Bluetongue virus serotype 8 virus-like particles protect sheep against virulent virus infection as a single or multi-serotype cocktail immunogen

Multi-Gene Recombinant Baculovirus Expression Systems: From Inception to Contemporary Applications

Many protein expression systems are primarily utilised to produce a single, specific recombinant protein. In contrast, most biological processes such as virus assembly rely upon a complex of several interacting proteins rather than the activity of a sole protein. The high complexity of the baculovirus genome, coupled with a multiphase replication cycle incorporating distinct transcriptional steps, made it the ideal system to manipulate for high-level expression of a single, or co-expression of multiple, foreign proteins within a single cell. We have developed and utilised a series of recombinant baculovirus systems to unravel the sequential assembly process of a complex non-enveloped model virus, bluetongue virus (BTV). The high protein yields expressed by the baculovirus system not only facilitated structure-function analysis of each viral protein but were also advantageous to crystallography studies and supported the first atomic-level resolution of a recombinant viral protein, the major BTV capsid protein. Further, the formation of recombinant double-shelled virus-like particles (VLPs) provided insights into the structure-function relationships among the four major structural proteins of the BTV whilst also representing a potential candidate for a viral vaccine. The baculovirus multi-gene expression system facilitated the study of structurally complex viruses (both non-enveloped and enveloped viruses) and heralded a new generation of viral vaccines.

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.

Recent Development of Ruminant Vaccine Against Viral Diseases

Pathogens of viral origin produce a large variety of infectious diseases in livestock. It is essential to establish the best practices in animal care and an efficient way to stop and prevent infectious diseases that impact animal husbandry. So far, the greatest way to combat the disease is to adopt a vaccine policy. In the fight against infectious diseases, vaccines are very popular. Vaccination's fundamental concept is to utilize particular antigens, either endogenous or exogenous to induce immunity against the antigens or cells. In light of how past emerging and reemerging infectious diseases and pandemics were handled, examining the vaccination methods and technological platforms utilized for the animals may provide some useful insights. New vaccine manufacturing methods have evolved because of developments in technology and medicine and our broad knowledge of immunology, molecular biology, microbiology, and biochemistry, among other basic science disciplines. Genetic engineering, proteomics, and other advanced technologies have aided in implementing novel vaccine theories, resulting in the discovery of new ruminant vaccines and the improvement of existing ones. Subunit vaccines, recombinant vaccines, DNA vaccines, and vectored vaccines are increasingly gaining scientific and public attention as the next generation of vaccines and are being seen as viable replacements to conventional vaccines. The current review looks at the effects and implications of recent ruminant vaccine advances in terms of evolving microbiology, immunology, and molecular biology.

The Mink Circovirus Capsid Subunit Expressed by Recombinant Baculovirus Protects Minks against Refractory Diarrhea in Field

Mink refractory diarrhea is a seasonal disease that occurs in many mink farms in China. Mink circovirus (MiCV) has been recognized as the causative agent of the disease. The aim of the study was to develop a subunit vaccine against mink refractory diarrhea. A recombinant baculovirus strain expressing the capsid protein was constructed using the baculovirus expression vector system (BEVS). A subunit vaccine was developed based on the capsid protein with appropriate adjuvant. Then, a field trial was carried out in two districts in order to evaluate the efficiency of the subunit vaccine. The field trial indicated that in total, only 1.8% of the minks developed typical diarrhea in the vaccinated group compared with 74.5% in the control group. The vaccination could significantly reduce the infection rate of MiCV among the mink herds and could restrain the virus' shedding from feces. Furthermore, the vaccinated group had a higher average litter size in the following year compared to the control group. Collectively, the results indicated that the subunit vaccine based on the capsid protein can provide reliable protection against MiCV infection.

