Detection of a fourth orbivirus non-structural protein

Characterising Non-Structural Protein NS4 of African Horse Sickness Virus

African horse sickness is a serious equid disease caused by the orbivirus African horse sickness virus (AHSV). The virus has ten double-stranded RNA genome segments encoding seven structural and three non-structural proteins. Recently, an additional protein was predicted to be encoded by genome segment 9 (Seg-9), which also encodes VP6, of most orbiviruses. This has since been confirmed in bluetongue virus and Great Island virus, and the non-structural protein was named NS4. In this study, in silico analysis of AHSV Seg-9 sequences revealed the existence of two main types of AHSV NS4, designated NS4-I and NS4-II, with different lengths and amino acid sequences. The AHSV NS4 coding sequences were in the +1 reading frame relative to that of VP6. Both types of AHSV NS4 were expressed in cultured mammalian cells, with sizes close to the predicted 17–20 kDa. Fluorescence microscopy of these cells revealed a dual cytoplasmic and nuclear, but not nucleolar, distribution that was very similar for NS4-I and NS4-II. Immunohistochemistry on heart, spleen, and lung tissues from AHSV-infected horses showed that NS4 occurs in microvascular endothelial cells and mononuclear phagocytes in all of these tissues, localising to the both the cytoplasm and the nucleus. Interestingly, NS4 was also detected in stellate-shaped dendritic macrophage-like cells with long cytoplasmic processes in the red pulp of the spleen. Finally, nucleic acid protection assays using bacterially expressed recombinant AHSV NS4 showed that both types of AHSV NS4 bind dsDNA, but not dsRNA. Further studies will be required to determine the exact function of AHSV NS4 during viral replication.

Genome Sequence of Bluetongue Virus Type 2 from India: Evidence for Reassortment between Outer Capsid Protein Genes

Southern Indian isolate IND1994/01 of bluetongue virus serotype 2 (BTV-2), from the Orbivirus Reference Collection at the Pirbright Institute (http://www.reoviridae.org/dsRNA_virus_proteins/ReoID/btv-2.htm#IND1994/01), was sequenced. Its genome segment 6 (Seg-6) [encoding VP5(OCP2)] is identical to that of the Indian BTV-1 isolate (IND2003/05), while Seg-5 and Seg-9 are closely related to isolates from South Africa and the United States, respectively.

Genetic characterization of epizootic hemorrhagic disease virus strains isolated from cattle in Israel

Epizootic hemorrhagic disease virus (EHDV), a member of the genus Orbivirus not reported previously in Israel, was isolated from Israeli cattle during a 'bluetongue-like' disease outbreak in 2006. To ascertain the origin of this new virus, three isolates from the outbreak were fully sequenced and compared with available sequences. Whilst the L2 gene segment clustered with the Australian EHDV serotype 7 (EHDV-7) reference strain, most of the other segments were clustered with EHDV isolates of African/Middle East origin, specifically Bahrain, Nigeria and South Africa. The M6 gene had genetic relatedness to the Australian/Asian strains, but with the limited data available the significance of this relationship is unclear. Only one EHDV-7 L2 sequence was available, and as this gene encodes the serotype-specific epitope, the relationship of these EHDV-7 L2 genes to an Australian EHDV-7 reflects the serotype association, not necessarily the origin. The genetic data indicated that the strains affecting Israel in 2006 may have been related to similar outbreaks that occurred in North Africa in the same year. This finding also supports the hypothesis that EHDV entered Israel during 2006 and was not present there before this outbreak.

FRESCo: finding regions of excess synonymous constraint in diverse viruses

Background

The increasing availability of sequence data for many viruses provides power to detect regions under unusual evolutionary constraint at a high resolution. One approach leverages the synonymous substitution rate as a signature to pinpoint genic regions encoding overlapping or embedded functional elements. Protein-coding regions in viral genomes often contain overlapping RNA structural elements, reading frames, regulatory elements, microRNAs, and packaging signals. Synonymous substitutions in these regions would be selectively disfavored and thus these regions are characterized by excess synonymous constraint. Codon choice can also modulate transcriptional efficiency, translational accuracy, and protein folding.

Results

We developed a phylogenetic codon model-based framework, FRESCo, designed to find regions of excess synonymous constraint in short, deep alignments, such as individual viral genes across many sequenced isolates. We demonstrated the high specificity of our approach on simulated data and applied our framework to the protein-coding regions of approximately 30 distinct species of viruses with diverse genome architectures.

Conclusions

FRESCo recovers known multifunctional regions in well-characterized viruses such as hepatitis B virus, poliovirus, and West Nile virus, often at a single-codon resolution, and predicts many novel functional elements overlapping viral genes, including in Lassa and Ebola viruses. In a number of viruses, the synonymously constrained regions that we identified also display conserved, stable predicted RNA structures, including putative novel elements in multiple viral species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0603-7) contains supplementary material, which is available to authorized users.

Application of bluetongue Disabled Infectious Single Animal (DISA) vaccine for different serotypes by VP2 exchange or incorporation of chimeric VP2

Bluetongue is a disease of ruminants caused by the bluetongue virus (BTV). Bluetongue outbreaks can be controlled by vaccination, however, currently available vaccines have several drawbacks. Further, there are at least 26 BTV serotypes, with low cross protection. A next-generation vaccine based on live-attenuated BTV without expression of non-structural proteins NS3/NS3a, named Disabled Infectious Single Animal (DISA) vaccine, was recently developed for serotype 8 by exchange of the serotype determining outer capsid protein VP2. DISA vaccines are replicating vaccines but do not cause detectable viremia, and induce serotype specific protection. Here, we exchanged VP2 of laboratory strain BTV1 for VP2 of European serotypes 2, 4, 8 and 9 using reverse genetics, without observing large effects on virus growth. Exchange of VP2 from serotype 16 and 25 was however not possible. Therefore, chimeric VP2 proteins of BTV1 containing possible immunogenic regions of these serotypes were studied. BTV1, expressing 1/16 chimeric VP2 proteins was functional in virus replication in vitro and contained neutralizing epitopes of both serotype 1 and 16. For serotype 25 this approach failed. We combined VP2 exchange with the NS3/NS3a negative phenotype in BTV1 as previously described for serotype 8 DISA vaccine. DISA vaccine with 1/16 chimeric VP2 containing amino acid region 249-398 of serotype 16 raised antibodies in sheep neutralizing both BTV1 and BTV16. This suggests that DISA vaccine could be protective for both parental serotypes present in chimeric VP2. We here demonstrate the application of the BT DISA vaccine platform for several serotypes and further extend the application for serotypes that are unsuccessful in single VP2 exchange.

VP2-serotyped live-attenuated bluetongue virus without NS3/NS3a expression provides serotype-specific protection and enables DIVA

Bluetongue virus (BTV) causes Bluetongue in ruminants and is transmitted by Culicoides biting midges. Vaccination is the most effective measure to control vector borne diseases; however, there are 26 known BTV serotypes showing little cross protection. The BTV serotype is mainly determined by genome segment 2 encoding the VP2 protein. Currently, inactivated and live-attenuated Bluetongue vaccines are available for a limited number of serotypes, but each of these have their specific disadvantages, including the inability to differentiate infected from vaccinated animals (DIVA). BTV non-structural proteins NS3 and NS3a are not essential for virus replication in vitro, but are important for cytopathogenic effect in mammalian cells and for virus release from insect cells in vitro. Recently, we have shown that virulent BTV8 without NS3/NS3a is non-virulent and viremia in sheep is strongly reduced, whereas local in vivo replication leads to seroconversion. Live-attenuated BTV6 without NS3/NS3a expression protected sheep against BTV challenge. Altogether, NS3/NS3a knockout BTV6 is a promising vaccine candidate and has been named Disabled Infectious Single Animal (DISA) vaccine. Here, we show serotype-specific protection in sheep by DISA vaccine in which only genome segment 2 of serotype 8 was exchanged. Similarly, DISA vaccines against other serotypes could be developed, by exchange of only segment 2, and could therefore safely be combined in multi-serotype cocktail vaccines with respect to reassortment between vaccine viruses. Additionally, NS3 antibody responses are raised after natural BTV infection and NS3-based ELISAs are therefore appropriate tools for DIVA testing accompanying the DISA vaccine. To enable DIVA, we developed an experimental NS3 ELISA. Indeed, vaccinated sheep remained negative for NS3 antibodies, whereas seroconversion for NS3 antibodies was associated with viremia after heterologous BTV challenge.

