Efficacy of three inactivated vaccines against bluetongue virus serotype 8 in sheep

Serological Responses in Cattle following Booster Vaccination against Serotypes 4 and 8 Bluetongue Virus with Two Bivalent Commercial Inactivated Vaccines

Since the outbreak of bluetongue in Northern Europe in 2006, numerous outbreaks involving several serotypes have been observed. Since 2008, compulsory or voluntary vaccination campaigns with inactivated vaccines have been carried out to eradicate these serotypes. In France, serotypes 8 and 4 have been enzootic since 2017, and currently, the majority of vaccinations take place in the context of animal movements, to comply with the regulations of the importing countries. Several vaccine manufacturers have developed inactivated vaccines against serotypes 4 and 8 (mono or bivalent). In this study, we investigated and compared the serological responses to a booster vaccination with two different bivalent inactivated vaccines (BTVPUR suspension injectable^® 4 + 8, Boehringer Ingelheim or SYVAZUL ^® BTV 4 + 8, Biové) following a primary vaccination with BTVPUR^® 4 + 8 in the previous year. The results show that using an alternative vaccine for booster vaccination is at least as effective as using the homologous vaccine. Indeed, the antibody response against BTV-8 is higher in the case of a heterologous vaccination and identical for BTV-4. This information could allow more flexibility in the choice of vaccines used for booster vaccination, particularly in cases where homologous vaccines are in short supply or unavailable.

Safety and efficacy of a Bluetongue inactivated vaccine (serotypes 1 and 4) in sheep

A new inactivated vaccine against Bluetongue virus (BTV) serotypes 1 and 4, was developed from field isolates. Safety and efficacy of the vaccine were evaluated in sheep by serological monitoring and virus nucleic acid detection after experimental infection of vaccinated animals. Seroconversion was observed in vaccinated animals at day 14 post vaccination (pv) with neutralizing antibody titer of 1.9 and 1.8 for serotypes 1 and 4, respectively. The titer increase significantly after the booster reaching 2.7 and persist one year >1.5 for both serotypes. After challenge with virulent isolates, vireamia was recorded in control animals, as evident by q-PCR with threshold cycles (Ct) ranging from 24 to 31 and peaked at day 10 post challenge, while no vireamia was detected in vaccinated animals. Vaccinated sheep were fully protected against the disease and infection.

Codon Usage Bias Analysis of Bluetongue Virus Causing Livestock Infection

Bluetongue virus (BTV) is a double-stranded RNA virus with multiple segments and belongs to the genus Orbivirus within the family Reoviridae. BTV is spread to livestock through its dominant vector, biting midges of genus Culicoides. Although great progress has been made in genomic analyses, it is not fully understood how BTVs adapt to their hosts and evade the host's immune systems. In this study, we retrieved BTV genome sequences from the National Center for Biotechnology Information (NCBI) database and performed a comprehensive research to explore the codon usage patterns in 50 BTV strains. We used bioinformatic approaches to calculate the relative synonymous codon usage (RSCU), codon adaptation index (CAI), effective number of codons (ENC), and other indices. The results indicated that most of the overpreferred codons had A-endings, which revealed that mutational pressure was the major force shaping codon usage patterns in BTV. However, the influence of natural selection and geographical factors cannot be ignored on viral codon usage bias. Based on the RSCU values, we performed a comparative analysis between BTVs and their hosts, suggesting that BTVs were inclined to evolve their codon usage patterns that were comparable to those of their hosts. Such findings will be conducive to understanding the elements that contribute to viral evolution and adaptation to hosts.

