The Timing and Magnitude of the Type I Interferon Response Are Correlated with Disease Tolerance in Arbovirus Infection.

Infected hosts possess two alternative strategies to protect themselves against the negative impact of virus infections: resistance, used to abrogate virus replication, and disease tolerance, used to avoid tissue damage without controlling viral burden. The principles governing pathogen resistance are well understood, while less is known about those involved in disease tolerance. Here, we studied bluetongue virus (BTV), the cause of bluetongue disease of ruminants, as a model system to investigate the mechanisms of virus-host interactions correlating with disease tolerance. BTV induces clinical disease mainly in sheep, while cattle are considered reservoirs of infection, rarely exhibiting clinical symptoms despite sustained viremia. Using primary cells from multiple donors, we show that BTV consistently reaches higher titers in ovine cells than cells from cattle. The variable replication kinetics of BTV in sheep and cow cells were mostly abolished by abrogating the cell type I interferon (IFN) response. We identified restriction factors blocking BTV replication, but both the sheep and cow orthologues of these antiviral genes possess anti-BTV properties. Importantly, we demonstrate that BTV induces a faster host cell protein synthesis shutoff in primary sheep cells than cow cells, which results in an earlier downregulation of antiviral proteins. Moreover, by using RNA sequencing (RNA-seq), we also show a more pronounced expression of interferon-stimulated genes (ISGs) in BTV-infected cow cells than sheep cells. Our data provide a new perspective on how the type I IFN response in reservoir species can have overall positive effects on both virus and host evolution. IMPORTANCE The host immune response usually aims to inhibit virus replication in order to avoid cell damage and disease. In some cases, however, the infected host avoids the deleterious effects of infection despite high levels of viral replication. This strategy is known as disease tolerance, and it is used by animal reservoirs of some zoonotic viruses. Here, using a virus of ruminants (bluetongue virus [BTV]) as an experimental system, we dissected virus-host interactions in cells collected from species that are susceptible (sheep) or tolerant (cow) to disease. We show that (i) virus modulation of the host antiviral type I interferon (IFN) responses, (ii) viral replication kinetics, and (iii) virus-induced cell damage differ in tolerant and susceptible BTV-infected cells. Understanding the complex virus-host interactions in disease tolerance can allow us to disentangle the critical balance between protective and damaging host immune responses.

Innate sensing of picornavirus infection involves cGAS-STING-mediated antiviral responses triggered by mitochondrial DNA release.

Cyclic GMP-AMP synthase (cGAS) plays a key role in the innate immune responses to both DNA and RNA virus infection. Here, we found that enterovirus 71 (EV-A71), Seneca Valley virus (SVV), and foot-and-mouth disease virus (FMDV) infection triggered mitochondria damage and mitochondrial DNA (mtDNA) release in vitro and vivo. These responses were mediated by picornavirus 2B proteins which induced mtDNA release during viral replication. SVV infection caused the opening of mitochondrial permeability transition pore (mPTP) and led to voltage-dependent anion channel 1 (VDAC1)- and BCL2 antagonist/killer 1 (Bak) and Bak/BCL2-associated X (Bax)-dependent mtDNA leakage into the cytoplasm, while EV-A71 and FMDV infection induced mPTP opening and resulted in VDAC1-dependent mtDNA release. The released mtDNA bound to cGAS and activated cGAS-mediated antiviral immune response. cGAS was essential for inhibiting EV-A71, SVV, and FMDV replication by regulation of IFN-ß production. cGAS deficiency contributed to higher mortality of EV-A71- or FMDV-infected mice. In addition, we found that SVV 2C protein was responsible for decreasing cGAS expression through the autophagy pathway. The 9th and 153rd amino acid sites in 2C were critical for induction of cGAS degradation. Furthermore, we also show that EV-A71, CA16, and EMCV 2C antagonize the cGAS-stimulator of interferon genes (STING) pathway through interaction with STING, and highly conserved amino acids Y155 and S156 were critical for this inhibitory effect. In conclusion, these data reveal novel mechanisms of picornaviruses to block the antiviral effect mediated by the cGAS-STING signaling pathway, which will provide insights for developing antiviral strategies against picornaviruses.

