Establishment of a bluetongue virus infection model in mice that are deficient in the alpha/beta interferon receptor

Increased Virulence of Culicoides Midge Cell-Derived Bluetongue Virus in IFNAR Mice

Bluetongue (BT) is a Culicoides midge-borne hemorrhagic disease affecting cervids and ruminant livestock species, resulting in significant economic losses from animal production and trade restrictions. Experimental animal infections using the α/β interferon receptor knockout IFNAR mouse model and susceptible target species are critical for understanding viral pathogenesis, virulence, and evaluating vaccines. However, conducting experimental vector-borne transmission studies with the vector itself are logistically difficult and experimentally problematic. Therefore, experimental infections are induced by hypodermic injection with virus typically derived from baby hamster kidney (BHK) cells. Unfortunately, for many U.S. BTV serotypes, it is difficult to replicate the severity of the disease seen in natural, midge-transmitted infections by injecting BHK-derived virus into target host animals. Using the IFNAR BTV murine model, we compared the virulence of traditional BHK cell-derived BTV-17 with C. sonorensis midge (W8) cell-derived BTV-17 to determine whether using cells of the transmission vector would provide an in vitro virulence aspect of vector-transmitted virus. At both low and high doses, mice inoculated with W8-BTV-17 had an earlier onset of viremia, earlier onset and peak of clinical signs, and significantly higher mortality compared to mice inoculated with BHK-BTV-17. Our results suggest using a Culicoides W8 cell-derived inoculum may provide an in vitro vector-enhanced infection to more closely represent disease levels seen in natural midge-transmitted infections while avoiding the logistical and experimental complexity of working with live midges.

Immuno-informatics study identifies conserved T cell epitopes in non-structural proteins of Bluetongue virus serotypes: formulation of a computationally optimized next-generation broad-spectrum multi-epitope vaccine

Introduction

Bluetongue (BT) poses a significant threat to the livestock industry, affecting various animal species and resulting in substantial economic losses. The existence of numerous BT virus (BTV) serotypes has hindered control efforts, highlighting the need for broad-spectrum vaccines.

Methodology

In this study, we evaluated the conserved amino acid sequences within key non-structural (NS) proteins of BTV and identified numerous highly conserved murine- and bovine-specific MHC class I-restricted (MHC-I) CD8+ and MHC-II-restricted CD4+ epitopes. We then screened these conserved epitopes for antigenicity, allergenicity, toxicity, and solubility. Using these epitopes, we developed in silico-based broad-spectrum multiepitope vaccines with Toll-like receptor (TLR-4) agonists. The predicted proinflammatory cytokine response was assessed in silico using the C-IMMSIM server. Structural modeling and refinement were achieved using Robetta and GalaxyWEB servers. Finally, we assessed the stability of the docking complexes through extensive 100-nanosecond molecular dynamics simulations before considering the vaccines for codon optimization and in silico cloning.

Results

We found many epitopes that meet these criteria within NS1 and NS2 proteins and developed in silico broad-spectrum vaccines. The immune simulation studies revealed that these vaccines induce high levels of IFN-γ and IL-2 in the vaccinated groups. Protein-protein docking analysis demonstrated promising epitopes with strong binding affinities to TLR-4. The docked complexes were stable, with minimal Root Mean Square Deviation and Root Mean Square Fluctuation values. Finally, the in silico-cloned plasmids have high % of GC content with > 0.8 codon adaptation index, suggesting they are suitable for expressing the protein vaccines in prokaryotic system.

Discussion

These next-generation vaccine designs are promising and warrant further investigation in wet lab experiments to assess their immunogenicity, safety, and efficacy for practical application in livestock. Our findings offer a robust framework for developing a comprehensive, broad-spectrum vaccine, potentially revolutionizing BT control and prevention strategies in the livestock industry.

IFNAR(-/-) Mice Constitute a Suitable Animal Model for Epizootic Hemorrhagic Disease Virus Study and Vaccine Evaluation

Epizootic hemorrhagic disease (EHD), caused by Epizootic hemorrhagic disease virus (EHDV), is an emerging and severe livestock disease. Recent incursion and distribution of EHDV in Europe have outlined the emerging character of EHD. Despite its worldwide impact, numerous knowledge gaps exist. A range of inconveniences restricts utilization of natural hosts of EHDV. Here, we show that adult mice deficient in type I IFN receptor (IFNAR(-/-)) are highly susceptible to EHDV-6 and EHDV-8 infection when the virus is administered subcutaneously. Disease was characterized by ruffled hair, reluctance to move, dehydration and conjunctivitis, with viraemia detected from day 5 post-infection. A deeper characterization of EHDV-8 infection showed viral replication in the lung, liver, spleen, kidney, testis and ovaries. Importantly, increased expression levels of pro-inflammatory cytokines IL-1β, IL-6 and CXCL2 were observed in spleen after EHDV-8 infection. Furthermore, IFNAR(-/-) adult mice immunized with a EHDV-8 inactivated vaccine elicited neutralizing antibodies specific of EHDV-8 and full protection against challenge with a lethal dose of this virus. This study also explores the possibilities of this animal model for study of BTV and EHDV coinfection. In summary, the IFNAR(-/-) mouse model faithfully recapitulates EHD and can be applied for vaccine testing, which can facilitate progress in addressing the animal health challenge posed by this virus.

Age- and Sex-Associated Pathogenesis of Cell Culture-Passaged Kemerovo Virus in IFNAR(-/-) Mice

Kemerovo virus (KEMV) is a tick-borne orbivirus transmitted by ticks of the genus Ixodes. Previous animal experimentation studies with orbiviruses, in particular the interferon receptor double knock-out (IFNAR(-/-)) mouse model, did not indicate bias that is related to age or sex. We endeavoured to assess the effect of serial and alternated passages of KEMV in mammalian or Ixodes cells on virus replication and potential virulence in male or female IFNAR(-/-) mice, with important age differences: younger males (4-5 months old), older males (14-15 months old), and old females (14-15 months old). After 30 serial passages in mammalian or tick cells, or alternated passages in the two cell types, older female mice which were inoculated with the resulting virus strains were the first to show clinical signs and die. Younger males behaved differently from older males whether they were inoculated with the parental strain of KEMV or with any of the cell culture-passaged strains. The groups of male and female mice inoculated with the mammalian cell culture-adapted KEMV showed the lowest viraemia. While older female and younger male mice died by day 6 post-inoculation, surprisingly, the older males survived until the end of the experiment, which lasted 10 days. RNA extracted from blood and organs of the various mice was tested by probe-based KEMV real-time RT-PCR. Ct values of the RNA extracts were comparable between older females and younger males, while the values for older males were >5 Ct units higher for the various organs, indicating lower levels of replication. It is noteworthy that the hearts of the old males were the only organs that were negative for KEMV RNA. These results suggest, for the first time, an intriguing age- and sex-related bias for an orbivirus in this animal model. Changes in the amino acid sequence of the RNA-dependent RNA polymerase of Kemerovo virus, derived from the first serial passage in Ixodes cells (KEMV Ps.IRE1), were identified in the vicinity of the active polymerase site. This finding suggests that selection of a subpopulation of KEMV with better replication fitness in tick cells occurred.