Economic Impact of a Bluetongue Serotype 8 Epidemic in Germany

Background and Objectives: Germany was affected by Bluetongue virus serotype 8 (BTV-8) from 2006 to 2009 and recorded new cases since December 2018. We assessed the economic impact of the epidemic from the first cases in 2006 until 2018. Direct costs include production losses, animal deaths, and veterinary treatment. Indirect costs include surveillance, additional measures for animal export, disease control (preventive vaccination and treatment with insecticides), vector monitoring, and administration. Methodology: To estimate the financial impact of BTV-8 on different species and production types at the animal level, we performed a gross margin analysis (GMA) for dairy and beef cattle, and sheep. To estimate the impact on the national level, we used a modified framework described by Rushton et al. (1) and applied a methodology described by Bennett (2). Both the GMA and the economic model on national level were implemented in Excel and the Excel Add-in @Risk. The tools, which are widely applicable, also for other diseases, are made available here. Results: The financial impact of a BTV-8 infection at the animal level was estimated at 119-136 Euros in dairy cattle, at 27 Euros in beef cattle, and at 74 Euros in sheep. At the national level, the impact of the BTV-8 epidemic ranged between 157 and 203 million Euros (mean 180 million Euros). This figure consisted of 132 (73%) and 48 (27%) million Euros for indirect and direct costs. Indirect costs included 89 million Euros (67%) for vaccination, 18 million Euros (14%) for insecticide treatment, 15 million Euros (11%) for diagnostic testing of animals dispatched for trade, 8 million Euros (6%) for monitoring and surveillance, and 3 million Euros (2%) for administration. The highest costs were induced by a compulsory vaccination campaign in 2008 (51 million Euros; 28% of the total costs) and the disease impact on cattle in 2007 (30 million Euros; 17%). Discussion: We compare the outcome of our study with economic analyses of Bluetongue disease in other countries, and discuss the suitability of GMA and the developed tools for a wider application in veterinary economics.

Comparative Evaluation of T-Cell Immune Response to BTV Infection in Sheep Vaccinated with Pentavalent BTV Vaccine When Compared to Un-Vaccinated Animals

Recent invasion of multiple bluetongue virus serotypes (BTV) in different regions of the world necessitates urgent development of efficient vaccine that is directed against multiple BTV serotypes. In this experimental study, cell mediated immune response and protective efficacy of binary ethylenimine (BEI) inactivated Montanide^™ ISA 206 adjuvanted pentavalent (BTV-1, 2, 10, 16 and 23) vaccine was evaluated in sheep and direct challenge with homologous BTV serotypes in their respective group. Significant (P < 0.05) up-regulation of mRNA transcripts of IFN-α, IL-2, IL-6, IL-12, IFN-γ and TNF-α in PBMCs of vaccinated animals as compared to control (un-vaccinated) animals at certain time points was observed. On the other hand, there was a significant increase in mean ± SD percentage of CD8⁺ T cells after 7 days post challenge (DPC) but, the mean ± SD percentage of CD4⁺ T-cell population slightly declined at 7 DPC and enhanced after 14 DPC. Significant differences (P < 0.05) of CD8⁺ and CD4⁺T cells population was also observed between vaccinated and unvaccinated sheep. The vaccine also significantly (P < 0.05) reduced BTV RNA load in PBMCs of vaccinated animals than unvaccinated animals following challenge. There were no significant difference (P > 0.05) in cytokine induction, BTV RNA load and CD8⁺ and CD4⁺cell count among BTV-1, 2, 10, 16 and 23 serotype challenges except significant increase in mean ± SD percentage of CD8⁺ in BTV-2 group. These findings put forwarded that binary ethylenimine inactivated montanide adjuvanted pentavalent bluetongue vaccine has stimulated cell mediated immune response and most importantly reduced the severity of BTV-1, 2, 10, 16 and 23 infections following challenge in respective group.