Full genome characterization of the culicoides-borne marsupial orbiviruses: Wallal virus, Mudjinbarry virus and Warrego viruses

Viruses belonging to the species Wallal virus and Warrego virus of the genus Orbivirus were identified as causative agents of blindness in marsupials in Australia during 1994/5. Recent comparisons of nucleotide (nt) and amino acid (aa) sequences have provided a basis for the grouping and classification of orbivirus isolates. However, full-genome sequence data are not available for representatives of all Orbivirus species. We report full-genome sequence data for three additional orbiviruses: Wallal virus (WALV); Mudjinabarry virus (MUDV) and Warrego virus (WARV). Comparisons of conserved polymerase (Pol), sub-core-shell 'T2' and core-surface 'T13' proteins show that these viruses group with other Culicoides borne orbiviruses, clustering with Eubenangee virus (EUBV), another orbivirus infecting marsupials. WARV shares <70% aa identity in all three conserved proteins (Pol, T2 and T13) with other orbiviruses, consistent with its classification within a distinct Orbivirus species. Although WALV and MUDV share <72.86%/67.93% aa/nt identity with other orbiviruses in Pol, T2 and T13, they share >99%/90% aa/nt identities with each other (consistent with membership of the same virus species - Wallal virus). However, WALV and MUDV share <68% aa identity in their larger outer capsid protein VP2(OC1), consistent with membership of different serotypes within the species - WALV-1 and WALV-2 respectively.

Evolution of bluetongue virus serotype 1 in northern Australia over 30 years

Bluetongue virus serotype 1 (BTV 1) was first isolated in Australia from cattle blood collected in 1979 at Beatrice Hill Farm (BHF), Northern Territory (NT). From long-term surveillance programs (1977 to 2011), 2,487 isolations of 10 BTV serotypes were made. The most frequently isolated serotype was BTV 1 (41%, 1,019) followed by BTV 16 (17.5%, 436) and BTV 20 (14%, 348). In 3 years, no BTVs were isolated, and in 12 years, no BTV 1 was isolated. Seventeen BTV 1 isolates were sequenced and analyzed in comparison with 10 Australian prototype serotypes. BTV 1 showed an episodic pattern of evolutionary change characterized by four distinct periods. Each period consisted primarily of slow genetic drift which was punctuated from time to time by genetic shifts generated by segment reassortment and the introduction of new genome segments. Evidence was found for coevolution of BTV genome segments. Evolutionary dynamics and selection pressure estimates showed strong temporal and clock-like molecular evolutionary dynamics of six Australian BTV genome segments. Bayesian coalescent estimates of mean substitution rates clustered in the range of 3.5 × 10(-4) to 5.3 × 10(-4) substitutions per site per year. All BTV genome segments evolved under strong purifying (negative) selection, with only three sites identified as under pervasive diversifying (positive) selection. The obligate replication in alternate hosts (insect vector and vertebrate hosts) imposed strong evolutionary constraints. The dominant mechanism generating genetic diversity of BTV 1 at BHF was through the introduction of new viruses and reassortment of genome segments with existing viruses.

IMPORTANCE

Bluetongue virus (BTV) is the causative agent of bluetongue disease in ruminants. It is a disease of concern globally and is transmitted by biting midges (Culicoides species). Analysis of the evolutionary and selection pressures on BTV 1 at a single surveillance site in northern Australia showed strong temporal and clock-like dynamics. Obligate replication in alternate hosts of insect and vertebrate imposed strong evolutionary constraints, with all BTV genome segments evolving under strong purifying (negative) selection. Generation of genetic diversity of BTV 1 in northern Australia is through genome segment reassortment and the introduction of new serotypes.

Bluetongue virus without NS3/NS3a expression is not virulent and protects against virulent bluetongue virus challenge

Bluetongue is a disease in ruminants caused by the bluetongue virus (BTV), and is spread by Culicoides biting midges. Bluetongue outbreaks cause huge economic losses and death in sheep in several parts of the world. The most effective measure to control BTV is vaccination. However, both commercially available vaccines and recently developed vaccine candidates have several shortcomings. Therefore, we generated and tested next-generation vaccines for bluetongue based on the backbone of a laboratory-adapted strain of BTV-1, avirulent BTV-6 or virulent BTV-8. All vaccine candidates were serotyped with VP2 of BTV-8 and did not express NS3/NS3a non-structural proteins, due to induced deletions in the NS3/NS3a ORF. Sheep were vaccinated once with one of these vaccine candidates and were challenged with virulent BTV-8 3 weeks after vaccination. The NS3/NS3a knockout mutation caused complete avirulence for all three BTV backbones, including for virulent BTV-8, indicating that safety is associated with the NS3/NS3a knockout phenotype. Viraemia of vaccine virus was not detected using sensitive PCR diagnostics. Apparently, the vaccine viruses replicated only locally, which will minimize spread by the insect vector. In particular, the vaccine based on the BTV-6 backbone protected against disease and prevented viraemia of challenge virus, showing the efficacy of this vaccine candidate. The lack of NS3/NS3a expression potentially enables the differentiation of infected from vaccinated animals, which is important for monitoring virus spread in vaccinated livestock. The disabled infectious single-animal vaccine for bluetongue presented here is very promising and will be the subject of future studies.

Epidemiology of Bluetongue in India

Bluetongue (BT) is an insectborne endemic disease in India. Although infections are observed in domestic and wild ruminants, the clinical disease and mortality are observed only in sheep, especially in the southern states of the country. The difference in disease patterns in different parts of the country could be due to varied climatic conditions, sheep population density and susceptibility of the sheep breeds to BT. Over the five decades after the first report of BT in 1964, most of the known serotypes of bluetongue virus (BTV) have been reported from India either by virus isolation or by detection of serotype-specific antibodies. There have been no structured longitudinal studies to identify the circulating serotypes throughout the country. At least ten serotypes were isolated between 1967 and 2000 (BTV-1-4, 6, 9, 16-18, 23). Since 2001, the All-India Network Programme on Bluetongue and other laboratories have isolated eight different serotypes (BTV-1-3, 9, 10, 12, 16, 21). Genetic analysis of these viruses has revealed that some of them vary substantially from reference viruses, and some show high sequence identity with modified live virus vaccines used in different parts of the world. These observations have highlighted the need to develop diagnostic capabilities, especially as BT outbreaks are still declared based on clinical signs. Although virus isolation and serotyping are the gold standards, rapid methods based on the detection of viral nucleic acid may be more suitable for India. The epidemiological investigations also have implications for vaccine design. Although only a handful serotypes may be involved in causing outbreaks every year, the combination of serotypes may change from year to year. For effective control of BT in India, it may be pertinent to introduce sentinel and vector traps systems for identification of the circulating serotypes and to evaluate herd immunity against different serotypes, so that relevant strains can be included in vaccine formulations.