Engineering recombinant replication-competent bluetongue viruses expressing reporter genes for in vitro and non-invasive in vivo studies

Bluetongue virus (BTV) is the causative agent of the important livestock disease bluetongue (BT), which is transmitted via Culicoides bites. BT causes severe economic losses associated with its considerable impact on health and trade of animals. By reverse genetics, we have designed and rescued reporter-expressing recombinant (r)BTV expressing NanoLuc luciferase (NLuc) or Venus fluorescent protein. To generate these viruses, we custom synthesized a modified viral segment 5 encoding NS1 protein with the reporter genes located downstream and linked by the Porcine teschovirus-1 (PTV-1) 2A autoproteolytic cleavage site. Therefore, fluorescent signal or luciferase activity is only detected after virus replication and expression of non-structural proteins. Fluorescence or luminescence signals were detected in cells infected with rBTV/Venus or rBTV/NLuc, respectively. Moreover, the marking of NS2 protein confirmed that reporter genes were only expressed in BTV-infected cells. Growth kinetics of rBTV/NLuc and rBTV/Venus in Vero cells showed replication rates similar to those of wild-type and rBTV. Infectivity studies of these recombinant viruses in IFNAR(-/-) mice showed a higher lethal dose for rBTV/NLuc and rBTV/Venus than for rBTV indicating that viruses expressing the reporter genes are attenuated in vivo. Interestingly, luciferase activity was detected in the plasma of viraemic mice infected with rBTV/NLuc. Furthermore, luciferase activity quantitatively correlated with RNAemia levels of infected mice throughout the infection. In addition, we have investigated the in vivo replication and dissemination of BTV in IFNAR (-/-) mice using BTV/NLuc and non-invasive in vivo imaging systems.IMPORTANCEThe use of replication-competent viruses that encode a traceable fluorescent or luciferase reporter protein has significantly contributed to the in vitro and in vivo study of viral infections and the development of novel therapeutic approaches. In this work, we have generated rBTV that express fluorescent or luminescence proteins to track BTV infection both in vitro and in vivo. Despite the availability of vaccines, BTV and other related orbivirus are still associated with a significant impact on animal health and have important economic consequences worldwide. Our studies may contribute to the advance in orbivirus research and pave the way for the rapid development of new treatments, including vaccines.

Epizootic Hemorrhagic Disease Virus: Current Knowledge and Emerging Perspectives

Epizootic Hemorrhagic Disease (EHD) of ruminants is a viral pathology that has significant welfare, social, and economic implications. The causative agent, epizootic hemorrhagic disease virus (EHDV), belongs to the Orbivirus genus and leads to significant regional disease outbreaks among livestock and wildlife in North America, Asia, Africa, and Oceania, causing significant morbidity and mortality. During the past decade, this viral disease has become a real threat for countries of the Mediterranean basin, with the recent occurrence of several important outbreaks in livestock. Moreover, the European Union registered the first cases of EHDV ever detected within its territory. Competent vectors involved in viral transmission, Culicoides midges, are expanding its distribution, conceivably due to global climate change. Therefore, livestock and wild ruminants around the globe are at risk for this serious disease. This review provides an overview of current knowledge about EHDV, including changes of distribution and virulence, an examination of different animal models of disease, and a discussion about potential treatments to control the disease.

Pathological features of African horse sickness virus infection in IFNAR-/- mice

African Horse Sickness (AHS) is a vector-borne viral disease of equids. The disease can be highly lethal with mortality rates of up to 90% in non-immune equine populations. The clinical presentation in the equine host varies, but the pathogenesis underlying this variation remains incompletely understood. Various small animal models of AHS have been developed over the years to overcome the financial, bio-safety and logistical constraints of studying the pathology of this disease in the target species. One of the most successful small animal models is based on the use of interferon-alpha gene knock-out (IFNAR-/-) mice. In order to increase our understanding of African Horse Sickness virus (AHSV) pathogenesis, we characterised the pathology lesions of AHSV infection in IFNAR-/- mice using a strain of AHSV serotype 4 (AHSV-4). We found AHSV-4 infection was correlated with lesions in various organs; necrosis in the spleen and lymphoid tissues, inflammatory infiltration in the liver and brain, and pneumonia. Significant viral antigen staining was only detected in the spleen and brain, however. Together these results confirm the value of the IFNAR-/- mouse model for the study of the immuno-biology of AHSV infections in this particular in vivo system, and its usefulness for evaluating protective efficacy of candidate vaccines in preclinical studies.

Genetic characteristics and pathogenicity of the first bluetongue virus serotype 20 strain isolated in China

Bluetongue virus (BTV), a member of the genus Orbivirus in the family Reoviridae, is transmitted by biting midges and causes severe disease in domestic and wild ruminants. In the present study, a BTV strain, BTV-20/GX015/China/2013 (GX015), was isolated from sentinel cattle in Guangxi, China. Virus neutralization tests and phylogenetic analyses based on genomic segments 2 (S2) and 6 (S6) indicated that GX015 belongs to BTV serotype 20 (BTV-20) and represents a new topotype within BTV-20 strains, which makes GX015 the first BTV-20 strain isolated in China. Genomic analyses suggested that the 10 genomic segments of GX015 originated from a reassortment event, in which S2 and S6 are derived from exotic BTV-20 strains (South Africa or Australia), whereas the remaining eight genomic segments are apparently of Chinese origin and most likely share the same ancestor with a Taiwanese BTV-12 strain. Importantly, we evaluated the infectivity and pathogenicity of the BTV-20 strain in mice lacking the interferon receptor (IFNAR-/- mice, a good animal model for studying the pathogenesis, virulence and transmission of BTVs) and sheep for the first time, and found that GX015 causes severe disease and death in IFNAR-/- mice and clinical signs and viraemia in the natural host sheep. These results improve our understanding of the genetic characteristics, diversity and pathogenicity of BTVs, which is important for developing diagnostic methods and vaccines for the surveillance and prevention of bluetongue disease.

Nanoparticle- and Microparticle-Based Vaccines against Orbiviruses of Veterinary Importance

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are widespread arboviruses that cause important economic losses in the livestock and equine industries, respectively. In addition to these, another arthropod-transmitted orbivirus known as epizootic hemorrhagic disease virus (EHDV) entails a major threat as there is a conducive landscape that nurtures its emergence in non-endemic countries. To date, only vaccinations with live attenuated or inactivated vaccines permit the control of these three viral diseases, although important drawbacks, e.g., low safety profile and effectiveness, and lack of DIVA (differentiation of infected from vaccinated animals) properties, constrain their usage as prophylactic measures. Moreover, a substantial number of serotypes of BTV, AHSV and EHDV have been described, with poor induction of cross-protective immune responses among serotypes. In the context of next-generation vaccine development, antigen delivery systems based on nano- or microparticles have gathered significant attention during the last few decades. A diversity of technologies, such as virus-like particles or self-assembled protein complexes, have been implemented for vaccine design against these viruses. In this work, we offer a comprehensive review of the nano- and microparticulated vaccine candidates against these three relevant orbiviruses. Additionally, we also review an innovative technology for antigen delivery based on the avian reovirus nonstructural protein muNS and we explore the prospective functionality of the nonstructural protein NS1 nanotubules as a BTV-based delivery platform.

Characterization of a Novel Reassortant Epizootic Hemorrhagic Disease Virus Serotype 6 Strain Isolated from Diseased White-Tailed Deer (Odocoileus virginianus) on a Florida Farm

We report an outbreak of a novel reassortant epizootic hemorrhagic disease virus serotype 6 (EHDV-6) in white-tailed deer (WTD) on a Florida farm in 2019. At necropsy, most animals exhibited hemorrhagic lesions in the lung and heart, and congestion in the lung, liver, and spleen. Histopathology revealed multi-organ hemorrhage and congestion, and renal tubular necrosis. Tissues were screened by RT-qPCR and all animals tested positive for EHDV. Tissues were processed for virus isolation and next-generation sequencing was performed on cDNA libraries generated from the RNA extracts of cultures displaying cytopathic effects. Six isolates yielded nearly identical complete genome sequences of a novel U.S. EHDV-6 strain. Genetic and phylogenetic analyses revealed the novel strain to be most closely related to a reassortant EHDV-6 strain isolated from cattle in Trinidad and both strains received segment 4 from an Australian EHDV-2 strain. The novel U.S. EHDV-6 strain is unique in that it acquired segment 8 from an Australian EHDV-8 strain. An RNAscope® in situ hybridization assay was developed against the novel U.S. EHDV-6 strain and labeling was detected within lesions of the heart, kidney, liver, and lung. These data support the novel U.S. reassortant EHDV-6 strain as the cause of disease in the farmed WTD.

