors for SBV.

Evaluating the protective efficacy of a trivalent vaccine containing Akabane virus, Aino virus and Chuzan virus against Schmallenberg virus infection

Schmallenberg virus (SBV), an arthropod borne pathogen, spread rapidly throughout the majority of Europe since 2011. It can cause a febrile disease, milk drop, diarrhea, and fetal malformation in ruminants. SBV, a member of the Simbu serogroup within the genus Orthobunyavirus, is closely related to Akabane virus (AKAV) and Aino virus (AINOV) among others. In the present study, 4 Holstein-Friesian calves were immunized twice four weeks apart with a multivalent, inactivated vaccine against AKAV and AINOV. Another 4 calves were kept as unvaccinated controls. All animals were clinically, serologically and virologically examined before and after challenge infection with SBV. AKAV- and AINOV-specific neutralizing antibodies were detected one week before challenge infection, while SBV-specific antibodies were detectable only thereafter. SBV genome was detected in all vaccinated animals and 3 out of 4 controls in serum samples taken after challenge infection. In conclusion, the investigated vaccine was not able to prevent an SBV-infection. Thus, vaccines for other related Simbu serogroup viruses can not substitute SBV-specific vaccines as an instrument for disease control.

Emerging animal viruses: real threats or simple bystanders?

The list of animal viruses has been frequently added of new members raising permanent concerns to virologists and veterinarians. The pathogenic potential and association with disease have been clearly demonstrated for some, but not for all of these emerging viruses. This review describes recent discoveries of animal viruses and their potential relevance for veterinary practice. Dogs were considered refractory to influenza viruses until 2004, when an influenza A virus subtype H3N8 was transmitted from horses and produced severe respiratory disease in racing greyhounds in Florida/USA. The novel virus, named canine influenza virus (CIV), is considered now a separate virus lineage and has spread among urban canine population in the USA. A new pestivirus (Flaviviridae), tentatively called HoBi-like pestivirus, was identified in 2004 in commercial fetal bovine serum from Brazil. Hobi-like viruses are genetically and antigenically related to bovine viral diarrhea virus (BVDV) and induce similar clinical manifestations. These novel viruses seem to be widespread in Brazilian herds and have also been detected in Southeast Asia and Europe. In 2011, a novel mosquito-borne orthobunyavirus, named Schmallenberg virus (SBV), was associated with fever, drop in milk production, abortion and newborn malformation in cattle and sheep in Germany. Subsequently, the virus disseminated over several European countries and currently represents a real treat for animal health. The origin of SBV is still a matter of debate but it may be a reassortant from previous known bunyaviruses Shamonda and Satuperi. Hepatitis E virus (HEV, family Hepeviridae) is a long known agent of human acute hepatitis and in 1997 was first identified in pigs. Current data indicates that swine HEV is spread worldwide, mainly associated with subclinical infection. Two of the four HEV genotypes are zoonotic and may be transmitted between swine and human by contaminated water and undercooked pork meat. The current distribution and impact of HEV infection in swine production are largely unknown. Avian gyrovirus type 2 (AGV2) is a newly described Gyrovirus, family Circoviridae, which was unexpectedly found in sera of poultry suspected to be infected with chicken anemia virus (CAV). AGV2 is closely related to CAV but displays sufficient genomic differences to be classified as a distinct species. AGV2 seems to be distributed in Brazil and also in other countries but its pathogenic role for chickens is still under investigation. Finally, the long time and intensive search for animal relatives of human hepatitis C virus (HCV) has led to the identification of novel hepaciviruses in dogs (canine hepacivirus [CHV]), horses (non-primate hepaciviruses [NPHV] or Theiler's disease associated virus [TDAV]) and rodents. For these, a clear and definitive association with disease is still lacking and only time and investigation will tell whether they are real disease agents or simple spectators.