Potential of Using Capripoxvirus Vectored Vaccines Against Arboviruses in Sheep, Goats, and Cattle

The genus capripoxvirus consists of sheeppox virus, goatpox virus, and lumpy skin disease virus, which affect sheep, goats, and cattle, respectively. Together capripoxviruses cause significant economic losses to the sheep, goat, and cattle industry where these diseases are present. These diseases have spread into previously free bordering regions most recently demonstrated with the spread of lumpy skin disease virus into the Middle East, some Eastern European countries, and Russia. This recent spread has highlighted the transboundary nature of these diseases. To control lumpy skin disease virus, live attenuated viral vaccines are used in endemic countries as well as in response to an outbreak. For sheeppox and goatpox, live attenuated viral vaccines are used in endemic countries; these diseases can also be contained through slaughter of infected animals to stamp out the disease. The thermostability, narrow host range, and ability of capripoxviruses to express a wide variety of antigens make capripoxviruses ideal vectors. The ability to immunize animals against multiple diseases simultaneously increases vaccination efficiency by decreasing the number of vaccinations required. Additionally, the use of capripoxvirus vectored vaccines allows the possibility of differentiating infected from vaccinated animals. Arboviruses such as bluetongue virus and Rift Valley fever viruses are also responsible for significant economic losses in endemic countries. In the case of Rift Valley fever virus, vaccination is not routinely practiced unless there is an outbreak making vaccination not as effective, therefore, incorporating Rift Valley fever vaccination into routine capripoxvirus vaccination would be highly beneficial. This review will discuss the potential of using capripoxvirus as a vector expressing protective arboviral antigens.

Plant-produced chimeric virus-like particles - a new generation vaccine against African horse sickness

BACKGROUND

African horse sickness (AHS) is a severe arthropod-borne viral disease of equids, with a mortality rate of up to 95% in susceptible naïve horses. Due to safety concerns with the current live, attenuated AHS vaccine, alternate safe and effective vaccination strategies such as virus-like particles (VLPs) are being investigated. Transient plant-based expression systems are a rapid and highly scalable means of producing such African horse sickness virus (AHSV) VLPs for vaccine purposes.

RESULTS

In this study, we demonstrated that transient co-expression of the four AHSV capsid proteins in agroinfiltrated Nicotiana benthamiana dXT/FT plants not only allowed for the assembly of homogenous AHSV-1 VLPs but also single, double and triple chimeric VLPs, where one capsid protein originated from one AHS serotype and at least one other capsid protein originated from another AHS serotype. Following optimisation of a large scale VLP purification procedure, the safety and immunogenicity of the plant-produced, triple chimeric AHSV-6 VLPs was confirmed in horses, the target species.

CONCLUSIONS

We have successfully shown assembly of single and double chimeric AHSV-7 VLPs, as well as triple chimeric AHSV-6 VLPs, in Nicotiana benthamiana dXT/FT plants. Plant produced chimeric AHSV-6 VLPs were found to be safe for administration into 6 month old foals as well as capable of eliciting a weak neutralizing humoral immune response in these target animals against homologous AHSV virus.

Prospects of Next-Generation Vaccines for Bluetongue

Bluetongue (BT) is a haemorrhagic disease of wild and domestic ruminants with a huge economic worldwide impact on livestock. The disease is caused by BT-virus transmitted by Culicoides biting midges and disease control without vaccination is hardly possible. Vaccination is the most feasible and cost-effective way to minimize economic losses. Marketed BT vaccines are successfully used in different parts of the world. Inactivated BT vaccines are efficacious and safe but relatively expensive, whereas live-attenuated vaccines are efficacious and cheap but are unsafe because of under-attenuation, onward spread, reversion to virulence, and reassortment events. Both manufactured BT vaccines do not enable differentiating infected from vaccinated animals (DIVA) and protection is limited to the respective serotype. The ideal BT vaccine is a licensed, affordable, completely safe DIVA vaccine, that induces quick, lifelong, broad protection in all susceptible ruminant species. Promising vaccine candidates show improvement for one or more of these main vaccine standards. BTV protein vaccines and viral vector vaccines have DIVA potential depending on the selected BTV antigens, but are less effective and likely more costly per protected animal than current vaccines. Several vaccine platforms based on replicating BTV are applied for many serotypes by exchange of serotype dominant outer shell proteins. These platforms based on one BTV backbone result in attenuation or abortive virus replication and prevent disease by and spread of vaccine virus as well as reversion to virulence. These replicating BT vaccines induce humoral and T-cell mediated immune responses to all viral proteins except to one, which could enable DIVA tests. Most of these replicating vaccines can be produced similarly as currently marketed BT vaccines. All replicating vaccine platforms developed by reverse genetics are classified as genetic modified organisms. This implies extensive and expensive safety trails in target ruminant species, and acceptance by the community could be hindered. Nonetheless, several experimental BT vaccines show very promising improvements and could compete with marketed vaccines regarding their vaccine profile, but none of these next generation BT vaccines have been licensed yet.