A comparison of different vaccination schemes used in sheep combining inactivated bluetongue vaccines against serotypes 4 and 8

Eight different vaccination schemes using four commercially available inactivated Bluetongue vaccines against serotypes 4 and 8 in three different combinations (setting 1-3) were tested under field conditions for their ability to generate a measurable immune response in sheep. Animals of setting 1 (groups A-D) were simultaneously vaccinated using either individual injections at different locations (groups A & D) or double injection by a twin-syringe (groups B & C). For both application methods, a one-shot vaccination (groups C & D) was compared to a boosted vaccination (groups A & B). Sheep of setting 2 (groups E-G) were vaccinated in an alternating, boosted pattern at fortnightly intervals starting with serotype 4 (groups E & F) or vice versa (group G). Group H of setting 3 was vaccinated simultaneously and vaccines were injected individually as a one-shot application. Each group consisted of 30 sheep. The immunogenic response was tested in all sheep (n = 240) by ELISA (IDScreen®Bluetongue Competition), while serum neutralisation tests were performed in five to six sheep from each group (n = 45). All vaccine combinations were well tolerated by all sheep. Of all vaccines and schemes described, the simultaneous double injected boosted vaccination of setting 1 (group B) yielded the highest median serotype-specific titres 26 weeks after the first vaccination (afv) and 100% seropositive animals (ELISA) one year afv. In setting 1, there were no relevant significant differences in the immunogenic response between simultaneously applied vaccines at different sites or at the same injection site. Importantly, a one-shot vaccination induced comparable immunogenicity to a boosted injection half a year afv. Low serotype-specific neutralising antibody levels were detected in settings 2 and 3 and are attributed to diverse factors which may have influenced the measured immunogenicity.

Presence of Antibodies against Bluetongue Virus (BTV) in Sheep 5 to 7.5 Years after Vaccination with Inactivated BTV-8 Vaccines

Thirty-six female sheep, previously vaccinated against Bluetongue virus serotype 8 (BTV-8) using inactivated vaccines, were included in this field study. In Germany, vaccination was compulsory in 2008 and 2009, voluntary in 2010 and early 2011, and later, was prohibited in 2011. Due to their age, eighteen sheep had been vaccinated for two or more consecutive years, while a further eighteen animals had only been vaccinated once or not at all. The sheep were blood sampled five (n = 31) to 7.5 years (n = 5) after their last vaccination. All serum samples (n = 36) were tested for BTV group-specific antibodies by an ELISA (IDScreen^® Bluetongue Competition assay, ID Vet). In five of the animals, the BTV-8 serotype-specific antibody titers were measured by serum neutralization (SN). The majority of sheep that were vaccinated annually for two or more years showed a positive ELISA (14/18 sheep) and a SN (two of two sheep) result 5 years after their last vaccination. Most of the sheep vaccinated fewer than twice showed a negative ELISA result 5 to 7.5 years after their last vaccination (13/18 animals). The three animals in this group tested by SN showed one negative and two positive results. This short communication is the first to describe the presence of BTV antibodies in sheep 5 to 7.5 years after vaccination with inactivated BTV-8 vaccines.

BTV antibody longevity in cattle five to eight years post BTV-8 vaccination

The Bluetongue virus serotype -8 (BTV-8) epizootic in Germany (2006-2008) was successfully eradicated, essentially by the massive application of commercially available inactivated BTV-8 vaccines. While a six-year antibody longevity of BTV antibodies post BTV-8 vaccination in cattle has been described previously, our study investigated the BTV-8-vaccine antibodies in cattle for up to eight years. In total, 157 bovine serum samples were analysed for the presence of group-specific BTV antibodies in both a commercial cELISA, and a BTV-8- specific serum neutralization test. A robust number of cattle were seropositive for group- and serotype-specific neutralising antibodies for five or more years. In selected animals, born and vaccinated in 2009 or later, the presence of BTV antibodies for up to eight years post BTV-8 vaccination could be confirmed. Our data also show, that booster vaccination prolonged the antibody longevity of vaccine-induced antibodies and the number of serologically positive cattle.