Evaluation of two artificial infection methods of live ticks as tools for studying interactions between tick-borne viruses and their tick vectors

Up to 170 tick-borne viruses (TBVs) have been identified to date. However, there is a paucity of information regarding TBVs and their interaction with respective vectors, limiting the development of new effective and urgently needed control methods. To overcome this gap of knowledge, it is essential to reproduce transmission cycles under controlled laboratory conditions. In this study we assessed an artificial feeding system (AFS) and an immersion technique (IT) to infect Ixodes ricinus ticks with tick-borne encephalitis (TBE) and Kemerovo (KEM) virus, both known to be transmitted predominantly by ixodid ticks. Both methods permitted TBEV acquisition by ticks and we further confirmed virus trans-stadial transmission and onward transmission to a vertebrate host. However, only artificial feeding system allowed to demonstrate both acquisition by ticks and trans-stadial transmission for KEMV. Yet we did not observe transmission of KEMV to mice (IFNAR^-/- or BALB/c). Artificial infection methods of ticks are important tools to study tick-virus interactions. When optimally used under laboratory settings, they provide important insights into tick-borne virus transmission cycles.

Vaccination as a Strategy to Prevent Bluetongue Virus Vertical Transmission

Bluetongue virus (BTV) produces an economically important disease in ruminants of compulsory notification to the OIE. BTV is typically transmitted by the bite of Culicoides spp., however, some BTV strains can be transmitted vertically, and this is associated with fetus malformations and abortions. The viral factors associated with the virus potency to cross the placental barrier are not well defined. The potency of vertical transmission is retained and sometimes even increased in live attenuated BTV vaccine strains. Because BTV possesses a segmented genome, the possibility of reassortment of vaccination strains with wild-type virus could even favor the transmission of this phenotype. In the present review, we will describe the non-vector-based BTV infection routes and discuss the experimental vaccination strategies that offer advantages over this drawback of some live attenuated BTV vaccines.

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

Transboundary Animal Diseases, an Overview of 17 Diseases with Potential for Global Spread and Serious Consequences

Animals provide food and other critical resources to most of the global population. As such, diseases of animals can cause dire consequences, especially disease with high rates of morbidity or mortality. Transboundary animal diseases (TADs) are highly contagious or transmissible, epidemic diseases, with the potential to spread rapidly across the globe and the potential to cause substantial socioeconomic and public health consequences. Transboundary animal diseases can threaten the global food supply, reduce the availability of non-food animal products, or cause the loss of human productivity or life. Further, TADs result in socioeconomic consequences from costs of control or preventative measures, and from trade restrictions. A greater understanding of the transmission, spread, and pathogenesis of these diseases is required. Further work is also needed to improve the efficacy and cost of both diagnostics and vaccines. This review aims to give a broad overview of 17 TADs, providing researchers and veterinarians with a current, succinct resource of salient details regarding these significant diseases. For each disease, we provide a synopsis of the disease and its status, species and geographic areas affected, a summary of in vitro or in vivo research models, and when available, information regarding prevention or treatment.

Inhibition of the IFN Response by Bluetongue Virus: The Story So Far

Bluetongue virus (BTV) is the prototypical orbivirus that belongs to the Reoviridae family. BTV infection produces a disease in ruminants, particularly in sheep, that results in economic losses through reduced productivity. BTV is transmitted by the bite of Culicoides spp. midges and is nowadays distributed globally throughout subtropical and even temperate regions. As most viruses, BTV is susceptible to the IFN response, the first line of defense employed by the immune system to combat viral infections. In turn, BTV has evolved strategies to counter the IFN response and promote its replication. The present review we will revise the works describing how BTV interferes with the IFN response.

Vaccination With Recombinant Adenoviruses Expressing the Bluetongue Virus Subunits VP7 and VP2 Provides Protection Against Heterologous Virus Challenge

Bluetongue virus (BTV) is the causative agent of a disease that affects domestic and wild ruminants and leads to critical economic losses. BTV is an arbovirus from the Reoviridae family that is typically transmitted by the bite of infected Culicoides midges. BTV possesses multiple serotypes (up to 28 have been described), and immunity to one serotype offers little cross-protection to other serotypes. The design of vaccines that provide protection across multiple serotypes is therefore highly desirable to control this disease. We previously reported that a recombinant replication-defective human adenovirus serotype 5 (Ad5) that expresses the VP7 inner core protein of BTV serotype 8 (Ad5VP7-8) induced T-cell responses and provided protection. In the present work, we evaluated as BTV vaccine the combination of Ad5VP7-8 with another recombinant Ad5 that expresses the outer core protein VP2 from BTV-1 (Ad5VP2-1). The combination of Ad5VP2-1 and Ad5VP7-8 protected against homologous BTV challenge (BTV-1 and BTV-8) and partially against heterologous BTV-4 in a murine model. Cross-reactive anti-BTV immunoglobulin G (IgG) were detected in immunized animals, but no significant titers of neutralizing antibodies were elicited. The Ad5VP7-8 immunization induced T-cell responses that recognized all three serotypes tested in this study and primed cytotoxic T lymphocytes specific for VP7. This study further confirms that targeting antigenic determinant shared by several BTV serotypes using cellular immunity could help develop multiserotype BTV vaccines.

Pathological and immunological characterization of bluetongue virus serotype 1 infection in type I interferons blocked immunocompetent adult mice

Introduction

Wild-type adult mice with intact interferon (IFN) system were neither susceptible to bluetongue virus (BTV) infection nor showed signs of morbidity/mortality. Establishment of immunologically competent wild-type adult mouse model with type I IFNs blockade is necessary to assess the pathogenesis, immune responses and testing of BTV vaccines.

Objectives

Present study aimed to establish and characterize BTV serotype 1 infection in immunocompetent adult mice with type I IFNs blockade at the time of infection by studying immune responses and sequential pathology.

Methods

Adult mice were administered with anti-mouse IFN-α/β receptor subunit-1 (IFNAR1) blocking antibody (Clone: MAR1-5A3) 24 h before and after BTV serotype 1 infection, and sacrificed at various time points. Sequential pathology, BTV localization by immunohistochemistry and quantification by qRT-PCR, immune cell kinetics and apoptosis by flow cytometry, and cytokines estimation by c-ELISA and qRT-PCR were studied.

Results

IFNAR blocked-infected mice developed clinical signs and typical lesions of BT; whereas, isotype-infected control mice did not develop any disease. The IFNAR blocked-infected mice showed enlarged, edematous, and congested lymph nodes (LNs) and spleen, and vascular (congestion and hemorrhage) and pneumonic lesions in lungs. Histopathologically, marked lymphoid depletion with “starry-sky pattern” due to lymphocytes apoptosis was noticed in the LNs and spleen. BTV antigen was detected and quantified in lymphoid organs, lungs, and other organs at various time points. Initial leukopenia (increased CD4⁺/CD8⁺ T cells ratio) followed by leukocytosis (decreased CD4⁺/CD8⁺ T cells ratio) and significantly increased biochemical values were noticed in IFNAR blocked-infected mice. Increased apoptotic cells in PBMCs and tissues coincided with viral load and levels of different cytokines in blood, spleen and draining LNs and notably varied between time points in IFNAR blocked-infected mice.

Conclusion

Present study is first to characterize BTV serotype 1 infection in immunocompetent adult mouse with type I IFNs blockade. The findings will be useful for studying pathogenesis and testing the efficacy of BTV vaccines.