A synthetic biology approach for a vaccine platform against known and newly emerging serotypes of bluetongue virus

Bluetongue is one of the major infectious diseases of ruminants and is caused by bluetongue virus (BTV), an arbovirus existing in nature in at least 26 distinct serotypes. Here, we describe the development of a vaccine platform for BTV. The advent of synthetic biology approaches and the development of reverse genetics systems has allowed the rapid and reliable design and production of pathogen genomes which can be subsequently manipulated for vaccine production. We describe BTV vaccines based on “synthetic” viruses in which the outer core proteins of different BTV serotypes are incorporated into a common tissue-culture-adapted backbone. As a means of validation for this approach, we selected two BTV-8 synthetic reassortants and demonstrated their ability to protect sheep against virulent BTV-8 challenge. In addition to further highlight the possibilities of genome manipulation for vaccine production, we also designed and rescued a synthetic BTV chimera containing a VP2 protein, including regions derived from both BTV-1 and BTV-8. Interestingly, while the parental viruses were neutralized only by homologous antisera, the chimeric proteins could be neutralized by both BTV-1 and BTV-8 antisera. These data suggest that neutralizing epitopes are present in different areas of the BTV VP2 and likely “bivalent” strains eliciting neutralizing antibodies for multiple strains can be obtained.

IMPORTANCE Overall, this vaccine platform can significantly reduce the time taken from the identification of new BTV strains to the development and production of new vaccines, since the viral genomes of these viruses can be entirely synthesized in vitro. In addition, these vaccines can be brought quickly into the market because they alter the approach, but not the final product, of existing commercial products.

VP2, VP7, and NS1 proteins of bluetongue virus targeted in avian reovirus muNS-Mi microspheres elicit a protective immune response in IFNAR(-/-) mice

Vaccination is critical for controlling the spread of bluetongue virus (BTV). The inactivated BTV vaccines that are now being used in Europe are effective in preventing outbreaks of BTV but secondary effects associated to repetitive inoculation of aluminum-containing adjuvants and the need to develop safer, cross-reactive, and more efficacious vaccines with differential diagnostic capability have re-stimulated the interest in developing improved vaccination strategies against BTV. We have engineered a subunit BTV vaccine candidate based on proteins VP2, VP7, and NS1 of BTV-4 incorporated into avian reovirus (ARV) muNS-Mi microspheres (MS-VP2/MS-VP7/MS-NS1). IFNAR(-/-) mice immunized with MS-VP2/MS-VP7/MS-NS1 without adjuvant generated significant levels of neutralizing antibodies specific to BTV-4. In addition, vaccination stimulated specific T cell responses, predominantly CD4+, against the virus. Immunized mice were fully protected against a homologous challenge with a lethal dose of BTV-4 and partially cross-protected against a heterologous challenge with a lethal dose of BTV-1. These results support MS-VP2/MS-VP7/MS-NS1 as a promising subunit vaccine candidate against multiple serotypes of BTV as well as the use of microspheres as an alternative delivery method with potent intrinsic adjuvant activity.

Dual modulation of type I interferon response by bluetongue virus

Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) virus that causes an economically important disease in ruminants. BTV infection is a strong inducer of type I interferon (IFN-I) in multiple cell types. It has been shown recently that BTV and, more specifically, the nonstructural protein NS3 of BTV are able to modulate the IFN-I synthesis pathway. However, nothing is known about the ability of BTV to counteract IFN-I signaling. Here, we investigated the effect of BTV on the IFN-I response pathway and, more particularly, the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. We found that BTV infection triggered the expression of IFN-stimulated genes (ISGs) in A549 cells. However, when BTV-infected cells were stimulated with external IFN-I, we showed that activation of the IFN-stimulated response element (ISRE) promoter and expression of ISGs were inhibited. We found that this inhibition involved two different mechanisms that were dependent on the time of infection. After overnight infection, BTV blocked specifically the phosphorylation and nuclear translocation of STAT1. This inhibition correlated with the redistribution of STAT1 in regions adjacent to the nucleus. At a later time point of infection, BTV was found to interfere with the activation of other key components of the JAK/STAT pathway and to induce the downregulation of JAK1 and TYK2 protein expression. Overall, our study indicates for the first time that BTV is able to interfere with the JAK/STAT pathway to modulate the IFN-I response.

IMPORTANCE

Bluetongue virus (BTV) causes a severe disease in ruminants and has an important impact on the livestock economy in areas of endemicity such as Africa. The emergence of strains, such as serotype 8 in Europe in 2006, can lead to important economic losses due to commercial restrictions and prophylactic measures. It has been known for many years that BTV is a strong inducer of type I interferon (IFN-I) in vitro and in vivo in multiple cell types. However, the ability of BTV to interact with the IFN-I system remains unclear. Here, we report that BTV is able to modulate the IFN-I response by interfering with the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. These findings contribute to knowledge of how BTV infection interferes with the host's innate immune response and becomes pathogenic. This will also be important for the design of efficacious vaccine candidates.

Virus and host factors affecting the clinical outcome of bluetongue virus infection

Bluetongue is a major infectious disease of ruminants caused by bluetongue virus (BTV), an arbovirus transmitted by Culicoides. Here, we assessed virus and host factors influencing the clinical outcome of BTV infection using a single experimental framework. We investigated how mammalian host species, breed, age, BTV serotypes, and strains within a serotype affect the clinical course of bluetongue. Results obtained indicate that in small ruminants, there is a marked difference in the susceptibility to clinical disease induced by BTV at the host species level but less so at the breed level. No major differences in virulence were found between divergent serotypes (BTV-8 and BTV-2). However, we observed striking differences in virulence between closely related strains of the same serotype collected toward the beginning and the end of the European BTV-8 outbreak. As observed previously, differences in disease severity were also observed when animals were infected with either blood from a BTV-infected animal or from the same virus isolated in cell culture. Interestingly, with the exception of two silent mutations, full viral genome sequencing showed identical consensus sequences of the virus before and after cell culture isolation. However, deep sequencing analysis revealed a marked decrease in the genetic diversity of the viral population after passaging in mammalian cells. In contrast, passaging in Culicoides cells increased the overall number of low-frequency variants compared to virus never passaged in cell culture. Thus, Culicoides might be a source of new viral variants, and viral population diversity can be another factor influencing BTV virulence.

IMPORTANCE Bluetongue is one of the major infectious diseases of ruminants. It is caused by an arbovirus known as bluetongue virus (BTV). The clinical outcome of BTV infection is extremely variable. We show that there are clear links between the severity of bluetongue and the mammalian host species infected, while at the breed level differences were less evident. No differences were observed in the virulence of two different BTV serotypes (BTV-8 and BTV-2). In contrast, we show that the European BTV-8 strain isolated at the beginning of the bluetongue outbreak in 2006 was more virulent than a strain isolated toward the end of the outbreak. In addition, we show that there is a link between the variability of the BTV population as a whole and virulence, and our data also suggest that Culicoides cells might function as an “incubator” of viral variants.

Genetic and biological characterization of selected Changuinola viruses (Reoviridae, Orbivirus) from Brazil

The genus Orbivirus of the family Reoviridae comprises 22 virus species including the Changuinola virus (CGLV) serogroup. The complete genome sequences of 13 CGLV serotypes isolated between 1961 and 1988 from distinct geographical areas of the Brazilian Amazon region were obtained. All viral sequences were obtained from single-passaged CGLV strains grown in Vero cells. CGLVs are the only orbiviruses known to be transmitted by phlebotomine sandflies. Ultrastructure and molecular analysis by electron microscopy and gel electrophoresis, respectively, revealed viral particles with typical orbivirus size and morphology, as well as the presence of a segmented genome with 10 segments. Full-length nucleotide sequencing of each of the ten RNA segments of the 13 CGLV serotypes provided basic information regarding the genome organization, encoded proteins and genetic traits. Segment 2 (encoding VP2) of the CGLV is uncommonly larger in comparison to those found in other orbiviruses and shows varying sizes even among different CGLV serotypes. Phylogenetic analysis support previous serological findings, which indicate that CGLV constitutes a separate serogroup within the genus Orbivirus. In addition, six out of 13 analysed CGLV serotypes showed reassortment of their genome segments.