Identification of diffusion routes of O/EA-3 topotype of foot-and-mouth disease virus in Africa and Western Asia between 1974 and 2019 - a phylogeographic analysis.

Foot-and-mouth disease (FMD) affects the livestock industry and socioeconomic sustainability of many African countries. The success of FMD control programs in Africa depends largely on understanding the dynamics of FMD virus (FMDV) spread. In light of the recent outbreaks of FMD that affected the North-Western African countries in 2018 and 2019, we investigated the evolutionary phylodynamics of the causative serotype O viral strains all belonging to the East-Africa 3 topotype (O/EA-3). We analyzed a total of 489 sequences encoding the FMDV VP1 genome region generated from samples collected from 25 African and Western Asian countries between 1974 and 2019. Using Bayesian evolutionary models on genomic and epidemiological data, we inferred the routes of introduction and migration of the FMDV O/EA-3 topotype at the inter-regional scale. We inferred a mean substitution rate of 6.64 × 10-3  nt/site/year and we predicted that the most recent common ancestor for our panel of samples circulated between February 1967 and November 1973 in Yemen, likely reflecting the epidemiological situation in under sampled cattle-exporting East African countries. Our study also reinforces the role previously described of Sudan and South Sudan as a frequent source of FMDVs spread. In particular, we identified two transboundary routes of O/EA-3 diffusion: the first from Sudan to North-East Africa, and from the latter into Israel and Palestine AT; a second from Sudan to Nigeria, Cameroon, and from there to further into West and North-West Africa. This study highlights the necessity to reinforce surveillance at an inter-regional scale in Africa and Western Asia, in particular along the identified migration routes for the implementation of efficient control measures in the fight against FMD.

Avidity of Polyclonal Antibodies to Foot-and-Mouth Disease Virus in Bovine Serum Measured Using Bio-Layer Interferometry.

Foot-and-mouth disease (FMD) is a disease of cloven-hoofed livestock caused by FMD virus (FMDV). FMD can be controlled through the use of inactivated vaccines, and it is well established that the protection afforded by FMD vaccines correlates strongly with neutralising antibody titres. However, the overall strength of binding, referred to as avidity, is also an important parameter with respect to the ability of antibodies to neutralise virus infection, and there is evidence that avidity can affect the level of protection afforded by FMDV vaccines. Here, as an alternative to modified enzyme-linked immunosorbent assays (avidity ELISAs) incorporating a chaotropic wash step, we used bio-layer interferometry (BLI) to measure the avidity of bovine polyclonal antibodies against FMDV capsids. We conducted preliminary experiments using recombinant FMDV capsids, as well as peptides representing antigenic loops, to demonstrate that the binding of monoclonal antibodies targeting specific antigenic sites could be detected using BLI. Subsequent experiments using polyclonal sera derived from FMD vaccinated cattle provided evidence of a positive correlation between the neutralising titre of the serum and the avidity as measured by BLI. Furthermore, we observed an increase in BLI avidity, as well as in the titre, in vaccinated animals upon challenge with the live virus.

The antiviral state has shaped the CpG composition of the vertebrate interferome to avoid self-targeting.

Antiviral defenses can sense viral RNAs and mediate their destruction. This presents a challenge for host cells since they must destroy viral RNAs while sparing the host mRNAs that encode antiviral effectors. Here, we show that highly upregulated interferon-stimulated genes (ISGs), which encode antiviral proteins, have distinctive nucleotide compositions. We propose that self-targeting by antiviral effectors has selected for ISG transcripts that occupy a less self-targeted sequence space. Following interferon (IFN) stimulation, the CpG-targeting antiviral effector zinc-finger antiviral protein (ZAP) reduces the mRNA abundance of multiple host transcripts, providing a mechanistic explanation for the repression of many (but not all) interferon-repressed genes (IRGs). Notably, IRGs tend to be relatively CpG rich. In contrast, highly upregulated ISGs tend to be strongly CpG suppressed. Thus, ZAP is an example of an effector that has not only selected compositional biases in viral genomes but also appears to have notably shaped the composition of host transcripts in the vertebrate interferome.