Beta-propiolactone inactivated bivalent bluetongue virus vaccine containing Montanide ISA-71VG adjuvant induces long-term immune response in sheep against serotypes 4 and 16 even after 3 years of controlled vaccine storage

In this study, we developed and evaluated the beta-propiolactone inactivated bivalent bluetongue virus (BTV) serotypes 4 and 16 vaccine delivered with Montanide™ ISA-71VG adjuvant. The safety, stability and immunological profile of the fresh and after three years of long-term storage of the vaccine formulation was analyzed. We observed after long-term storage that the vaccine emulsion was stable as indicated by unchanged pH and viscosity. The stored vaccine formulation induced virus neutralizing antibodies (VNA) in sheep against both the bluetongue virus serotypes at 7-10 day post-vaccination (dpv). VNA titers reached the peak by 60 dpv and detectable during the entire study period. Antibodies against bluetongue virus structural protein VP7 were detected by ELISA in all BTV vaccinated experimental animal groups. Partial clinical protection was observed in vaccinates against challenge virulent BTV-4 and BTV-16 serotypes by 10 dpv, while complete protection was observed at 14 dpv. The levels of viremia was decreased in challenged sheep by 10 dpv while the viremia was undetectable by 14 dpv. In summary, our newly formulated bivalent BTV (BTV-4 and BTV-16) vaccine delivered with Montanide™ ISA-71VG adjuvant was found safe and stable for over three years and induced protective response in sheep.

A comprehensive study on seroprevalence of bluetongue virus in Haryana state of India

AIM

The aim of present study was to determine seroprevalence of bluetongue virus (BTV) in Haryana state of India.

MATERIALS AND METHODS

A total of 803 serum samples, 408 of cattle and 395 of buffalo origin, respectively, were collected from different villages of Haryana. Sampling was done randomly to obtain unbiased results. The samples were evaluated by a competitive enzyme-linked immunosorbent assay for the presence of BTV antibodies.

RESULTS

Overall seroprevalence of BTV antibody in cattle and buffaloes for all 21 districts of Haryana state was found to be 75.49% and 92.91%, respectively. The prevalence of BTV in different agroclimatic zones ranged between 72-77% and 90-94% for cattle and buffalo, respectively. In buffaloes, the BTV seroprevalence was comparatively higher than in cattle.

CONCLUSION

The study showed that BTV is circulating in cattle and buffalo populations in the Northern part of India.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bluetongue

A specific concept of strain was developed in order to classify the BTV serotypes ever reported in Europe based on their properties of animal health impact: the genotype, morbidity, mortality, speed of spread, period and geographical area of occurrence were considered as classification parameters. According to this methodology the strain groups identified were (i) the BTV strains belonging to serotypes BTV‐1–24, (ii) some strains of serotypes BTV‐16 and (iii) small ruminant‐adapted strains belonging to serotypes BTV‐25, ‐27, ‐30. Those strain groups were assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7, Article 5 on the eligibility of bluetongue to be listed, Article 9 for the categorisation according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to bluetongue. The assessment has been performed following a methodology composed of information collection, expert judgement at individual and collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. The strain group BTV (1–24) can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL, while the strain group BTV‐25–30 and BTV‐16 cannot. The strain group BTV‐1–24 meets the criteria as in Sections 2 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (b) and (e) of Article 9(1) of the AHL. The animal species that can be considered to be listed for BTV‐1–24 according to Article 8(3) are several species of Bovidae, Cervidae and Camelidae as susceptible species; domestic cattle, sheep and red deer as reservoir hosts, midges insect of genus Culicoides spp. as vector species.

The development of a real-time reverse transcription-polymerase chain reaction (rRT-PCR) assay using TaqMan technology for the pan detection of bluetongue virus (BTV)

Bluetongue virus (BTV) is an infectious, non-contagious viral disease of domestic and wild ruminants that is transmitted by adult females of certain Culicoides species. Since 2006, several serotypes including BTV-1, 2, 4, 6, 8, 9 and 16, have spread from the Mediterranean basin into Northern Europe for the first time. BTV-8 in particular, caused a major epidemic in northern Europe. As a result, it is evident that most European countries are at risk of BTV infection. The objective of this study was to develop and validate a real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) assay based on TaqMan technology for the detection of representative strains of all BTV serotypes. Primers and probes were based on genome segment 10 of the virus, the NS3 gene. The assay was tested for sensitivity, and specificity. The analytical sensitivity of the rRT-PCR assay was 200 copies of RNA per reaction. The assay did not amplify the closely related orbivirus epizootic hemorrhagic disease virus (EHDV) but successfully detected all BTV reference strains including clinical samples from animals experimentally infected with BTV-8. This real time RT-PCR assay offers a sensitive, specific and rapid alternative assay for the pan detection of BTV that could be used as part of a panel of diagnostic assays for the detection of all serotypes of BTV.