Vesicular stomatitis virus replicon expressing the VP2 outer capsid protein of bluetongue virus serotype 8 induces complete protection of sheep against challenge infection

Bluetongue virus (BTV) is an arthropod-borne pathogen that causes an often fatal, hemorrhagic disease in ruminants. Different BTV serotypes occur throughout many temperate and tropical regions of the world. In 2006, BTV serotype 8 (BTV-8) emerged in Central and Northern Europe for the first time. Although this outbreak was eventually controlled using inactivated virus vaccines, the epidemic caused significant economic losses not only from the disease in livestock but also from trade restrictions. To date, BTV vaccines that allow simple serological discrimination of infected and vaccinated animals (DIVA) have not been approved for use in livestock. In this study, we generated recombinant RNA replicon particles based on single-cycle vesicular stomatitis virus (VSV) vectors. Immunization of sheep with infectious VSV replicon particles expressing the outer capsid VP2 protein of BTV-8 resulted in induction of BTV-8 serotype-specific neutralizing antibodies. After challenge with a virulent BTV-8 strain, the vaccinated animals neither developed signs of disease nor showed viremia. In contrast, immunization of sheep with recombinant VP5 - the second outer capsid protein of BTV - did not confer protection. Discrimination of infected from vaccinated animals was readily achieved using an ELISA for detection of antibodies against the VP7 antigen. These data indicate that VSV replicon particles potentially represent a safe and efficacious vaccine platform with which to control future outbreaks by BTV-8 or other serotypes, especially in previously non-endemic regions where discrimination between vaccinated and infected animals is crucial.

Immunisation with bacterial expressed VP2 and VP5 of bluetongue virus (BTV) protect α/β interferon-receptor knock-out (IFNAR(-/-)) mice from homologous lethal challenge

BTV-4 structural proteins VP2 (as two domains: VP2D1 and VP2D2), VP5 (lacking the first 100 amino acids: VP5Δ1-100) and full-length VP7, expressed in bacteria as soluble glutathione S-transferase (GST) fusion-proteins, were used to immunise Balb/c and α/β interferon receptor knock-out (IFNAR(-/-)) mice. Neutralising antibody (NAbs) titres (expressed as log10 of the reciprocal of the last dilution of mouse serum which reduced plaque number by ≥50%) induced by the VP2 domains ranged from 1.806 to 2.408 in Balb/c and IFNAR(-/-) mice. The immunised IFNAR(-/-) mice challenged with a homologous live BTV-4 survived and failed to develop signs of infection (ocular discharge and apathy). Although subsequent attempts to isolate virus were unsuccessful (possibly reflecting presence of neutralising antibodies), a transient/low level viraemia was detected by real time RT-PCR. In contrast, mice immunised with the two VP2 domains with or without VP5Δ1-100 and VP7, then challenged with the heterologous serotype, BTV-8, all died by day 7 post-infection. We conclude that immunisation with bacterially-expressed VP2 domains can induce strong serotype-specific NAb responses. Bacterial expression could represent a cost effective and risk-free alternative to the use of live or inactivated vaccines, particularly if viruses prove to be difficult to propagate in cell culture (like BTV-25). A vaccine based on bacterially expressed VP2 and VP5 of BTV is also DIVA-compatible.

Evidence for transmission of bluetongue virus serotype 26 through direct contact

The aim of this study was to assess the mechanisms of transmission of bluetongue virus serotype 26 (BTV-26) in goats. A previous study, which investigated the pathogenicity and infection kinetics of BTV-26 in goats, unexpectedly revealed that one control goat may have been infected through a direct contact transmission route. To investigate the transmission mechanisms of BTV-26 in more detail an experimental infection study was carried out in which three goats were infected with BTV-26, three goats were kept uninfected, but were housed in direct contact with the infected goats, and an additional four goats were kept in indirect contact separated from infected goats by metal gates. This barrier allowed the goats to have occasional face-to-face contact in the same airspace, but feeding, watering, sampling and environmental cleaning was carried out separately. The three experimentally infected goats did not show clinical signs of BTV, however high levels of viral RNA were detected and virus was isolated from their blood. At 21 dpi viral RNA was detected in, and virus was isolated from the blood of the three direct contact goats, which also seroconverted. The four indirect barrier contact goats remained uninfected throughout the duration of the experiment. In order to assess replication in a laboratory model species of Culicoides biting midge, more than 300 Culicoides sonorensis were fed a BTV-26 spiked blood meal and incubated for 7 days. The dissemination of BTV-26 in individual C. sonorensis was inferred from the quantity of virus RNA and indicated that none of the insects processed at day 7 possessed transmissible infections. This study shows that BTV-26 is easily transmitted through direct contact transmission between goats, and the strain does not seem to replicate in C. sonorensis midges using standard incubation conditions.

Real time RT-PCR assays for detection and typing of African horse sickness virus

Although African horse sickness (AHS) can cause up to 95% mortality in horses, naïve animals can be protected by vaccination against the homologous AHSV serotype. Genome segment 2 (Seg-2) encodes outer capsid protein VP2, the most variable of the AHSV proteins. VP2 is also a primary target for AHSV specific neutralising antibodies, and consequently determines the identity of the nine AHSV serotypes. In contrast VP1 (the viral polymerase) and VP3 (the sub-core shell protein), encoded by Seg-1 and Seg-3 respectively, are highly conserved, representing virus species/orbivirus-serogroup-specific antigens. We report development and evaluation of real-time RT-PCR assays targeting AHSV Seg-1 or Seg-3, that can detect any AHSV type (virus species/serogroup-specific assays), as well as type-specific assays targeting Seg-2 of the nine AHSV serotypes. These assays were evaluated using isolates of different AHSV serotypes and other closely related orbiviruses, from the ‘Orbivirus Reference Collection’ (ORC) at The Pirbright Institute. The assays were shown to be AHSV virus-species-specific, or type-specific (as designed) and can be used for rapid, sensitive and reliable detection and identification (typing) of AHSV RNA in infected blood, tissue samples, homogenised Culicoides, or tissue culture supernatant. None of the assays amplified cDNAs from closely related heterologous orbiviruses, or from uninfected host animals or cell cultures.

RNA elements in open reading frames of the bluetongue virus genome are essential for virus replication

Members of the Reoviridae family are non-enveloped multi-layered viruses with a double stranded RNA genome consisting of 9 to 12 genome segments. Bluetongue virus is the prototype orbivirus (family Reoviridae, genus Orbivirus), causing disease in ruminants, and is spread by Culicoides biting midges. Obviously, several steps in the Reoviridae family replication cycle require virus specific as well as segment specific recognition by viral proteins, but detailed processes in these interactions are still barely understood. Recently, we have shown that expression of NS3 and NS3a proteins encoded by genome segment 10 of bluetongue virus is not essential for virus replication. This gave us the unique opportunity to investigate the role of RNA sequences in the segment 10 open reading frame in virus replication, independent of its protein products. Reverse genetics was used to generate virus mutants with deletions in the open reading frame of segment 10. Although virus with a deletion between both start codons was not viable, deletions throughout the rest of the open reading frame led to the rescue of replicating virus. However, all bluetongue virus deletion mutants without functional protein expression of segment 10 contained inserts of RNA sequences originating from several viral genome segments. Subsequent studies showed that these RNA inserts act as RNA elements, needed for rescue and replication of virus. Functionality of the inserts is orientation-dependent but is independent from the position in segment 10. This study clearly shows that RNA in the open reading frame of Reoviridae members does not only encode proteins, but is also essential for virus replication.