Characterising Foot-and-Mouth Disease Virus in Clinical Samples Using Nanopore Sequencing.

The sequencing of viral genomes provides important data for the prevention and control of foot-and-mouth disease (FMD) outbreaks. Sequence data can be used for strain identification, outbreak tracing, and aiding the selection of the most appropriate vaccine for the circulating strains. At present, sequencing of FMD virus (FMDV) relies upon the time-consuming transport of samples to well-resourced laboratories. The Oxford Nanopore Technologies' MinION portable sequencer has the potential to allow sequencing in remote, decentralised laboratories closer to the outbreak location. In this study, we investigated the utility of the MinION to generate sequence data of sufficient quantity and quality for the characterisation of FMDV serotypes O, A, Asia 1. Prior to sequencing, a universal two-step RT-PCR was used to amplify parts of the 5'UTR, as well as the leader, capsid and parts of the 2A encoding regions of FMDV RNA extracted from three sample matrices: cell culture supernatant, tongue epithelial suspension and oral swabs. The resulting consensus sequences were compared with reference sequences generated on the Illumina MiSeq platform. Consensus sequences with an accuracy of 100% were achieved within 10 and 30 min from the start of the sequencing run when using RNA extracted from cell culture supernatants and tongue epithelial suspensions, respectively. In contrast, sequencing from swabs required up to 2.5 h. Together these results demonstrated that the MinION sequencer can be used to accurately and rapidly characterise serotypes A, O, and Asia 1 of FMDV using amplicons amplified from a variety of different sample matrices.

Foot-and-mouth disease virus infection in the domestic dog (Canis lupus familiaris), Iran.

BACKGROUND: Foot-and-mouth disease (FMD) is a highly infectious viral disease, recognised to affect animals in the order Artiodactyla. The disease is rarely fatal in adult animals, however high mortality is associated with neonatal and juvenile infection. CASE PRESENTATION: Five puppies died after being fed lamb carcases, the lambs having died during an outbreak of FMD in Iran. Following a post-mortem examination, cardiac tissue from one of the dead puppies was subjected to virus isolation, antigen ELISA, real-time RT-PCR, sequencing and confocal microscopy to assess the presence and characteristics of any FMD virus. The virological and microscopic examination of the cardiac tissue provided evidence of FMD virus replication in the canine heart. CONCLUSIONS: The data generated in this study demonstrate for the first time that FMD virus can internalise and replicate in dogs and may represent an epidemiologically significant event in FMD transmission, highlighting the dangers of feeding diseased animal carcases to other species. The reporting of this finding may also focus attention on similar disease presentations in dogs in FMD endemic countries allowing a better understanding of the prevalence of such events.

Using noninvasive metagenomics to characterize viral communities from wildlife.

Microbial communities play an important role in organismal and ecosystem health. While high-throughput metabarcoding has revolutionized the study of bacterial communities, generating comparable viral communities has proven elusive, particularly in wildlife samples where the diversity of viruses and limited quantities of viral nucleic acid present distinctive challenges. Metagenomic sequencing is a promising solution for studying viral communities, but the lack of standardized methods currently precludes comparisons across host taxa or localities. Here, we developed an untargeted shotgun metagenomic sequencing protocol to generate comparable viral communities from noninvasively collected faecal and oropharyngeal swabs. Using samples from common vampire bats (Desmodus rotundus), a key species for virus transmission to humans and domestic animals, we tested how different storage media, nucleic acid extraction procedures and enrichment steps affect viral community detection. Based on finding viral contamination in foetal bovine serum, we recommend storing swabs in RNAlater or another nonbiological medium. We recommend extracting nucleic acid directly from swabs rather than from supernatant or pelleted material, which had undetectable levels of viral RNA. Results from a low-input RNA library preparation protocol suggest that ribosomal RNA depletion and light DNase treatment reduce host and bacterial nucleic acid, and improve virus detection. Finally, applying our approach to twelve pooled samples from seven localities in Peru, we showed that detected viral communities saturated at the attained sequencing depth, allowing unbiased comparisons of viral community composition. Future studies using the methods outlined here will elucidate the determinants of viral communities across host species, environments and time.