Elicitation of Th1/Th2 related responses in mice by chitosan nanoparticles loaded with Brucella abortus malate dehydrogenase, outer membrane proteins 10 and 19

Brucella spp. is the causative agent of brucellosis, one of the worldwide diseases. The pathogen infects humans and animals mainly through the digestive or respiratory tract. Therefore, induction of mucosal immunity is required as the first line of defense. In this study, three Brucella abortus recombinant proteins, malate dehydrogenase (rMdh), outer membrane proteins (rOmp) 10 and 19 were loaded in mucoadhesive chitosan nanoparticles (CNs) and induction of mucosal and systemic immunity were investigated after intranasal immunization of BALB/c mice. These antigens were also coimmunized as cocktail (rCocktail) to evaluate multiple antigen specific vaccine candidates. At 6-weeks post-immunization (wpi), antigen specific total IgG was increased in all of the immunized groups, predominantly IgG1. In addition, spleenocyte from rMdh-, rOmp19-, and rCocktail-immunized groups significantly produced IFN-γ and IL-4 suggesting the induction of a mixed Th1-Th2 response. For mucosal immunity, anti-Mdh IgA from nasal washes and fecal excretions, and anti-Omps IgA from sera, nasal washes, genital secretions and fecal excretions were significantly increased in single antigen immunized groups. In the rCocktail-immunized group, anti-Mdh IgA were significantly increased while anti-Omps IgA was not. Collectively, this study indicates that comprise of B. abortus antigen-loaded CNs elicited the antigen-specific IgA with a Th2-polarized immune responses and combination of the highly immunogenic antigens elicited IgG specific to each type of antigen.

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.

Bluetongue virus serotype 27: Experimental infection of goats, sheep and cattle with three BTV-27 variants reveal atypical characteristics and likely direct contact transmission BTV-27 between goats

Bluetongue virus (BTV) hitherto consisted of 26 recognized serotypes, of which all except BTV-26 are primarily transmitted by certain species of Culicoides biting midges. Three variants of an additional 27th bluetongue virus serotype (BTV-27v01-v03) were recently detected in asymptomatic goats in Corsica, France, 2014-2015. Molecular characterization revealed genetic differences between the three variants. Therefore, in vivo characteristics were investigated by experimental infection of a total of 15 goats, 11 sheep and 4 cattle with any one of the three variants in separated animal trials. In goat trials, BTV-naïve animals of the same species were kept in a facility where direct contact was unhindered. Of the 15 inoculated goats, 13 and 14 animals were found positive for BTV-RNA and antibodies (Ab), respectively, until the end of the experiments. Surprisingly, BTV-Ab levels as measured with ELISA and neutralization test (SNT) were remarkably low in all seropositive goats. Virus isolation from whole-blood was possible at the peak of viremia until 49 dpi. Moreover, detection of BTV-27v02-RNA and Ab in one contact goat indicated that-similar to BTV-26-at least one of three BTV-27 variants may be transmitted by contact between goats. In the field, BTV-27 RNA can be detected up to 6 months in the whole-blood of BTV-27-infected Corsican goats. In contrast, BTV RNA was not detected in the blood of cattle or sheep. In addition, BTV-27 Abs were not detected in cattle and only a transient increase in Ab levels was observed in some sheep. None of the 30 animals showed obvious BT-like clinical signs. In summary, the phenotypes observed for BTV-27v01-v03 phenotypes correspond to a mixture of characteristics known for BTV-25 and 26.