Viral replication kinetics and in vitro cytopathogenicity of parental and reassortant strains of bluetongue virus serotype 1, 6 and 8

Bluetongue virus (BTV), a segmented dsRNA virus, is the causative agent of bluetongue (BT), an economically important viral haemorrhagic disease of ruminants. Bluetongue virus can exchange its genome segments in mammalian or insect cells that have been co-infected with more than one strain of the virus. This process, may potentially give rise to the generation of novel reassortant strains that may differ from parental strains in regards to their phenotypic characteristics. To investigate the potential effects of reassortment on the virus' phenotype, parental as well as reassortant strains of BTV serotype 1, 6, 8, that were derived from attenuated and wild type strains by reverse genetics, were studied in vitro for their virus replication kinetics and cytopathogenicity in mammalian (Vero) cell cultures. The results indicate that genetic reassortment can affect viral replication kinetics, the cytopathogenicity and extent/mechanism of cell death in infected cell cultures. In particular, some reassortants of non-virulent vaccine (BTV-1 and BTV-6) and virulent field origin (BTV-8) demonstrate more pronounced cytopathic effects compared to their parental strains. Some reassortant strains in addition replicated to high titres in vitro despite being composed of genome segments from slow and fast replicating parental strains. The latter result may have implications for the level of viraemia in the mammalian host and subsequent uptake and transmission of reassortant strains (and their genome segments) by Culicoides vectors. Increased rates of CPE induction could further suggest a higher virulence for reassortant strains in vivo. Overall, these findings raise questions in regards to the use of modified-live virus (MLV) vaccines and risk of reassortment in the field. To further address these questions, additional experimental infection studies using insects and/or animal models should be conducted, to determine whether these results have significant implications in vivo.

Vaccination of mice with a modified Vaccinia Ankara (MVA) virus expressing the African horse sickness virus (AHSV) capsid protein VP2 induces virus neutralising antibodies that confer protection against AHSV upon passive immunisation

In previous studies we showed that a recombinant Modified Vaccinia Ankara (MVA) virus expressing the protein VP2 of AHSV serotype 4 (MVA-VP2) induced virus neutralising antibodies in horses and protected interferon alpha receptor gene knock-out mice (IFNAR-/-) against challenge. We continued these studies and determined, in the IFNAR-/- mouse model, whether the antibody responses induced by MVA-VP2 vaccination play a key role in protection against AHSV. Thus, groups of mice were vaccinated with wild type MVA (MVA-wt) or MVA-VP2 and the antisera from these mice were used in a passive immunisation experiment. Donor antisera from (a) MVA-wt; (b) MVA-VP2 vaccinated; or (c) MVA-VP2 vaccinated and AHSV infected mice, were transferred to AHSV non-immune recipient mice. The recipients were challenged with virulent AHSV together with MVA-VP2 vaccinated and MVA-wt vaccinated control animals and the levels of protection against AHSV-4 were compared between all these groups. The results showed that following AHSV challenge, mice that were passively immunised with MVA-VP2 vaccinated antisera were highly protected against AHSV disease and had lower levels of viraemia than recipients of MVA-wt antisera. Our study indicates that MVA-VP2 vaccination induces a highly protective humoral immune response against AHSV.

Full-genome characterisation of Orungo, Lebombo and Changuinola viruses provides evidence for co-evolution of orbiviruses with their arthropod vectors

The complete genomes of Orungo virus (ORUV), Lebombo virus (LEBV) and Changuinola virus (CGLV) were sequenced, confirming that they each encode 11 distinct proteins (VP1-VP7 and NS1-NS4). Phylogenetic analyses of cell-attachment protein 'outer-capsid protein 1' (OC1), show that orbiviruses fall into three large groups, identified as: VP2(OC1), in which OC1 is the 2nd largest protein, including the Culicoides transmitted orbiviruses; VP3(OC1), which includes the mosquito transmitted orbiviruses; and VP4(OC1) which includes the tick transmitted viruses. Differences in the size of OC1 between these groups, places the T2 'subcore-shell protein' as the third largest protein 'VP3(T2)' in the first of these groups, but the second largest protein 'VP3(T2)' in the other two groups. ORUV, LEBV and CGLV all group with the Culicoides-borne VP2(OC1)/VP3(T2) viruses. The G+C content of the ORUV, LEBV and CGLV genomes is also similar to that of the Culicoides-borne, rather than the mosquito-borne, or tick borne orbiviruses. These data suggest that ORUV and LEBV are Culicoides- rather than mosquito-borne. Multiple isolations of CGLV from sand flies suggest that they are its primary vector. OC1 of the insect-borne orbiviruses is approximately twice the size of the equivalent protein of the tick borne viruses. Together with internal sequence similarities, this suggests its origin by duplication (concatermerisation) of a smaller OC1 from an ancestral tick-borne orbivirus. Phylogenetic comparisons showing linear relationships between the dates of evolutionary-separation of their vector species, and genetic-distances between tick-, mosquito- or Culicoides-borne virus-groups, provide evidence for co-evolution of the orbiviruses with their arthropod vectors.

Bluetongue virus nonstructural protein NS3/NS3a is not essential for virus replication

Orbiviruses form the largest genus of the family Reoviridae consisting of at least 23 different virus species. One of these is the bluetongue virus (BTV) and causes severe hemorrhagic disease in ruminants, and is transmitted by bites of Culicoides midges. BTV is a non-enveloped virus which is released from infected cells by cell lysis and/or a unique budding process induced by nonstructural protein NS3/NS3a encoded by genome segment 10 (Seg-10). Presence of both NS3 and NS3a is highly conserved in Culicoides borne orbiviruses which is suggesting an essential role in virus replication. We used reverse genetics to generate BTV mutants to study the function of NS3/NS3a in virus replication. Initially, BTV with small insertions in Seg-10 showed no CPE but after several passages these BTV mutants reverted to CPE phenotype comparable to wtBTV, and NS3/NS3a expression returned by repair of the ORF. These results show that there is a strong selection for functional NS3/NS3a. To abolish NS3 and/or NS3a expression, Seg-10 with one or two mutated start codons (mutAUG1, mutAUG2 and mutAUG1+2) were used to generate BTV mutants. Surprisingly, all three BTV mutants were generated and the respective AUG^Met→GCC^Ala mutations were maintained. The lack of expression of NS3, NS3a, or both proteins was confirmed by westernblot analysis and immunostaining of infected cells with NS3/NS3a Mabs. Growth of mutAUG1 and mutAUG1+2 virus in BSR cells was retarded in both insect and mammalian cells, and particularly virus release from insect cells was strongly reduced. Our findings now enable research on the role of RNA sequences of Seg-10 independent of known gene products, and on the function of NS3/NS3a proteins in both types of cells as well as in the host and insect vector.

The molecular biology of Bluetongue virus replication

The members of Orbivirus genus within the Reoviridae family are arthropod-borne viruses which are responsible for high morbidity and mortality in ruminants. Bluetongue virus (BTV) which causes disease in livestock (sheep, goat, cattle) has been in the forefront of molecular studies for the last three decades and now represents the best understood orbivirus at a molecular and structural level. The complex nature of the virion structure has been well characterised at high resolution along with the definition of the virus encoded enzymes required for RNA replication; the ordered assembly of the capsid shell as well as the protein and genome sequestration required for it; and the role of host proteins in virus entry and virus release. More recent developments of Reverse Genetics and Cell-Free Assembly systems have allowed integration of the accumulated structural and molecular knowledge to be tested at meticulous level, yielding higher insight into basic molecular virology, from which the rational design of safe efficacious vaccines has been possible. This article is centred on the molecular dissection of BTV with a view to understanding the role of each protein in the virus replication cycle. These areas are important in themselves for BTV replication but they also indicate the pathways that related viruses, which includes viruses that are pathogenic to man and animals, might also use providing an informed starting point for intervention or prevention.