Interferon-Stimulated Gene (ISG)-Expression Screening Reveals the Specific Antibunyaviral Activity of ISG20.

Bunyaviruses pose a significant threat to human health, prosperity, and food security. In response to viral infections, interferons (IFNs) upregulate the expression of hundreds of interferon-stimulated genes (ISGs), whose cumulative action can potently inhibit the replication of bunyaviruses. We used a flow cytometry-based method to screen the ability of ∼500 unique ISGs from humans and rhesus macaques to inhibit the replication of Bunyamwera orthobunyavirus (BUNV), the prototype of both the Peribunyaviridae family and the Bunyavirales order. Candidates possessing antibunyaviral activity were further examined using a panel of divergent bunyaviruses. Interestingly, one candidate, ISG20, exhibited potent antibunyaviral activity against most viruses examined from the Peribunyaviridae, Hantaviridae, and Nairoviridae families, whereas phleboviruses (Phenuiviridae) largely escaped inhibition. Similar to the case against other viruses known to be targeted by ISG20, the antibunyaviral activity of ISG20 is dependent upon its functional RNase activity. Through use of an infectious virus-like particle (VLP) assay (based on the BUNV minigenome system), we confirmed that gene expression from all 3 viral segments is strongly inhibited by ISG20. Using in vitro evolution, we generated a substantially ISG20-resistant BUNV and mapped the determinants of ISG20 sensitivity/resistance. Taking all the data together, we report that ISG20 is a broad and potent antibunyaviral factor but that some bunyaviruses are remarkably ISG20 resistant. Thus, ISG20 sensitivity/resistance may influence the pathogenesis of bunyaviruses, many of which are emerging viruses of clinical or veterinary significance.IMPORTANCE There are hundreds of bunyaviruses, many of which cause life-threatening acute diseases in humans and livestock. The interferon (IFN) system is a key component of innate immunity, and type I IFNs limit bunyaviral propagation both in vitro and in vivo Type I IFN signaling results in the upregulation of hundreds of IFN-stimulated genes (ISGs), whose concerted action generates an "antiviral state." Although IFNs are critical in limiting bunyaviral replication and pathogenesis, much is still unknown about which ISGs inhibit bunyaviruses. Using ISG-expression screening, we examined the ability of ∼500 unique ISGs to inhibit Bunyamwera orthobunyavirus (BUNV), the prototypical bunyavirus. Using this approach, we identified ISG20, an interferon-stimulated exonuclease, as a potent inhibitor of BUNV. Interestingly, ISG20 possesses highly selective antibunyaviral activity, with multiple bunyaviruses being potently inhibited while some largely escape inhibition. We speculate that the ability of some bunyaviruses to escape ISG20 may influence their pathogenesis.

Fundamental properties of the mammalian innate immune system revealed by multispecies comparison of type I interferon responses.

The host innate immune response mediated by type I interferon (IFN) and the resulting up-regulation of hundreds of interferon-stimulated genes (ISGs) provide an immediate barrier to virus infection. Studies of the type I 'interferome' have mainly been carried out at a single species level, often lacking the power necessary to understand key evolutionary features of this pathway. Here, using a single experimental platform, we determined the properties of the interferomes of multiple vertebrate species and developed a webserver to mine the dataset. This approach revealed a conserved 'core' of 62 ISGs, including genes not previously associated with IFN, underscoring the ancestral functions associated with this antiviral host response. We show that gene expansion contributes to the evolution of the IFN system and that interferomes are shaped by lineage-specific pressures. Consequently, each mammal possesses a unique repertoire of ISGs, including genes common to all mammals and others unique to their specific species or phylogenetic lineages. An analysis of genes commonly down-regulated by IFN suggests that epigenetic regulation of transcription is a fundamental aspect of the IFN response. Our study provides a resource for the scientific community highlighting key paradigms of the type I IFN response.