Recombinant Rift Valley fever viruses encoding bluetongue virus (BTV) antigens: Immunity and efficacy studies upon a BTV-4 challenge

Background

Many ruminant diseases of viral aetiology can be effectively prevented using appropriate vaccination measures. For diseases such as Rift Valley fever (RVF) the long inter-epizootic periods make routine vaccination programs unfeasible. Coupling RVF prophylaxis with seasonal vaccination programmes by means of multivalent vaccine platforms would help to reduce the risk of new RVF outbreaks.

Methodology/Principal findings

In this work we generated recombinant attenuated Rift Valley fever viruses (RVFVs) encoding in place of the virulence factor NSs either the VP2 capsid protein or a truncated form of the non-structural NS1 protein of bluetongue virus serotype 4 (BTV-4). The recombinant viruses were able to carry and express the heterologous BTV genes upon consecutive passages in cell cultures. In murine models, a single immunization was sufficient to protect mice upon RVFV challenge and to elicit a specific immune response against BTV-4 antigens that was fully protective after a BTV-4 boost. In sheep, a natural host for RVFV and BTV, both vaccines proved immunogenic although conferred only partial protection after a virulent BTV-4 reassortant Morocco strain challenge.

Conclusions/Significance

Though additional optimization will be needed to improve the efficacy data against BTV in sheep, our findings warrant further developments of attenuated RVFV as a dual vaccine platform carrying heterologous immune relevant antigens for ruminant diseases in RVF risk areas.

Live attenuated Rift Valley fever (RVF) vaccines constitute a reliable intervention measure to reduce the burden of the disease in endemic countries. In this work we report the generation of attenuated Rift Valley fever virus (RVFV) that express vaccine antigens of bluetongue virus (BTV) instead of the virulence factor NSs. The recombinant viruses were able to induce protective immune responses against both RVFV and BTV when administered as vaccines in mice and sheep respectively. Though further optimization is needed to enhance the level of protection in sheep upon a single dose, these results demonstrate the potential of attenuated RVFV as a vaccine vector for other ruminant diseases, in this case enabling bluetongue vaccination while immunizing against RVF. Since RVF outbreaks are sporadic events, preventive vaccination is often not perceived as a real need. In such scenario a bivalent vaccine strategy would make RVF vaccination more appealing.

Inhibition of Orbivirus Replication by Aurintricarboxylic Acid

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are vector-borne viruses belonging to the Orbivirus genus, which are transmitted between hosts primarily by biting midges of the genus Culicoides. With recent BTV and AHSV outbreaks causing epidemics and important economy losses, there is a pressing need for efficacious drugs to treat and control the spread of these infections. The polyanionic aromatic compound aurintricarboxylic acid (ATA) has been shown to have a broad-spectrum antiviral activity. Here, we evaluated ATA as a potential antiviral compound against Orbivirus infections in both mammalian and insect cells. Notably, ATA was able to prevent the replication of BTV and AHSV in both cell types in a time- and concentration-dependent manner. In addition, we evaluated the effect of ATA in vivo using a mouse model of infection. ATA did not protect mice against a lethal challenge with BTV or AHSV, most probably due to the in vivo effect of ATA on immune system regulation. Overall, these results demonstrate that ATA has inhibitory activity against Orbivirus replication in vitro, but further in vivo analysis will be required before considering it as a potential therapy for future clinical evaluation.

Recombinant bluetongue virus with hemagglutinin epitopes in VP2 has potential as a labeled vaccine

Bluetongue (BT) is an arbovirus-borne disease of ruminants caused by bluetongue virus (BTV) that has the potential to have a serious economic impact. Currently available commercial vaccines include attenuated vaccines and inactivated vaccines, both of which have achieved great success in the prevention and control of BTV. However, these vaccines cannot distinguish between infected animals and immunized animals. To control outbreaks of BTV, the development of labeled vaccines is urgently needed. In this study, we used the plasmid-based reverse genetics system (RGS) of BTV to rescue four recombinant viruses in which HA (influenza hemagglutinin) tags were inserted at different sites of VP2. In vitro, the recombinant tagged viruses exhibited morphologies, plaque, and growth kinetics similar to the parental BTV-16, and expressed both VP2 and HA tag. Subsequently, the selected recombinant tagged viruses were prepared as inactivated vaccines to immunize IFNAR(-/-) mice and sheep, and serological detection results of anti-HA antibody provided discriminative detection. In summary, we used plasmid-based RGS to rescue BTV recombinant viruses with HA tags inserted into VP2, and detected several sites on VP2 that can accommodate HA tags. Some of the recombinant tagged viruses have potential to be developed into distinctive inactivated vaccines.

A protective bivalent vaccine against Rift Valley fever and bluetongue

Rift Valley fever (RVF) and bluetongue (BT) are two important ruminant diseases transmitted by arthropods. Both viruses have shown important geographic spread leading to endemicity of BT virus (BTV) in Africa and Europe. In this work, we report a dual vaccine that simultaneously induces protective immune responses against BTV and RVFV based on modified vaccinia Ankara virus (MVA) expressing BTV proteins VP2, NS1, or a truncated form of NS1 (NS1-Nt), and RVFV Gn and Gc glycoproteins. IFNAR^(-/-) mice immunized with two doses of MVA-GnGc-VP2 developed a significant neutralizing antibody response against BTV-4 and RVFV. Furthermore, the homologous prime-boost immunization with MVA-GnGc-NS1 or MVA-GnGc-NS1-Nt triggered neutralizing antibodies against RVFV and NS1-specific cytotoxic CD8+ T cells in mice. Moreover, all mice immunized with MVA-GnGc-NS1 or MVA-GnGc-NS1-Nt remained healthy after lethal challenge with RVFV or BTV-4. The homologous prime-boost vaccination with MVA-GnGc-NS1, which was the best immunization strategy observed in mice, was assayed in sheep. Clinical signs and viremia were absent or highly reduced in vaccinated sheep after challenge with BTV-4 or RVFV. These results indicate that MVA-GnGc-NS1 vaccination elicits immune protection against RVFV and BTV in sheep.

Refined experimental design may increase the value of murine models for estimation of bluetongue virus virulence

Bluetongue is a serious non-contagious vector-borne viral disease in ruminants, causing poor animal welfare and economic consequences globally. Concern has been raised about the development of novel bluetongue virus (BTV) strains and their possibly altered virulence through the process of viral reassortment. Virulence is traditionally estimated in lethal dose 50 (LD₅₀) studies in murine models, but agreement with both in vitro and virulence in ruminants is questionable, and a refined experimental design is needed. Specific reassortants between wild-type and vaccine strains of BTV-1, -6 and -8 have previously been developed by reverse genetics. The aim of the present study was to rank the in vivo virulence of these parental and reassortant BTV strains by calculating LD₅₀ in a murine model by using an experimental design that is new to virology: a between-patient optimised three-level response surface pathway design. The inoculation procedure was intracranial. Fifteen suckling mice were used to establish LD₅₀ for each strain. Three parental and five reassortant virus strains were included. The LD₅₀s varied from of 0.1 (95% confidence interval (CI) 0-0.20) to 3.3 (95% CI 2.96-3.72) tissue culture infectious dose 50/ml. The results support the hypothesis that reassortment in BTV may lead to increased virulence in mice with potential negative consequences for the natural ruminant host. The ranking showed low agreement with in vitro properties and virulence in ruminants according to existing literature. Refined design such as response surface pathway design was found suitable for use in virology, and it introduces significant ethical and scientific improvements.