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

Immunosuppression in sheep induced by cyclophosphamide, bluetongue virus and their combination: Effect on clinical reaction and viremia

The main purpose of this work was to establish an experimental model for immunosuppression in sheep, and evaluate its possible effects on bluetongue viremia. Animals were allocated in 4 groups: Cy (cyclophosphamide), BT (bluetongue), CyBT (combined Cy and BT) and Co (control), and underwent clinical evaluations, virological testing, peripheral blood immunophenotyping and determination of antiviral humoral immune responses. Intravenous administration of cyclophosphamide (37.5 mg/kg body weight) resulted in immunosuppresion induction, as significant drops were observed in blood leukocytes and lymphocyte subset counts (CD2⁺, CD4⁺, CD8⁺, CD19⁺), lasting 3-10 days after its administration. Reduction in B-cell (CD19⁺) counts was more pronounced than in T-/NK-cell (CD2⁺) counts (92% and 59%, respectively). BTV-9 inoculation resulted in pronounced lymphocytopenia observed from day 1 post-inoculation. Their combined administration resulted in a more intense immunosuppressive effect, as indicated by the greater reduction in lymphocyte, granulocyte, CD4⁺ and CD8⁺ cell counts. In group CyBT, earlier initiation of fever by one day (day 6 p.i.) compared to group BT (day 7 p.i.), and delay in antibody responses by one day was observed, compared to group BT. Neutralizing antibodies in both groups (BT, CyBT) were detectable from day 10 p.i., but no significant titer differences were observed. Infectious virus titers were detected from day 4 p.i. in group BT and from day 3 in group CyBT. Statistical significances in virus titers were also observed (greatest mean titer difference: 1.4 log₁₀ CEID₅₀/ml RBCs at day 5 p.i., P < 0.001), indicating possible impact of immunosuppression on virus transmission and epidemiology of bluetongue.

Current and next-generation bluetongue vaccines: Requirements, strategies, and prospects for different field situations

Bluetongue virus (BTV) causes the hemorrhagic disease bluetongue (BT) in ruminants. The best way to control outbreaks is vaccination. Currently, conventionally modified-live and inactivated vaccines are commercially available, which have been successfully used to control BT, but nonetheless have their specific shortcomings. Therefore, there is a need for improved BT vaccines. The ideal BT vaccine is efficacious, safe, affordable, protective against multiple serotypes and enables the differentiation of infected from vaccinated animals. Different field situations require specific vaccine profiles. Single serotype outbreaks in former BT-free areas need rapid onset of protection against viremia of the respective serotype. In contrary, endemic multiple serotype situations require long-lasting protection against all circulating serotypes. The ideal BT vaccine for all field situations does not exist and balancing between vaccine properties is needed. Many new vaccines candidates, ranging from non-replicating subunits to replicating next-generation reverse genetics based vaccines, have been developed. Some have been tested extensively in large numbers of ruminants, whereas others were developed recently and have only been tested in vitro and in mice models. Most vaccine candidates are promising, but have their specific shortcomings and advantages. In this review, current and next-generation BT vaccines are discussed in the light of prerequisites for different field situations.

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.