Bluetongue Virus NS4 Protein Is an Interferon Antagonist and a Determinant of Virus Virulence.

UNLABELLED: Bluetongue virus (BTV) is the causative agent of bluetongue, a major infectious disease of ruminants with serious consequences to both animal health and the economy. The clinical outcome of BTV infection is highly variable and dependent on a variety of factors related to both the virus and the host. In this study, we show that the BTV nonstructural protein NS4 favors viral replication in sheep, the animal species most affected by bluetongue. In addition, NS4 confers a replication advantage on the virus in interferon (IFN)-competent primary sheep endothelial cells and immortalized cell lines. We determined that in cells infected with an NS4 deletion mutant (BTV8ΔNS4), there is increased synthesis of type I IFN compared to cells infected with wild-type BTV-8. In addition, using RNA sequencing (RNA-seq), we show that NS4 modulates the host IFN response and downregulates mRNA levels of type I IFN and interferon-stimulated genes. Moreover, using reporter assays and protein synthesis assays, we show that NS4 downregulates the activities of a variety of promoters, such as the cytomegalovirus immediate-early promoter, the IFN-ß promoter, and a promoter containing interferon-stimulated response elements (ISRE). We also show that the NS4 inhibitory activity on gene expression is related to its nucleolar localization. Furthermore, NS4 does not affect mRNA splicing or cellular translation. The data obtained in this study strongly suggest that BTV NS4 is an IFN antagonist and a key determinant of viral virulence. IMPORTANCE: Bluetongue is one of the main infectious diseases of ruminants and is caused by bluetongue virus (BTV), an arthropod-borne virus transmitted from infected to susceptible animals by Culicoides biting midges. Bluetongue has a variable clinical outcome that can be related to both virus and host factors. It is therefore critical to understand the interplay between BTV and the host immune responses. In this study, we show that a nonstructural protein of BTV (NS4) is critical to counteract the innate immune response of the host. Infection of cells with a BTV mutant lacking NS4 results in increased synthesis of IFN-ß and upregulation of interferon-stimulated genes. In addition, we show that NS4 is a virulence factor for BTV by favoring viral replication in sheep, the animal species most susceptible to bluetongue.

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.

RNA interference targets arbovirus replication in Culicoides cells.

Arboviruses are transmitted to vertebrate hosts by biting arthropod vectors such as mosquitoes, ticks, and midges. These viruses replicate in both arthropods and vertebrates and are thus exposed to different antiviral responses in these organisms. RNA interference (RNAi) is a sequence-specific RNA degradation mechanism that has been shown to play a major role in the antiviral response against arboviruses in mosquitoes. Culicoides midges are important vectors of arboviruses, known to transmit pathogens of humans and livestock such as bluetongue virus (BTV) (Reoviridae), Oropouche virus (Bunyaviridae), and likely the recently discovered Schmallenberg virus (Bunyaviridae). In this study, we investigated whether Culicoides cells possess an antiviral RNAi response and whether this is effective against arboviruses, including those with double-stranded RNA (dsRNA) genomes, such as BTV. Using reporter gene-based assays, we established the presence of a functional RNAi response in Culicoides sonorensis-derived KC cells which is effective in inhibiting BTV infection. Sequencing of small RNAs from KC and Aedes aegypti-derived Aag2 cells infected with BTV or the unrelated Schmallenberg virus resulted in the production of virus-derived small interfering RNAs (viRNAs) of 21 nucleotides, similar to the viRNAs produced during arbovirus infections of mosquitoes. In addition, viRNA profiles strongly suggest that the BTV dsRNA genome is accessible to a Dicer-type nuclease. Thus, we show for the first time that midge cells target arbovirus replication by mounting an antiviral RNAi response mainly resembling that of other insect vectors of arboviruses.