Virological, immunological and pathological findings of transplacentally transmitted bluetongue virus serotype 1 in IFNAR1-blocked mice during early and mid gestation

Transplacental transmission (TPT) of wild-type Indian BTV-1 had never been experimentally proved. This study was first time investigated TPT of Indian BTV-1 (isolated from aborted and stillborn goat fetal spleens). The sequential pathology, virological and immune cell kinetics (CD4⁺, CD8⁺ T-lymphocytes and NK cells in spleen and PBMCs), and apoptosis in IFNAR1-blocked pregnant mice during early (infected on 1 GD) and mid (infected on 8 GD) gestation have been studied. There was higher rate of TPT during mid stage (71.43%) than early (57.14%) stage. In early stage reduced implantation sites, early embryonic deaths, abortions, and necro-haemorrhagic lesions had observed. Mid stage, congenital defects and neurological lesions in foetuses like haemorrhages, diffuse cerebral edema, necrotizing encephalitis and decreased bone size (Alizarin red staining) were noticed. BTV-1 antigen was first time demonstrable in cells of mesometrium, decidua of embryos, placenta, uterus, ovary, and brain of foetuses by immunohistochemistry and quantified by real-time qRT-PCR. BTV-inoculated mice were seroconverted by 7 and 5 dpi, and reached peak levels by 15 and 9 dpi in early and mid gestation, respectively. CD4⁺ and CD8⁺ cells were significantly decreased (increased ratio) on 7 dpi but subsequently increased on 15 dpi in early gestation. In mid gestation, increased CD8⁺ cells (decreased ratio) were observed. Apoptotic cells in PBMCs and tissues increased during peak viral load. This first time TPT of wild-type Indian BTV-1 deserves to be reported for implementation of control strategies. This model will be very suitable for further research into mechanisms of TPT, overwintering, and vaccination strategies.

Attenuation of Bluetongue Virus (BTV) in an in ovo Model Is Related to the Changes of Viral Genetic Diversity of Cell-Culture Passaged BTV

The embryonated chicken egg (ECE) is routinely used for the laboratory isolation and adaptation of Bluetongue virus (BTV) in vitro. However, its utility as an alternate animal model has not been fully explored. In this paper, we evaluated the pathogenesis of BTV in ovo using a pathogenic isolate of South African BTV serotype 3 (BTV-3) derived from the blood of an infected sheep. Endothelio- and neurotropism of BTV-3 were observed by immunohistochemistry of non-structural protein 1 (NS1), NS3, NS3/3a, and viral protein 7 (VP7) antigens. In comparing the pathogenicity of BTV from infectious sheep blood with cell-culture-passaged BTV, including virus propagated through a Culicoides-derived cell line (KC) or ECE, we found virus attenuation in ECE following cell-culture passage. Genomic analysis of the consensus sequences of segments (Seg)-2, -5, -6, -7, -8, -9, and -10 identified several nucleotide and amino-acid mutations among the cell-culture-propagated BTV-3. Deep sequencing analysis revealed changes in BTV-3 genetic diversity in various genome segments, notably a reduction of Seg-7 diversity following passage in cell culture. Using this novel approach to investigate BTV pathogenicity in ovo, our findings support the notion that pathogenic BTV becomes attenuated in cell culture and that this change is associated with virus quasispecies evolution.

Modeling Arboviral Infection in Mice Lacking the Interferon Alpha/Beta Receptor

Arboviruses are arthropod-borne viruses that exhibit worldwide distribution and are a constant threat, not only for public health but also for wildlife, domestic animals, and even plants. To study disease pathogenesis and to develop efficient and safe therapies, the use of an appropriate animal model is a critical concern. Adult mice with gene knockouts of the interferon α/β (IFN-α/β) receptor (IFNAR(-/-)) have been described as a model of arbovirus infections. Studies with the natural hosts of these viruses are limited by financial and ethical issues, and in some cases, the need to have facilities with a biosafety level 3 with sufficient space to accommodate large animals. Moreover, the number of animals in the experiments must provide results with statistical significance. Recent advances in animal models in the last decade among other gaps in knowledge have contributed to the better understanding of arbovirus infections. A tremendous advantage of the IFNAR(-/-) mouse model is the availability of a wide variety of reagents that can be used to study many aspects of the immune response to the virus. Although extrapolation of findings in mice to natural hosts must be done with care due to differences in the biology between mouse and humans, experimental infections of IFNAR(-/-) mice with several studied arboviruses closely mimics hallmarks of these viruses in their natural host. Therefore, IFNAR(-/-) mice are a good model to facilitate studies on arbovirus transmission, pathogenesis, virulence, and the protective efficacy of new vaccines. In this review article, the most important arboviruses that have been studied using the IFNAR(-/-) mouse model will be reviewed.

CD8 T Cell Responses to an Immunodominant Epitope within the Nonstructural Protein NS1 Provide Wide Immunoprotection against Bluetongue Virus in IFNAR-/- Mice

Conventional vaccines have controlled or limited BTV expansion in the past, but they cannot address the need for cross-protection among serotypes and do not allow distinguishing between infected and vaccinated animals (DIVA strategy). There is a need to develop universal vaccines that induce effective protection against multiple BTV serotypes. In this work we have shown the importance of the nonstructural protein NS1, conserved among all the BTV serotypes, in CD8 T cell-mediated protection against multiple BTV serotypes when vectorized as a recombinant MVA vaccine.

The development of vaccines against bluetongue, a prevalent livestock disease, has been focused on surface antigens that induce strong neutralizing antibody responses. Because of their antigenic variability, these vaccines are usually serotype restricted. We now show that a single highly conserved nonstructural protein, NS1, expressed in a modified vaccinia Ankara virus (MVA) vector can provide multiserotype protection in IFNAR^−/− 129 mice against bluetongue virus (BTV) that is largely dependent on CD8 T cell responses. We found that the protective antigenic capacity of NS1 resides within the N terminus of the protein and is provided in the absence of neutralizing antibodies. The protective CD8 T cell response requires the presence of a specific peptide within the N terminus of NS1, since its deletion ablates the efficacy of the vaccine formulation. These data reveal the importance of the nonstructural protein NS1 in CD8 T cell-mediated protection against multiple BTV serotypes when vectorized as a recombinant MVA vaccine.

IMPORTANCE Conventional vaccines have controlled or limited BTV expansion in the past, but they cannot address the need for cross-protection among serotypes and do not allow distinguishing between infected and vaccinated animals (DIVA strategy). There is a need to develop universal vaccines that induce effective protection against multiple BTV serotypes. In this work we have shown the importance of the nonstructural protein NS1, conserved among all the BTV serotypes, in CD8 T cell-mediated protection against multiple BTV serotypes when vectorized as a recombinant MVA vaccine.

Nucleocapsid protein-based vaccine provides protection in mice against lethal Crimean-Congo hemorrhagic fever virus challenge

Crimean-Congo hemorrhagic fever (CCHF) is an acute, often fatal viral disease characterized by rapid onset of febrile symptoms followed by hemorrhagic manifestations. The etiologic agent, CCHF orthonairovirus (CCHFV), can infect several mammals in nature but only seems to cause clinical disease in humans. Over the past two decades there has been an increase in total number of CCHF case reports, including imported CCHF patients, and an expansion of CCHF endemic areas. Despite its increased public health burden there are currently no licensed vaccines or treatments to prevent CCHF. We here report the development and assessment of the protective efficacy of an adenovirus (Ad)-based vaccine expressing the nucleocapsid protein (N) of CCHFV (Ad-N) in a lethal immunocompromised mouse model of CCHF. The results show that Ad-N can protect mice from CCHF mortality and that this platform should be considered for future CCHFV vaccine strategies.

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease that can manifest as a viral hemorrhagic fever syndrome. The CCHF virus is widely spread throughout the African continent, the Balkans, the Middle East, Southern Russia and Western Asia where it remains a serious public health concern. Currently, there are no licensed treatments or vaccines available, and medical countermeasures are urgently needed. We developed an adenovirus vector vaccine based on the conserved structural nucleoprotein (N) as the antigen. A prime-boost approach showed promising efficacy in the most widely used immunocompromised mouse model. This vaccine approach demonstrates a role for N in protection and suggests its consideration for future CCHFV vaccine strategies.