Full Genome Sequence of a Western Reference Strain of Bluetongue Virus Serotype 16 from Nigeria

The genome of NIG1982/10, a Nigerian bluetongue virus serotype 16 (BTV-16) strain, was sequenced (19,193 bp). Comparisons to BTV strains from other areas of the world show that all 10 genome segments of NIG1982/10 are derived from a western lineage (w), indicating that it represents a suitable reference strain of BTV-16w.

Bluetongue virus infection induces aberrant mitosis in mammalian cells

Background

Bluetongue virus (BTV) is an arbovirus that is responsible for ‘bluetongue’, an economically important disease of livestock. Although BTV is well characterised at the protein level, less is known regarding its interaction with host cells. During studies of virus inclusion body formation we observed what appeared to be a large proportion of cells in mitosis. Although the modulation of the cell cycle is well established for many viruses, this was a novel observation for BTV. We therefore undertook a study to reveal in more depth the impact of BTV upon cell division.

Methods

We used a confocal microscopy approach to investigate the localisation of BTV proteins in a cellular context with their respective position relative to cellular proteins. In addition, to quantitatively assess the frequency of aberrant mitosis induction by the viral non-structural protein (NS) 2 we utilised live cell imaging to monitor HeLa-mCherry tubulin cells transfected with a plasmid expressing NS2.

Results

Our data showed that these ‘aberrant mitoses’ can be induced in multiple cell types and by different strains of BTV. Further study confirmed multiplication of the centrosomes, each resulting in a separate mitotic spindle during mitosis. Interestingly, the BTV NS1 protein was strongly localised to the centrosomal regions. In a separate, yet related observation, the BTV NS2 protein was co-localised with the condensed chromosomes to a region suggestive of the kinetochore. Live cell imaging revealed that expression of an EGFP-NS2 fusion protein in HeLa-mCherry tubulin cells also results in mitotic defects.

Conclusions

We hypothesise that NS2 is a microtubule cargo protein that may inadvertently disrupt the interaction of microtubule tips with the kinetochores during mitosis. Furthermore, the BTV NS1 protein was distinctly localised to a region encompassing the centrosome and may therefore be, at least in part, responsible for the disruption of the centrosome as observed in BTV infected mammalian cells.

Development of a real time polymerase chain reaction assay for equine encephalosis virus

Equine encephalosis virus (EEV) is the cause of equine encephalosis. The disease is similar to mild forms of African horse sickness (AHS) and the two diseases are easily confused. Laboratory identification and serotyping of EEV is based on viral isolation in BHK-21 cells and a viral plaque inhibition neutralisation test. These procedures are time-consuming and therefore a more rapid diagnostic assay for EEV that can distinguish EEV from African horse sickness virus (AHSV) infections was developed. The S7 (VP7) gene from 38 EEV isolates representing all seven serotypes was amplified and sequenced. A conserved region at the 5' end of the gene was identified and used to design group-specific EEV primers and a TaqMan(®) MGB™ hydrolysis probe. The efficiency of the EEV real-time RT-PCR assay was 81%. The assay was specific, as it did not detect any of the nine serotypes of AHSV, nor 24 serotypes of bluetongue virus (BTV) and sensitive, with a 95% limit of detection of 10(2.9) TCID50/ml blood (95% confidence interval: 10(2.7) to 10(3.3)). The real-time format was selected because of its convenience, sensitivity and ability to produce results rapidly.

Epizootic hemorrhagic disease virus induces and benefits from cell stress, autophagy, and apoptosis

The mode and timing of virally induced cell death hold the potential of regulating viral yield, viral transmission, and the severity of virally induced disease. Orbiviruses such as the epizootic hemorrhagic disease virus (EHDV) are nonenveloped and cytolytic. To date, the death of cells infected with EHDV, the signal transduction pathways involved in this process, and the consequence of their inhibition have yet to be characterized. Here, we report that the Ibaraki strain of EHDV2 (EHDV2-IBA) induces apoptosis, autophagy, a decrease in cellular protein synthesis, the activation of c-Jun N-terminal kinase (JNK), and the phosphorylation of the JNK substrate c-Jun. The production of infectious virions decreased upon inhibition of apoptosis with the pan-caspase inhibitor Q-VD-OPH (quinolyl-valyl-O-methylaspartyl-[-2,6-difluorophenoxy]-methyl ketone), upon inhibition of autophagy with 3-methyladenine or via the knockout of the autophagy regulator Atg5, or upon treatment of infected cells with the JNK inhibitor SP600125 or the cyclin-dependent kinase (CDK) inhibitor roscovitine, which also inhibited c-Jun phosphorylation. Moreover, Q-VD-OPH, SP600125, and roscovitine partially reduced EHDV2-IBA-induced cell death, and roscovitine diminished the induction of autophagy by EHDV2-IBA. Taken together, our results imply that EHDV induces and benefits from the activation of signaling pathways involved in cell stress and death.

Full genome sequencing of Corriparta virus, identifies California mosquito pool virus as a member of the Corriparta virus species

The species Corriparta virus (CORV), within the genus Orbivirus, family Reoviridae, currently contains six virus strains: corriparta virus MRM1 (CORV-MRM1); CS0109; V654; V370; Acado virus and Jacareacanga virus. However, lack of neutralization assays, or reference genome sequence data has prevented further analysis of their intra-serogroup/species relationships and identification of individual serotypes. We report whole-genome sequence data for CORV-MRM1, which was isolated in 1960 in Australia. Comparisons of the conserved, polymerase (VP1), sub-core-shell 'T2' and core-surface 'T13' proteins encoded by genome segments 1, 2 and 8 (Seg-1, Seg-2 and Seg-8) respectively, show that this virus groups with the other mosquito borne orbiviruses. However, highest levels of nt/aa sequence identity (75.9%/91.6% in Seg-2/T2: 77.6%/91.7% in Seg-8/T13, respectively) were detected between CORV-MRM1 and California mosquito pool virus (CMPV), an orbivirus isolated in the USA in 1974, showing that they belong to the same virus species. The data presented here identify CMPV as a member of the Corriparta virus species and will facilitate identification of additional CORV isolates, diagnostic assay design and epidemiological studies.

Ns1 is a key protein in the vaccine composition to protect Ifnar(-/-) mice against infection with multiple serotypes of African horse sickness virus

African horse sickness virus (AHSV) belongs to the genus Orbivirus. We have now engineered naked DNAs and recombinant modified vaccinia virus Ankara (rMVA) expressing VP2 and NS1 proteins from AHSV-4. IFNAR((-/-)) mice inoculated with DNA/rMVA-VP2,-NS1 from AHSV-4 in an heterologous prime-boost vaccination strategy generated significant levels of neutralizing antibodies specific of AHSV-4. In addition, vaccination stimulated specific T cell responses against the virus. The vaccine elicited partial protection against an homologous AHSV-4 infection and induced cross-protection against the heterologous AHSV-9. Similarly, IFNAR((-/-)) mice vaccinated with an homologous prime-boost strategy with rMVA-VP2-NS1 from AHSV-4 developed neutralizing antibodies and protective immunity against AHSV-4. Furthermore, the levels of immunity were very high since none of vaccinated animals presented viraemia when they were challenged against the homologous AHSV-4 and very low levels when they were challenged against the heterologous virus AHSV-9. These data suggest that the immunization with rMVA/rMVA was more efficient in protection against a virulent challenge with AHSV-4 and both strategies, DNA/rMVA and rMVA/rMVA, protected against the infection with AHSV-9. The inclusion of the protein NS1 in the vaccine formulations targeting AHSV generates promising multiserotype vaccines.