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.

Bluetongue: control, surveillance and safe movement of animals

The performance of different bluetongue control measures related to both vaccination and protection from bluetongue virus (BTV) vectors was assessed. By means of a mathematical model, it was concluded that when vaccination is applied on 95% of animals even for 3 years, bluetongue cannot be eradicated and is able to re‐emerge. Only after 5 years of vaccination, the infection may be close to the eradication levels. In the absence of vaccination, the disease can persist for several years, reaching an endemic condition with low level of prevalence of infection. Among the mechanisms for bluetongue persistence, the persistence in the wildlife, the transplacental transmission in the host, the duration of viraemia and the possible vertical transmission in vectors were assessed. The criteria of the current surveillance scheme in place in the EU for demonstration of the virus absence need revision, because it was highlighted that under the current surveillance policy bluetongue circulation might occur undetected. For the safe movement of animals, newborn ruminants from vaccinated mothers with neutralising antibodies can be considered protected against infection, although a protective titre threshold cannot be identified. The presence of colostral antibodies interferes with the vaccine immunisation in the newborn for more than 3 months after birth, whereas the minimum time after vaccination of animal to be considered immune can be up to 48 days. The knowledge about vectors ecology, mechanisms of over‐wintering and criteria for the seasonally vector‐free period was updated. Some Culicoides species are active throughout the year and an absolute vector‐free period may not exist at least in some areas in Europe. To date, there is no evidence that the use of insecticides and repellents reduce the transmission of BTV in the field, although this may reduce host/vector contact. By only using pour‐on insecticides, protection of animals is lower than the one provided by vector‐proof establishments.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1182/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1171/full

Design of virus-based nanomaterials for medicine, biotechnology, and energy

This review provides an overview of recent developments in "chemical virology." Viruses, as materials, provide unique nanoscale scaffolds that have relevance in chemical biology and nanotechnology, with diverse areas of applications. Some fundamental advantages of viruses, compared to synthetically programmed materials, include the highly precise spatial arrangement of their subunits into a diverse array of shapes and sizes and many available avenues for easy and reproducible modification. Here, we will first survey the broad distribution of viruses and various methods for producing virus-based nanoparticles, as well as engineering principles used to impart new functionalities. We will then examine the broad range of applications and implications of virus-based materials, focusing on the medical, biotechnology, and energy sectors. We anticipate that this field will continue to evolve and grow, with exciting new possibilities stemming from advancements in the rational design of virus-based nanomaterials.

Vaccines for Prevention of Bluetongue and Epizootic Hemorrhagic Disease in Livestock: A North American Perspective

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) are noncontagious, insect-transmitted diseases of domestic and wild ruminants caused by related but distinct viruses. There are significant gaps in our scientific knowledge and available countermeasures to control an outbreak of orbivirus-induced disease, whether BT or EHD. Both BT virus (BTV) and EHD virus (EHDV) cause hemorrhagic fevers in susceptible ruminants; however, BT is principally a disease of domestic livestock whereas EHD is principally a disease of certain species of wild, non-African ungulates, notably white-tailed deer. The live-attenuated (modified live virus [MLV]) vaccines available in the United States for use in small ruminant livestock do provide good protection against clinical disease following infection with the homologous virus serotype. Although there is increasing justification that the use of MLV vaccines should be avoided if possible, these are the only vaccines currently available in the United States. Specifically, MLVs are used in California to protect sheep against infection with BTV serotypes 10, 11, and 17, and a MLV to BTV serotype 10 is licensed for use in sheep throughout the United States. These MLV vaccines may need to continue to be used in the immediate future for protective immunization of sheep and goats against BT. There are currently no licensed vaccines available for EHD in the United States other than autogenous vaccines. If there is a need to rapidly develop a vaccine to meet an emerging crisis associated with either BTV or EHDV infections, development of an inactivated virus vaccine in a conventional adjuvanted formulation will likely be required. With two doses of vaccine (and in some instances just one dose), inactivated vaccines can provide substantial immunity to the epizootic serotype of either BTV or EHDV. This strategy is similar to that used in the 2006-2008 BTV serotype 8 outbreaks in northern Europe that provided vaccine to the field within 2 years of the initial incursion (by 2008). Further research and development are warranted to provide more efficacious and effective vaccines for control of BTV and EHDV infections.