Recall T cell responses to bluetongue virus produce a narrowing of the T cell repertoire

In most viral infections, recall T cell responses are critical for protection. The magnitude of these secondary responses can also affect the CD8 and CD4 epitope repertoire diversity. Bluetongue virus (BTV) infection in sheep elicits a T cell response that contributes to viremia control and could be relevant for cross-protection between BTV serotypes. Here, we characterized CD4⁺ and CD8⁺ T cell responses during primary and recall responses. During primary immune responses, both CD4⁺ and CD8⁺ T cell populations expanded by 14 days post-infection (dpi). CD4⁺ T cell populations showed a lower peak of expansion and prolonged contraction phase compared to CD8⁺ T cell populations. Recall responses to BTV challenge led to BTV-specific expansion and activation of CD8⁺ but not of CD4⁺ T cells. The evolution of the BTV-specific TCR repertoire was also characterized in response to VP7 peptide stimulation. Striking differences in repertoire development were noted over the time-course of infection. During primary responses, a broader repertoire was induced for MHC-I and MHC-II epitopes. However, during memory responses, a narrowed repertoire was activated towards a dominant motif in VP7 comprising amino acids 139–291. Monocytes were also examined, and expanded during acute infection resolution. In addition, pro-inflammatory cytokine levels increased after BTV inoculation and persisted throughout the experiment, indicative of a prolonged inflammatory state during BTV infections. These findings could have implications for vaccine design as the narrowing memory T cell repertoire induced after BTV re-infection could lead to the development of protective immunodominant TCR repertoires that differs between individual sheep.

A review of potential bluetongue virus vaccine strategies

Bluetongue (BT) is an economically important, non-zoonotic arboviral disease of certain wild and domestic species of cloven-hooved ungulates. Bluetongue virus (BTV) is the causative agent and the occurrence of BTV infection is distinctly seasonal in temperate regions of the world, and dependent on the presence of vector biting midges (e.g. Culicoides sonorensis in much of North America). In recent years, severe outbreaks have occurred throughout Europe and BTV is endemic in most tropical and temperate regions of the world. Several vaccines have been licensed for commercial use, including modified live (live-attenuated) and inactivated products, and this review summarizes recent strategies developed for BTV vaccines with emphasis on technologies suitable for differentiating naturally infected from vaccinated animals. The goal of this review is to evaluate realistic vaccine strategies that might be utilized to control or prevent future outbreaks of BT.

Pathological Characterization Of IFNAR(-/-) Mice Infected With Bluetongue Virus Serotype 4

Bluetongue virus (BTV) replicates in lymphoid tissues where infected mononuclear leukocytes secrete proinflammatory and vasoactive mediators that can contribute to bluetongue (BT) pathogenesis. Using the well-characterized IFNAR(-/-) mice animal model, we have now studied the histopathology and dynamics of leukocyte populations in different target tissues (spleen, thymus, and lung) during BTV-4 infection by histological and immunohistochemical techniques. The spleen and thymus of BTV-4 infected mice showed severe lymphoid depletion on H&E stained sections. This finding was confirmed by IHC, showing moderate decreased immunopositivity against CD3 in the thymus, and scarce immunoreactivity against CD3 and CD79 in the rest of the white pulp in the spleen, together with an increase in MAC387 immunostaining. BTV-4 infection also induced the expression of active caspase-3 in the spleen, where apoptotic debris was observed by H&E. A dramatic increase in iNOS immunoreactivity associated to necrotic areas of the white pulp was observed, being less noticeable in the thymus and the lung. The induction of pro-inflammatory cytokines in tissues where BTV replicates was evaluated by measuring transcript levels by RT-qPCR. BTV-4 infection led to enhance transcription of IFN-γ, TNF, IL-6, IL-12-p40, and IL-1β mRNA in the thymus, spleen and lung, correlating with the level of virus replication in these tissues. Disease progression and pathogenesis in IFNAR(-/-) mice closely mimics hallmarks of bluetongue disease in ruminants. IFNAR(-/-) mice are a good choice to facilitate a faster advance in the field of orbiviruses.

Defeating Bluetongue virus: new approaches in the development of multiserotype vaccines

Bluetongue virus (BTV) is a global threat to domestic and wild ruminants, causing massive economic losses throughout the world. New serotypes of the virus are rapidly emerging in different continents, unfortunately there is little cross-protection between BTV serotypes. The eradication of the virus from a region is particularly complicated in areas where multiple serotypes circulate for a long time. The present review summarizes the actual concerns about the spread of the virus and relevant approaches to develop efficient vaccines against BTV, in particular those focused on a multiserotype design.

A Review of Knowledge Gaps and Tools for Orbivirus Research

Although recognized as causing emerging and re-emerging disease outbreaks worldwide since the late 1800 s, there has been growing interest in the United States and Europe in recent years in orbiviruses, their insect vectors, and the diseases they cause in domestic livestock and wildlife. This is due, in part, to the emergence of bluetongue (BT) in northern Europe in 2006-2007 resulting in a devastating outbreak, as well as severe BT outbreaks in sheep and epizootic hemorrhagic disease (EHD) outbreaks in deer and cattle in the United States. Of notable concern is the isolation of as many as 10 new BT virus (BTV) serotypes in the United States since 1999 and their associated unknowns, such as route of introduction, virulence to mammals, and indigenous competent vectors. This review, based on a gap analysis workshop composed of international experts on orbiviruses conducted in 2013, gives a global perspective of current basic virological understanding of orbiviruses, with particular attention to BTV and the closely related epizootic hemorrhagic disease virus (EHDV), and identifies a multitude of basic virology research gaps, critical for predicting and preventing outbreaks.

Identification of CD8 T cell epitopes in VP2 and NS1 proteins of African horse sickness virus in IFNAR(-/-) mice

African horse sickness virus (AHSV) is an Orbivirus of the family Reoviridae that causes severe pathology in equids. Previous work in our laboratory showed the presence of AHSV-specific CD8(+) T cells in mice immunized with recombinant Modified Vaccinia Ankara (rMVA) expressing VP2 and NS1 proteins. In the present work, we selected potential CD8 T cell epitopes (MHC-class I binding peptides) for the 129 mouse strain from the VP2 and NS1 proteins of AHSV-4, using a combination of four epitope prediction algorithms (SYFPEITHI, BYMAS, NetMHC I and NetMHCpan). ELISPOT and Intracellular Cytokine Staining (ICS) analysis showed that the VP2-720 (MSLLNFGAV), VP2-1044 (YTFGNKFLL), and NS1-83 (CVIKNADYV) peptides elicited IFN-γ production in splenocytes of MVA-VP2 and MVA-NS1 immunized mice and were identified as CD8(+) T cell epitopes. In addition, these three MHC-class I-binding peptides induced the expression of CD107a in CD8(+) T cells, an indirect marker of cytotoxic activity. Importantly, VP2-1044 and NS1-83 epitopes are conserved among all nine AHSV serotypes. These data demonstrate the activation of AHSV specific T-cell epitopes during vaccination with rMVAs expressing VP2 and NS1. Furthermore, the characterization of these CD8(+) T-cell epitopes provides information useful for the design of novel marker multiserotype vaccines against AHSV.