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.

Drosophila melanogaster as a model organism for bluetongue virus replication and tropism.

Bluetongue virus (BTV) is the etiological agent of bluetongue (BT), a hemorrhagic disease of ruminants that can cause high levels of morbidity and mortality. BTV is an arbovirus transmitted between its ruminant hosts by Culicoides biting midges (Diptera: Ceratopogonidae). Recently, Europe has experienced some of the largest BT outbreaks ever recorded, including areas with no known history of the disease, leading to unprecedented economic and animal welfare issues. The current lack of genomic resources and genetic tools for Culicoides restricts any detailed study of the mechanisms involved in the virus-insect interactions. In contrast, the genome of the fruit fly (Drosophila melanogaster) has been successfully sequenced, and it is used extensively as a model of molecular pathways due to the existence of powerful genetic technology. In this study, D. melanogaster is investigated as a model for the replication and tropism of BTV. Using reverse genetics, a modified BTV-1 that expresses the fluorescent mCherry protein fused to the viral nonstructural protein NS3 (BTV-1/NS3mCherry) was generated. We demonstrate that BTV-1/NS3mCherry is not only replication competent as it retains many characteristics of the wild-type virus but also replicates efficiently in D. melanogaster after removal of the bacterial endosymbiont Wolbachia pipientis by antibiotic treatment. Furthermore, confocal microscopy shows that the tissue tropism of BTV-1/NS3mCherry in D. melanogaster resembles that described previously for BTV in Culicoides. Overall, the data presented in this study demonstrate the feasibility of using D. melanogaster as a genetic model to investigate BTV-insect interactions that cannot be otherwise addressed in vector species.

Integrin sub-unit expression in cell cultures used for the diagnosis of foot-and-mouth disease.

The ability to propagate foot-and-mouth disease virus (FMDV) plays an important role in laboratory diagnosis and the production of vaccines to control the spread of the disease. Many established cell lines suffer from poor sensitivity for isolating virus from field samples. One possible factor that limits sensitivity to FMDV is the lack of expression of surface integrins, the primary class of cell receptor used by FMDV to initiate infection. In this study we have sequenced cDNAs encoding these molecules for pigs and subsequently developed quantitative real-time reverse transcription (RT)-PCR assays to quantify underlying mRNA transcription of integrin molecules. These novel assays were used together with flow-cytometry to determine cell surface expression and of 4 different cell culture systems. These studies have identified a clear correlation of sensitivity to FMDV with expression of integrins αVß6 and αVß8. In contrast, cell surface expression of αVß3 or mRNA for the ß1, ß3 or ß5 subunits did not appear to contribute to sensitivity of cells to FMDV. These findings confirm the requirement for αV6 and αVß8 as receptors for isolating FMDV from clinical samples and provide important tools and information for the rational design of recombinant cell lines containing these ligands for improved FMDV diagnosis and vaccine production.

Performance of real-time reverse transcription polymerase chain reaction for the detection of foot-and-mouth disease virus during field outbreaks in the United Kingdom in 2007.

Rapid and accurate diagnosis is essential for effective control of foot-and-mouth disease (FMD). The present report describes the practical steps undertaken to deploy a real-time reverse transcription polymerase chain reaction (real-time RT-PCR) to process the samples received during the outbreaks of FMD in the United Kingdom in 2007. Two independent real-time RT-PCR assays targeting different regions (5'UTR and 3D) of the FMD virus (FMDV) genome were used to confirm the presence of FMDV in clinical samples collected from the first infected premises. Once the FMDV strain responsible had been sequenced, a single real-time RT-PCR assay (3D) was selected to test a total of 3,216 samples, including material from all 8 infected premises. Using a 96-well automated system to prepare nucleic acid template, up to 84 samples could be processed within 5 hr of submission, and up to 269 samples were tested per working day. A conservative cut-off was used to designate positive samples, giving rise to an assay specificity of 99.9% or 100% for negative control material or samples collected from negative premises, respectively. For the first time, real-time RT-PCR results were used to recognize preclinical FMD in a cattle herd. Furthermore, during the later stages of the outbreaks, the real-time RT-PCR assay supported an active surveillance program within high-risk cattle herds. To the authors' knowledge, this is the first documented use of real-time RT-PCR as a principal laboratory diagnostic tool following introduction of FMD into a country that was FMD-free (without vaccination) and highlights the advantages of this assay to support control decisions during disease outbreaks.