The application of virus-like particles as vaccines and biological vehicles

Virus-like particles (VLPs) can be spontaneously self-assembled by viral structural proteins under appropriate conditions in vitro while excluding the genetic material and potential replication probability. In addition, VLPs possess several features including can be rapidly produced in large quantities through existing expression systems, highly resembling native viruses in terms of conformation and appearance, and displaying repeated cluster of epitopes. Their capsids can be modified via genetic insertion or chemical conjugation which facilitating the multivalent display of a homologous or heterogeneous epitope antigen. Therefore, VLPs are considered as a safe and effective candidate of prophylactic and therapeutic vaccines. VLPs, with a diameter of approximately 20 to 150 nm, also have the characteristics of nanometer materials, such as large surface area, surface-accessible amino acids with reactive moieties (e.g., lysine and glutamic acid residues), inerratic spatial structure, and good biocompatibility. Therefore, assembled VLPs have great potential as a delivery system for specifically carrying a variety of materials. This review summarized recent researches on VLP development as vaccines and biological vehicles, which demonstrated the advantages and potential of VLPs in disease control and prevention and diagnosis. Then, the prospect of VLP biology application in the future is discussed as well.

Peste des petits ruminants virus-like particles induce both complete virus-specific antibodies and virus neutralizing antibodies in mice

Peste des petits ruminants virus (PPRV), an etiological agent of peste des petits ruminants (PPR), is classified into the genus Morbillivirus in the family Paramyxoviridae. In a previous study, a recombinant baculovirus has been constructed to co-express the PPRV matrix (M), haemagglutinin (H) and nucleocapsid (N) proteins in insect cells, causing budding of PPR virus-like particles (VLPs) from insect cell membranes by viewing of ultrathin section with a transmission electron microscope. In this follow-up study, these PPR VLPs were purified by sucrose density gradient centrifugation for immunizing mice twice. Three weeks post-primary immunization and 2 weeks post-secondary immunization, all serum samples were obtained and subsequently subjected to indirect ELISA detection on complete virus-specific antibodies. In addition, all serum samples, which were collected 2 weeks post-secondary immunization, were used for virus neutralization test on PPRV neutralizing antibodies. The results showed that the purified PPR VLPs induced both types of antibodies mentioned above in mice, indicating a given potential of VLP-based vaccine candidate against PPR.

Plant-based vaccines against viruses

Plant-made or "biofarmed" viral vaccines are some of the earliest products of the technology of plant molecular farming, and remain some of the brightest prospects for the success of this field. Proofs of principle and of efficacy exist for many candidate viral veterinary vaccines; the use of plant-made viral antigens and of monoclonal antibodies for therapy of animal and even human viral disease is also well established. This review explores some of the more prominent recent advances in the biofarming of viral vaccines and therapies, including the recent use of ZMapp for Ebolavirus infection, and explores some possible future applications of the technology.

Subviral particle as vaccine and vaccine platform

Recombinant subvirual particles retain similar antigenic features of their authentic viral capsids and thus have been applied as nonreplicating subunit vaccines against viral infection and illness. Additionally, the self-assembled, polyvalent subviral particles are excellent platforms to display foreign antigens for immune enhancement for vaccine development. These subviral particle-based vaccines are noninfectious and thus safer than the conventional live attenuated and inactivated vaccines. While several VLP vaccines are available in the markets, numerous others, including dual vaccines against more than one pathogen, are under clinical or preclinical development. This article provides an update of these efforts.