Protective Efficacy in Sheep of Adenovirus-Vectored Vaccines against Bluetongue Virus Is Associated with Specific T Cell Responses

Bluetongue virus (BTV) is an economically important Orbivirus of the Reoviridae family that causes a hemorrhagic disease in ruminants. Its control has been achieved by inactivated-vaccines that have proven to protect against homologous BTV challenge although unable to induce long-term immunity. Therefore, a more efficient control strategy needs to be developed. Recombinant adenovirus vectors are lead vaccine candidates for protection of several diseases, mainly because of their potency to induce potent T cell immunity. Here we report the induction of humoral and T-cell mediated responses able to protect animals against BTV challenge by recombinant replication-defective human adenovirus serotype 5 (Ad5) expressing either VP7, VP2 or NS3 BTV proteins. First we used the IFNAR(-/-) mouse model system to establish a proof of principle, and afterwards we assayed the protective efficacy in sheep, the natural host of BTV. Mice were completely protected against BTV challenge, developing humoral and BTV-specific CD8+- and CD4+-T cell responses by vaccination with the different rAd5. Sheep vaccinated with Ad5-BTV-VP2 and Ad5-BTV-VP7 or only with Ad5-BTV-VP7 and challenged with BTV showed mild disease symptoms and reduced viremia. This partial protection was achieved in the absence of neutralizing antibodies but strong BTV-specific CD8+ T cell responses in those sheep vaccinated with Ad5-BTV-VP7. These data indicate that rAd5 is a suitable vaccine vector to induce T cell immunity during BTV vaccination and provide new data regarding the relevance of T cell responses in protection during BTV infection.

Re-Emergence of Bluetongue Virus Serotype 8 in France, 2015

At the end of August 2015, a ram located in central France (department of Allier) showed clinical signs suggestive of BTV (Bluetongue virus) infection. However, none of the other animals located in the herd showed any signs of the Bluetongue disease. Laboratory analyses identified the virus as BTV serotype 8. The viro and sero prevalence intraherd were 2.4% and 8.6% in sheep and 18.3% and 42.9% in cattle, respectively. Phylogenetic studies showed that the sequences of this strain are closely related to another BTV-8 strain that has circulated in France in 2006-2008. The origin of the outbreak is unclear but it may be assumed that the BTV-8 has probably circulated at very low prevalence (possibly in livestock or wildlife) since its first emergence in 2007-2008.

Characterization of a second open reading frame in genome segment 10 of bluetongue virus

Viruses have often evolved overlapping reading frames in order to maximize their coding capacity. Until recently, the segmented dsRNA genome of viruses of the Orbivirus genus was thought to be monocistronic, but the identification of the bluetongue virus (BTV) NS4 protein changed this assumption. A small ORF in segment 10, overlapping the NS3 ORF in the +1 position, is maintained in more than 300 strains of the 27 different BTV serotypes and in more than 200 strains of the phylogenetically related African horse sickness virus (AHSV). In BTV, this ORF (named S10-ORF2 in this study) encodes a putative protein 50–59 residues in length and appears to be under strong positive selection. HA- or GFP-tagged versions of S10-ORF2 expressed from transfected plasmids localized within the nucleoli of transfected cells, unless a putative nucleolar localization signal was mutated. S10-ORF2 inhibited gene expression, but not RNA translation, in transient transfection reporter assays. In both mammalian and insect cells, BTV S10-ORF2 deletion mutants (BTV8ΔS10-ORF2) displayed similar replication kinetics to wt virus. In vivo, S10-ORF2 deletion mutants were pathogenic in mouse models of disease. Although further evidence is required for S10-ORF2 expression during infection, the data presented provide an initial characterization of this ORF.

Turnover Rate of NS3 Proteins Modulates Bluetongue Virus Replication Kinetics in a Host-Specific Manner

Bluetongue virus (BTV) is an arbovirus transmitted to livestock by midges of the Culicoides family and is the etiological agent of a hemorrhagic disease in sheep and other ruminants. In mammalian cells, BTV particles are released primarily by virus-induced cell lysis, while in insect cells they bud from the plasma membrane and establish a persistent infection. BTV possesses a ten-segmented double-stranded RNA genome, and NS3 proteins are encoded by segment 10 (Seg-10). The viral nonstructural protein 3 (NS3) plays a key role in mediating BTV egress as well as in impeding the in vitro synthesis of type I interferon in mammalian cells. In this study, we asked whether genetically distant NS3 proteins can alter BTV-host interactions. Using a reverse genetics approach, we showed that, depending on the NS3 considered, BTV replication kinetics varied in mammals but not in insects. In particular, one of the NS3 proteins analyzed harbored a proline at position 24 that leads to its rapid intracellular decay in ovine but not in Culicoides cells and to the attenuation of BTV virulence in a mouse model of disease. Overall, our data reveal that the genetic variability of Seg-10/NS3 differentially modulates BTV replication kinetics in a host-specific manner and highlight the role of the host-specific variation in NS3 protein turnover rate.

IMPORTANCE

BTV is the causative agent of a severe disease transmitted between ruminants by biting midges of Culicoides species. NS3, encoded by Seg-10 of the BTV genome, fulfills key roles in BTV infection. As Seg-10 sequences from various BTV strains display genetic variability, we assessed the impact of different Seg-10 and NS3 proteins on BTV infection and host interactions. In this study, we revealed that various Seg-10/NS3 proteins alter BTV replication kinetics in mammals but not in insects. Notably, we found that NS3 protein turnover may vary in ovine but not in Culicoides cells due to a single amino acid residue that, most likely, leads to rapid and host-dependent protein degradation. Overall, this study highlights that genetically distant BTV Seg-10/NS3 influence BTV biological properties in a host-specific manner and increases our understanding of how NS3 proteins contribute to the outcome of BTV infection.

Immunization of knock-out α/β interferon receptor mice against high lethal dose of Crimean-Congo hemorrhagic fever virus with a cell culture based vaccine

Crimean-Congo hemorrhagic fever (CCHF) is an acute tick-borne zoonotic disease. The disease has been reported in many countries of Africa, Asia, the Middle East, and in Eurasia. During the past decade, new foci of CCHF have emerged in the Balkan Peninsula, southwest Russia, the Middle East, western China, India, Africa, and Turkey. CCHF virus produces severe hemorrhagic manifestations in humans with fatality rates up to 30%. Vaccine development efforts have been significantly hampered by a lack of animal models and therefore, no protective vaccine has been achieved. Lately, IFN α/β receptor deficient (IFNAR^−/−) mice have been established as a novel small animal model of CCHF virus infection. In the present study, we found that IFNAR^−/− mice highly susceptible to CCHF virus Turkey-Kelkit06 strain. Immunization with the cell culture based vaccine elicited a significant level of protection against high dose challenge (1,000 PPFU) with a homologous CCHF virus in IFNAR^−/− mice.

The CCHF virus is one of the most geographically widespread tick-borne viruses, and has been reported in many countries of Africa, Asia, the Middle East, and in Eurasia. Since 2002, there have been more than 8000 cases in Turkey, with mortality rate around 5%, making CCHF a public health concern. There are currently no specific antiviral therapies or licensed vaccines for CCHF. Due to limitations in treatment options and difficulties posed by vector control vaccination remains the most logical method of disease control. In the present study, we showed that immunization with the cell culture based vaccine against CCHF elicited a significant level of protection against a high dose challenge (1,000 PPFU) with a homologous CCHF virus Turkey-Kelkit06 strain in IFNAR^−/− mice. The animals vaccinated with 5, 20, 40 μg dose of the cell culture based vaccine were partially protected (60%, 80% and 80% protection, respectively) with a significant delay in time to death. Neutralizing antibody responses are essential for the increased of protection in the mice vaccinated with the cell culture based vaccine but this cannot be the only mechanism of protection.

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.

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.