Endogenous tick viruses and modulation of tick-borne pathogen growth

Ticks transmit a wide range of viral, bacterial and protozoan pathogens, many of which can establish persistent infections of lifelong duration in the vector tick and in some cases are transmitted transovarially to the next generation. In addition many ixodid and argasid tick cell lines and, by inference the parent ticks from which they were derived, harbor endogenous viruses (ETV) of which almost nothing is known. In general, low level persistent infections with viral pathogens (arboviruses) are not known to have a deleterious effect on tick survival and fitness, suggesting that they can strike a balance with the tick innate immune response. This tolerance of arbovirus infection may be modulated by the permanent presence of ETV in the host cell. In mosquito cells, temporary or permanent silencing of the genes of an endogenous virus by RNA interference can result in changes in replication rate of a co-infecting arbovirus. We propose that tick cell lines offer a useful model system for in vitro investigation of the modulatory effect of ETV on superinfecting pathogen survival and replication in ticks, using the molecular manipulation techniques applied to insect cells.

Full-Genome Sequence of Bluetongue Virus Serotype 1 (BTV-1) Strain Y863, the First BTV-1 Isolate of Eastern Origin Found in China

The full-genome sequence of the bluetongue virus serotype 1 (BTV-1) strain Y863, the first BTV-1 isolate of Eastern origin found in China, was determined. The virus was isolated from sheep during a severe outbreak of bluetongue in Shizhong County, Yunnan Province, southwest China, in 1979. The total size of the BTV-1 strain Y863 genome is 19,170 bp. Phylogenetic analyses demonstrate that it belongs to the major “Eastern” BTV topotype. The sequence information provided here will help in understanding the geographical origin and spread of this Chinese isolate of BTV-1, as well as aid in its comparison with global isolates of BTV-1 from sheep, cattle, and other host species origins.

Deep sequencing as a method of typing bluetongue virus isolates

Bluetongue (BT) is an economically important endemic disease of livestock in tropics and subtropics. In addition, its recent spread to temperate regions like North America and Northern Europe is of serious concern. Rapid serotyping and characterization of BT virus (BTV) is an essential step in the identification of origin of the virus and for controlling the disease. Serotyping of BTV is typically performed by serum neutralization, and of late by nucleotide sequencing. This report describes the near complete genome sequencing and typing of two isolates of BTV using Illumina next generation sequencing platform. Two of the BTV RNAs were multiplexed with ten other unknown samples. Viral RNA was isolated and fragmented, reverse transcribed, the cDNA ends were repaired and ligated with a multiplex oligo. The genome library was amplified using primers complementary to the ligated oligo and subjected to single and paired end sequencing. The raw reads were assembled using a de novo method and reference-based assembly was performed based on the contig data. Near complete sequences of all segments of BTV were obtained with more than 20× coverage, and single read sequencing method was sufficient to identify the genotype and serotype of the virus. The two viruses used in this study were typed as BTV-1 and BTV-9E.

NS3 of bluetongue virus interferes with the induction of type I interferon

Upon infection with Bluetongue virus (BTV), an arthropod-borne virus, type I interferon (IFN-I) is produced in vivo and in vitro. IFN-I is essential for the establishment of an antiviral cellular response, and most if not all viruses have elaborated strategies to counteract its action. In this study, we assessed the ability of BTV to interfere with IFN-I synthesis and identified the nonstructural viral protein NS3 as an antagonist of the IFN-I system.

Identification of a linear B-cell epitope within the Bluetongue virus serotype 8 NS2 protein using a phage-displayed random peptide library

The NS2 protein of Bluetongue virus (BTV) is an important non-structural protein and plays important roles in viral replication and assembly. In this study, one monoclonal antibody (mAb), 4D4, was raised against BTV8 NS2. Phage display technology was used and identified the consensus binding motif SNYD recognized by mAb 4D4. To define the minimal region required for antibody binding, a panel of synthetic peptides encompassing SNYD derived from the BTV8 NS2 was then used to more specifically define the 4D4 epitope as (149)RSNYDV(154). Furthermore, amino acid sequence alignments of different BTV serotypes and other orbiviruses suggested that this epitope is highly conserved among the BTV serotypes. The mAb reagent generated in this study may be applied to the development of BTV diagnosis and surveillance programs and the epitope defined here can lead to important insights into how BTV might interact with the sheep's immune system.

Protection of IFNAR (-/-) mice against bluetongue virus serotype 8, by heterologous (DNA/rMVA) and homologous (rMVA/rMVA) vaccination, expressing outer-capsid protein VP2

The protective efficacy of recombinant vaccines expressing serotype 8 bluetongue virus (BTV-8) capsid proteins was tested in a mouse model. The recombinant vaccines comprised plasmid DNA or Modified Vaccinia Ankara viruses encoding BTV VP2, VP5 or VP7 proteins. These constructs were administered alone or in combination using either a homologous prime boost vaccination regime (rMVA/rMVA) or a heterologous vaccination regime (DNA/rMVA). The DNA/rMVA or rMVA/rMVA prime-boost were administered at a three week interval and all of the animals that received VP2 generated neutralising antibodies. The vaccinated and non-vaccinated-control mice were subsequently challenged with a lethal dose of BTV-8. Mice vaccinated with VP7 alone were not protected. However, mice vaccinated with DNA/rMVA or rMVA/rMVA expressing VP2, VP5 and VP7 or VP2 alone were all protected.

Full genome sequence of bluetongue virus serotype 4 from China

The complete genomic sequence of a bluetongue virus serotype 4 (BTV-4) strain (strain YTS-4), isolated from sentinel cattle in Yunnan Province, China, is reported here. This work is the first to document the complete genomic sequence of a BTV-4 strain from China. The sequence information will help determine the geographic origin of Chinese BTV-4 and provide data to facilitate future analyses of the genetic diversity and phylogenetic relationships of BTV strains.

Reassortment between two serologically unrelated bluetongue virus strains is flexible and can involve any genome segment

Coinfection of a cell by two different strains of a segmented virus can give rise to a "reassortant" with phenotypic characteristics that might differ from those of the parental strains. Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) segmented virus and the cause of bluetongue, a major infectious disease of livestock. BTV exists as at least 26 different serotypes (BTV-1 to BTV-26). Prompted by the isolation of a field reassortant between BTV-1 and BTV-8, we systematically characterized the process of BTV reassortment. Using a reverse genetics approach, our study clearly indicates that any BTV-1 or BTV-8 genome segment can be rescued in the heterologous "backbone." To assess phenotypic variation as a result of reassortment, we examined viral growth kinetics and plaque sizes in in vitro experiments and virulence in an experimental mouse model of bluetongue disease. The monoreassortants generated had phenotypes that were very similar to those of the parental wild-type strains both in vitro and in vivo. Using a forward genetics approach in cells coinfected with BTV-1 and BTV-8, we have shown that reassortants between BTV-1 and BTV-8 are generated very readily. After only four passages in cell culture, we could not detect wild-type BTV-1 or BTV-8 in any of 140 isolated viral plaques. In addition, most of the isolated reassortants contained heterologous VP2 and VP5 structural proteins, while only 17% had homologous VP2 and VP5 proteins. Our study has shown that reassortment in BTV is very flexible, and there is no fundamental barrier to the reassortment of any genome segment. Given the propensity of BTV to reassort, it is increasingly important to have an alternative classification system for orbiviruses.

Complete genome sequence analysis of a reference strain of bluetongue virus serotype 16

The entire genome of the reference strain of bluetongue virus (BTV) serotype 16 (strain RSArrrr/16) was sequenced (a total of 23,518 base pairs). The virus was obtained from the Orbivirus Reference Collection (ORC) at IAH, Pirbright, United Kingdom. The virus strain, which was previously provided by the Onderstepoort Veterinary Research Institute in South Africa, was originally isolated from the Indian subcontinent (Hazara, West Pakistan) in 1960. Previous phylogenetic comparisons show that BTV RNA sequences cluster according to the geographic origins of the virus isolate/lineage, identifying distinct BTV topotypes. Sequence comparisons of segments Seg-1 to Seg-10 show that RSArrrr/16 belongs to the major eastern topotype of BTV (BTV-16e) and can be regarded as a reference strain of BTV-16e for phylogenetic and molecular epidemiology studies. All 10 genome segments of RSArrrr/16 group closely with the vaccine strain of BTV-16 (RSAvvvv/16) that was derived from it, as well as those recently published for a Chinese isolate of BTV-16 (>99% nucleotide identity), suggesting a very recent common ancestry for all three viruses.