A European field strain of bluetongue virus derived from two parental vaccine strains by genome segment reassortment.

Since 1998, nine bluetongue virus (BTV) strains from serotypes 1, 2, 4, 8, 9 and 16 have invaded Europe, killing >2 million animals (mainly sheep). Live vaccine strains of BTV-2, 4, 9 and 16 have also been used in the region. The BTV genome is composed of ten linear-segments of dsRNA, and events in Europe have provided opportunities for different strains to exchange/reassort genome segments, generating novel progeny-viruses. Genome segment 2 (Seg-2) encodes outer capsid protein VP2, the primary determinant of virus serotype, while Seg-5 encodes NS1, which forms 'tubules' within the cell-cytoplasm. Seg-2 and Seg-5 from 15 European isolates, and vaccine/reference strains, of BTV-2 and BTV-16, were sequenced. Isolates from the same serotype showed >92% nt identity in Seg-5, but <84% identity between types. However, published data for Seg-5 of BTV-16 from Italy 2002 showed <83% nt identity with other BTV-16 strains, but was identical to the BTV-2 vaccine strain (used in Italy during 2002, and annually in a multivalent vaccine in Israel since 1995) indicating that ITL2002 is a reassortant between the BTV-2 and BTV-16 vaccine strains. This represents the first detection of a reassortant BTV strain within Europe, highlighting concerns about the use of live BTV vaccines in the region.

Sequence analysis of bluetongue virus serotype 8 from the Netherlands 2006 and comparison to other European strains.

During 2006 the first outbreak of bluetongue ever recorded in northern Europe started in Belgium and the Netherlands, spreading to Luxemburg, Germany and north-east France. The virus overwintered (2006-2007) reappearing during May-June 2007 with greatly increased severity in affected areas, spreading further into Germany and France, reaching Denmark, Switzerland, the Czech Republic and the UK. Infected animals were also imported into Poland, Italy, Spain and the UK. An initial isolate from the Netherlands (NET2006/04) was identified as BTV-8 by RT-PCR assays targeting genome segment 2. The full genome of NET2006/04 was sequenced and compared to selected European isolates, South African vaccine strains and other BTV-8 strains, indicating that it originated in sub-Saharan Africa. Although NET2006/04 showed high levels of nucleotide identity with other 'western' BTV strains, it represents a new introduction and was not derived from the BTV-8 vaccine, although its route of entry into Europe has not been established.

Transmission pathways of foot-and-mouth disease virus in the United Kingdom in 2007.

Foot-and-mouth disease (FMD) virus causes an acute vesicular disease of domesticated and wild ruminants and pigs. Identifying sources of FMD outbreaks is often confounded by incomplete epidemiological evidence and the numerous routes by which virus can spread (movements of infected animals or their products, contaminated persons, objects, and aerosols). Here, we show that the outbreaks of FMD in the United Kingdom in August 2007 were caused by a derivative of FMDV O(1) BFS 1860, a virus strain handled at two FMD laboratories located on a single site at Pirbright in Surrey. Genetic analysis of complete viral genomes generated in real-time reveals a probable chain of transmission events, predicting undisclosed infected premises, and connecting the second cluster of outbreaks in September to those in August. Complete genome sequence analysis of FMD viruses conducted in real-time have identified the initial and intermediate sources of these outbreaks and demonstrate the value of such techniques in providing information useful to contemporary disease control programmes.