Culicoides midge bites modulate the host response and impact on bluetongue virus infection in sheep

Many haematophagous insects produce factors that help their blood meal and coincidently favor pathogen transmission. However nothing is known about the ability of Culicoides midges to interfere with the infectivity of the viruses they transmit. Among these, Bluetongue Virus (BTV) induces a hemorrhagic fever- type disease and its recent emergence in Europe had a major economical impact. We observed that needle inoculation of BTV8 in the site of uninfected C. nubeculosus feeding reduced viraemia and clinical disease intensity compared to plain needle inoculation. The sheep that developed the highest local inflammatory reaction had the lowest viral load, suggesting that the inflammatory response to midge bites may participate in the individual sensitivity to BTV viraemia development. Conversely compared to needle inoculation, inoculation of BTV8 by infected C. nubeculosus bites promoted viraemia and clinical symptom expression, in association with delayed IFN- induced gene expression and retarded neutralizing antibody responses. The effects of uninfected and infected midge bites on BTV viraemia and on the host response indicate that BTV transmission by infected midges is the most reliable experimental method to study the physio-pathological events relevant to a natural infection and to pertinent vaccine evaluation in the target species. It also leads the way to identify the promoting viral infectivity factors of infected Culicoides in order to possibly develop new control strategies against BTV and other Culicoides transmitted viruses.

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.

Rapid generation of replication-deficient monovalent and multivalent vaccines for bluetongue virus: protection against virulent virus challenge in cattle and sheep

Since 1998, 9 of the 26 serotypes of bluetongue virus (BTV) have spread throughout Europe, and serotype 8 has suddenly emerged in northern Europe, causing considerable economic losses, direct (mortality and morbidity) but also indirect, due to restriction in animal movements. Therefore, many new types of vaccines, particularly subunit vaccines, with improved safety and efficacy for a broad range of BTV serotypes are currently being developed by different laboratories. Here we exploited a reverse genetics-based replication-deficient BTV serotype 1 (BTV-1) (disabled infectious single cycle [DISC]) strain to generate a series of DISC vaccine strains. Cattle and sheep were vaccinated with these viruses either singly or in cocktail form as a multivalent vaccine candidate. All vaccinated animals were seroconverted and developed neutralizing antibody responses to their respective serotypes. After challenge with the virulent strains at 21 days postvaccination, vaccinated animals showed neither any clinical reaction nor viremia. Further, there was no interference with protection with a multivalent preparation of six distinct DISC viruses. These data indicate that a very-rapid-response vaccine could be developed based on which serotypes are circulating in the population at the time of an outbreak.

Virus-like particles: promising platforms with characteristics of DIVA for veterinary vaccine design

In general, it is difficult to differentiate infected from vaccinated animals through vaccination with conventional vaccines, thereby impeding the serological surveillance of animal diseases. DIVA (differentiating infected from vaccinated animals) vaccine, originally known as marker vaccine, usually based on the absence of at least one immunogenic protein in the vaccine strain, allows DIVA in conjunction with a diagnostic test that detects antibodies against the antigens lacking in the vaccine strain. Virus-like particles (VLPs), composed of one or more structural proteins but no genomes of native viruses, mimic the organization and conformation of authentic virions but have no ability to self-replicate in cells, potentially yielding safer vaccine candidates. Since VLPs containing either monovalent or multivalent antigen can be produced in compliance with the requirements for serological surveillance, the use of VLP-based vaccines plays a promising role in DIVA vaccination strategies against animal diseases. Here, we critically reviewed VLPs and companion diagnostics with properties of DIVA for veterinary vaccine design, and three different VLPs as promising platforms for DIVA vaccination strategies in animals.