Sensing and control of bluetongue virus infection in epithelial cells via RIG-I and MDA5 helicases

Bluetongue virus (BTV), an arthropod-borne member of the Reoviridae family, is a double-stranded RNA virus that causes an economically important livestock disease that has spread across Europe in recent decades. Production of type I interferon (alpha/beta interferon [IFN-α/β]) has been reported in vivo and in vitro upon BTV infection. However, the cellular sensors and signaling pathways involved in this process remain unknown. Here we studied the mechanisms responsible for the production of IFN-β in response to BTV serotype 8. Upon BTV infection of A549 cells, expression of IFN-β and other proinflammatory cytokines was strongly induced at both the protein and mRNA levels. This response appeared to be dependent on virus replication, since exposure to UV-inactivated virus failed to induce IFN-β. We also demonstrated that BTV infection activated the transcription factors IFN regulatory factor 3 and nuclear factor κB. We investigated the role of several pattern recognition receptors in this response and showed that expression of IFN-β was greatly reduced after small-interfering-RNA-mediated knockdown of the RNA helicase encoded by retinoic acid-inducible gene I (RIG-I) or melanoma differentiation-associated gene 5 (MDA5). In contrast, silencing of MyD88, Toll-like receptor 3, or the recently described DexD/H-box helicase DDX1 sensor had no or a weak effect on IFN-β induction, suggesting that the RIG-I-like receptor pathway is specifically engaged for BTV sensing. Moreover, we also showed that overexpression of either RIG-I or MDA5 impaired BTV expression in infected A549 cells. Overall, this indicates that RIG-I and MDA5 can both contribute to the recognition and control of BTV infection.

Bluetongue viruses based on modified-live vaccine serotype 6 with exchanged outer shell proteins confer full protection in sheep against virulent BTV8

Since 1998, Bluetongue virus (BTV)-serotypes 1, 2, 4, 9, and 16 have invaded European countries around the Mediterranean Basin. In 2006, a huge BT outbreak started after incursion of BTV serotype 8 (BTV8) in North-Western Europe. IN 2008, BTV6 and BTV11 were reported in the Netherlands and Germany, and in Belgium, respectively. In addition, Toggenburg orbivirus (TOV) was detected in 2008 in Swiss goats, which was recognized as a new serotype of BTV (BTV25). The (re-)emergency of BTV serotypes needs a rapid response to supply effective vaccines. Reverse genetics has been developed for BTV1 and more recently also for BTV6. This latter strain, BTV6/net08, is closely related to live-attenuated vaccine for serotype 6 as determined by full genome sequencing. Here, we used this strain as backbone and exchanged segment 2 and 6, respectively Seg-2 (VP2) and Seg-6 (VP5), for those of BTV serotype 1 and 8 using reverse genetics. These so-called 'serotyped' vaccine viruses, as mono-serotype and multi-serotype vaccine, were compared for their protective capacity in sheep. In general, all vaccinated animals developed a neutralizing antibody response against their respective serotype. After challenge at three weeks post vaccination with cell-passaged, virulent BTV8/net07 (BTV8/net07/e1/bhkp3) the vaccinated animals showed nearly no clinical reaction. Even more, challenge virus could not be detected, and seroconversion or boostering after challenge was negligible. These data demonstrate that all sheep were protected from a challenge with BTV8/net07, since sheep of the control group showed viremia, seroconversion and clinical signs that are specific for Bluetongue. The high level of cross-protection is discussed.

Bluetongue: a historical and epidemiological perspective with the emphasis on South Africa

Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria, South Africa. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd-immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field.

Bluetongue virus serotype 26: infection kinetics, pathogenesis and possible contact transmission in goats

The aim of this study was to assess the pathogenicity and infection kinetics of Bluetongue virus serotype 26 (BTV-26) in goats. Out of a group of six goats housed in insect free accommodation, five were experimentally infected with BTV-26 and one was kept uninfected as an in-contact control. Samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and a group specific ELISA. The five infected goats did not show clinical signs of BTV, however high levels of viral RNA were detected and virus was isolated from the blood of all 5 goats. Antibodies against BTV were first detected between 7 and 11 dpi in all 5 experimentally infected goats. Interestingly at 21 dpi viral RNA was detected in, and virus was isolated from, the blood of the in-contact control goat, which also seroconverted. These results suggest that BTV-26 replicates to high levels in goats, causing no obvious clinical disease, suggesting that goats may be the natural host for this virus. Preliminary evidence also indicates that BTV-26 may be spread by contact transmission between goats, however a more detailed study is required in order to confirm this observation.

Genome sequence of a reassortant strain of bluetongue virus serotype 23 from western India

The full genome sequence (19,177 bp) of an Indian strain (IND1988/02) of bluetongue virus (BTV) serotype 23 was determined. This virus was isolated from a sheep that had been killed during a severe bluetongue outbreak that occurred in Rahuri, Maharashtra State, western India, in 1988. Phylogenetic analyses of these data demonstrate that most of the genome segments from IND1988/02 belong to the major "eastern" BTV topotype. However, genome segment 5 belongs to the major "western" BTV topotype, demonstrating that IND1988/02 is a reassortant. This may help to explain the increased virulence that was seen during this outbreak in 1988. Genome segment 5 of IND1988/02 shows >99% sequence identity with some other BTV isolates from India (e.g., BTV-3 IND2003/08), providing further evidence of the existence and circulation of reassortant strains on the subcontinent.

Bluetongue virus genetic and phenotypic diversity: towards identifying the molecular determinants that influence virulence and transmission potential

Bluetongue virus (BTV) is the prototype member of the Orbivirus genus in the family Reoviridae and is the aetiological agent of the arthropod transmitted disease bluetongue (BT) that affects both ruminant and camelid species. The disease is of significant global importance due to its economic impact and effect on animal welfare. Bluetongue virus, a dsRNA virus, evolves through a process of quasispecies evolution that is driven by genetic drift and shift as well as intragenic recombination. Quasispecies evolution coupled with founder effect and evolutionary selective pressures has over time led to the establishment of genetically distinct strains of the virus in different epidemiological systems throughout the world. Bluetongue virus field strains may differ substantially from each other with regards to their phenotypic properties (i.e. virulence and/or transmission potential). The intrinsic molecular determinants that influence the phenotype of BTV have not clearly been characterized. It is currently unclear what contribution each of the viral genome segments have in determining the phenotypic properties of the virus and it is also unknown how genetic variability in the individual viral genes and their functional domains relate to differences in phenotype. In order to understand how genetic variation in particular viral genes could potentially influence the phenotypic properties of the virus; a closer understanding of the BTV virion, its encoded proteins and the evolutionary mechanisms that shape the diversity of the virus is required. This review provides a synopsis of these issues and highlights some of the studies that have been conducted on BTV and the closely related African horse sickness virus (AHSV) that have contributed to ongoing attempts to identify the molecular determinants that influence the virus' phenotype. Different strategies that can be used to generate BTV mutants in vitro and methods through which the causality between particular genetic modifications and changes in phenotype may be determined are also described. Finally examples are highlighted where a clear understanding of the molecular determinants that influence the phenotype of the virus may have contributed to risk assessment and mitigation strategies during recent outbreaks of BT in Europe.