Ovine and murine T cell epitopes from the non-structural protein 1 (NS1) of bluetongue virus serotype 8 (BTV-8) are shared among viral serotypes

Bluetongue virus (BTV) is a non-enveloped dsRNA virus that causes a haemorrhagic disease mainly in sheep. It is an economically important Orbivirus of the Reoviridae family. In order to estimate the importance of T cell responses during BTV infection, it is essential to identify the epitopes targeted by the immune system. In the present work, we selected potential T cell epitopes (3 MHC-class II-binding and 8 MHC-class I binding peptides) for the C57BL/6 mouse strain from the BTV-8 non-structural protein NS1, using H2^b-binding predictive algorithms. Peptide binding assays confirmed all MHC-class I predicted peptides bound MHC-class I molecules. The immunogenicity of these 11 predicted peptides was then determined using splenocytes from BTV-8-inoculated C57BL/6 mice. Four MHC-class I binding peptides elicited specific IFN-γ production and generated cytotoxic T lymphocytes (CTL) in BTV-8 infected mice. CTL specific for 2 of these peptides were also able to recognise target cells infected with different BTV serotypes. Similarly, using a combination of IFN-γ ELISPOT, intracellular cytokine staining and proliferation assays, two MHC-class II peptides were identified as CD4⁺ T cell epitopes in BTV-8 infected mice. Importantly, two peptides were also consistently immunogenic in sheep infected with BTV-8 using IFN-γ ELISPOT assays. Both of these peptides stimulated CD4⁺ T cells that cross-reacted with other BTV serotypes. The characterisation of these T cell epitopes can help develop vaccines protecting against a broad spectrum of BTV serotypes and differentiate infected from vaccinated animals.

A review of experimental infections with bluetongue virus in the mammalian host

Experimental infection studies with bluetongue virus (BTV) in the mammalian host have a history that stretches back to the late 18th century. Studies in a wide range of ruminant and camelid species as well as mice have been instrumental in understanding BTV transmission, bluetongue (BT) pathogenicity/pathogenesis, viral virulence, the induced immune response, as well as reproductive failures associated with BTV infection. These studies have in many cases been complemented by in vitro studies with BTV in different cell types in tissue culture. Together these studies have formed the basis for the understanding of BTV-host interaction and have contributed to the design of successful control strategies, including the development of effective vaccines. This review describes some of the fundamental and contemporary infection studies that have been conducted with BTV in the mammalian host and provides an overview of the principal animal welfare issues that should be considered when designing experimental infection studies with BTV in in vivo infection models. Examples are provided from the authors' own laboratory where the three Rs (replacement, reduction and refinement) have been implemented in the design of experimental infection studies with BTV in mice and goats. The use of the ARRIVE guidelines for the reporting of data from animal infection studies is emphasized.

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.

Recombinant vaccines against bluetongue virus

Bluetongue (BT) is a hemorrhagic disease of ruminants caused by bluetongue virus (BTV), the prototype member of the genus Orbivirus within the family Reoviridae and is transmitted via biting midges of the genus Culicoides. BTV can be found on all continents except Antarctica, and up to 26 immunologically distinct BTV serotypes have been identified. Live attenuated and inactivated BTV vaccines have been used over the years with different degrees of success. The multiple outbreaks of BTV in Mediterranean Europe in the last two decades and the incursion of BTV-8 in Northern Europe in 2008 has re-stimulated the interest to develop improved vaccination strategies against BTV. In particular, safer, cross-reactive, more efficacious vaccines with differential diagnostic capability have been pursued by multiple BTV research groups and vaccine manufacturers. A wide variety of recombinant BTV vaccine prototypes have been investigated, ranging from baculovirus-expressed sub-unit vaccines to the use of live viral vectors. This article gives a brief overview of all these modern approaches to develop vaccines against BTV including some recent unpublished data.

Induction and control of the type I interferon pathway by Bluetongue virus

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A general review describing the current knowledge on the type I IFN pathway.

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Description of several mechanisms evolved by viruses to counteract this antiviral response.

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An up-to-date review on the interaction of BTV and the type I IFN pathway in vivo and in vitro.

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Description of the cellular sensors involved in the induction of IFN-α/β synthesis upon BTV infection in haematopoietic and non-haematopoietic cells.

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Description of the strategies evolved by BTV to counteract this cellular antiviral response.

The innate immune response is the first line of defence against viruses, involving the production of type I IFN (IFN-α/β) and other pro-inflammatory cytokines that control the infection. It also shapes the adaptive immune response generated by both T and B cells. Production of type I IFN occurs both in vivo and in vitro in response to Bluetongue virus (BTV), an arthropod-borne virus. However, the mechanisms responsible for the production of IFN-β in response to BTV remained unknown until recently and are still not completely understood. In this review, we describe the recent advances in the identification of cellular sensors and signalling pathways involved in this process. The RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) were shown to be involved in the expression of IFN-β as well as in the control of BTV infection in non-haematopoietic cells. In contrast, induction of IFN-α/β synthesis in sheep primary plasmacytoid dendritic cells (pDCs) required the MyD88 adaptor independently of the Toll-like receptor 7 (TLR7), as well as the kinases dsRNA-activated protein kinase (PKR) and stress-activated protein kinase (SAPK)/Jun N-terminal protein kinase (JNK). As type I IFN is essential for the establishment of an antiviral cellular response, most of viruses have elaborated counteracting mechanisms to hinder its action. This review also addresses the ability of BTV to interfere with IFN-β synthesis and the recent findings describing the non-structural viral protein NS3 as a powerful antagonist of the host cellular response.

Type I interferon limits the capacity of bluetongue virus to infect hematopoietic precursors and dendritic cells in vitro and in vivo

Hematopoietic stem cells (HSCs) give rise to progenitors with potential to produce multiple cell types, including dendritic cells (DCs). DCs are the principal antigen-presenting cells and represent the crucial link between innate and adaptive immune responses. Bluetongue virus (BTV), an economically important Orbivirus of the Reoviridae family, causes a hemorrhagic disease mainly in sheep and occasionally in other species of ruminants. BTV is transmitted between its mammalian hosts by certain species of biting midges (Culicoides spp.) and is a potent alpha interferon (IFN-α) inducer. In the present report, we show that BTV infects cells of hematopoietic origin but not HSCs in immunocompetent sheep. However, BTV infects HSCs in the absence of type I IFN (IFN-I) signaling in vitro and in vivo. Infection of HSCs in vitro results in cellular death by apoptosis. Furthermore, BTV infects bone marrow-derived DCs (BM-DCs), interfering with their development to mature DCs in the absence of type I IFN signaling. Costimulatory molecules CD80 and CD86 and costimulatory molecules CD40 and major histocompatibility complex class II (MHC-II) are affected by BTV infection, suggesting that BTV interferes with DC antigen-presenting capacity. In vivo, different DC populations are also affected during the course of infection, probably as a result of a direct effect of BTV replication in DCs and the production of infectious virus. These new findings suggest that BTV infection of HSCs and DCs can impair the immune response, leading to persistence or animal death, and that this relies on IFN-I.

Interferon α/β receptor knockout mice as a model to study bluetongue virus infection

Bluetongue is an arthropod-borne disease caused by a virus of the genus Orbivirus, the bluetongue virus (BTV), which affects ruminant livestock such as cattle, sheep, and goats and wild ruminants such as deer, and camelids. Recently, adult mice with gene knockouts of the interferon α/β receptor (IFNAR-/-) have been described as a model of lethal BTV infection. IFNAR(-/-) mice are highly susceptible to BTV-1, BTV-4 and BTV-8 infection when the virus is administered intravenously or subcutaneosuly. Disease progression and pathogenesis closely mimics signs of bluetongue disease in ruminants. In the present paper we review the studies where IFNAR(-/-) mice have been used as an animal model to study BTV transmission, pathogenesis, virulence, and protective efficacy of inactivated and new recombinant marker BTV vaccines. Furthermore, we report new data on protective efficacy of different strategies of BTV vaccination and also on induction of interferon α/β and proinflammatory immune responses in IFNAR(-/-) mice infected with BTV.

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.