Bluetongue in small ruminants: An opinionated review, with a brief appraisal of the 2014 outbreak of the disease in Greece and the south-east Europe

Bluetongue is an arthropod-borne viral disease of ruminants, especially of sheep, caused by Bluetongue virus, which belongs to the genus Orbivirus of the family Reoviridae and is classified into 26 antigenically distinct serotypes. Once thought to be restricted in Africa and parts of the Middle East, bluetongue has now become a concern in sheep-rearing countries around the world. In the past 10 years, severe outbreaks have occurred in Europe with important economic consequences; of these, the 2006-20008 outbreak in Europe was caused by a serotype 8 strain and the 2014 outbreak in Greece and the other countries of south-east Europe was caused by a serotype 4 strain, suggested to be a reassortant strain with genome segments from lineages of serotype 1, 2 and 4. Immunisation campaigns can be implemented for successful control and limiting of the disease. Nevertheless, in both of the above outbreaks, late application of vaccinations led to a wide spread of the disease, which subsequently resulted in significant losses in livestock in the affected regions. In view of that, standardisation of control measures in the future will be beneficial for efficiently limiting outbreaks of the disease.

Evaluation of adaptive immune responses and heterologous protection induced by inactivated bluetongue virus vaccines

Eradication of bluetongue virus is possible, as has been shown in several European countries. New serotypes have emerged, however, for which there are no specific commercial vaccines. This study addressed whether heterologous vaccines would help protect against 2 serotypes. Thirty-seven sheep were randomly allocated to 7 groups of 5 or 6 animals. Four groups were vaccinated with commercial vaccines against BTV strains 2, 4, and 9. A fifth positive control group was given a vaccine against BTV-8. The other 2 groups were unvaccinated controls. Sheep were then challenged by subcutaneous injection of either BTV-16 (2 groups) or BTV-8 (5 groups). Taken together, 24/25 sheep from the 4 experimental groups developed detectable antibodies against the vaccinated viruses. Furthermore, sheep that received heterologous vaccines showed significantly reduced viraemia and clinical scores for BTV-16 when compared to unvaccinated controls. Reductions in clinical signs and viraemia among heterologously vaccinated sheep were not as common after challenge with BTV-8. This study shows that heterologous protection can occur, but that it is difficult to predict if partial or complete protection will be achieved following inactivated-BTV vaccination.

Why German farmers have their animals vaccinated against Bluetongue virus serotype 8: results of a questionnaire survey

In response to the Bluetongue disease epidemic in 2006-2007, Germany started in 2008 a country-wide mandatory vaccination campaign. By 2009 the number of new outbreaks had decreased so that vaccination became voluntary in 2010. We conducted a questionnaire survey in cattle and sheep farms in three German federal states, namely North-Rhine Westphalia, Rhineland Palatinate and Saxony-Anhalt to estimate the vaccination uptake in 2010, the intention to vaccinate in 2011 and the main determinants of refusal or acceptance to do so. The results showed that 42.8% (40.6-45.1) of the cattle farmers and 33.8% (31.8-35.8) of the sheep farmers had their animals vaccinated in 2010, whereas 40.7% (38.5-43.0) of cattle and 37.93% (35.8-40.1) sheep farmers expressed their intention to vaccinate in 2011. The main reasons mentioned for having animals vaccinated against BTV-8 were ability to export animals, prevention of production losses, subsidized vaccination, and recommendation by the veterinarian. Motives for refusing vaccination were presumed low risk of infection, costs, absence of clinical BT symptoms, presumed negative cost-benefit ratio, and negative experience with previous vaccination events (side effects). We assume that in order to increase farmers' motivation to have their animals immunized against BTV-8, (1) the vaccination needs to be subsidized, (2) combined vaccines with several different BT serotypes or even other diseases should be available and (3) farmers need to be better informed about the safety and benefit of vaccination.

Wild ungulates as sentinel of BTV-8 infection in piedmont areas

Bluetongue caused by the genotype 8 virus (BTV-8) appeared for the first time in BTV free areas in northern Italy in 2008. The presence of domestic animals outbreaks, abundant wild ungulates populations, and ongoing regional BTV control plans, made this area interesting to evaluate the role of wild ruminants in BTV-8 epidemiology. We analyzed spleen samples from hunted red deer (Cervus elaphus), roe deer (Capreolus capreolus) and Alpine chamois (Rupicapra rupicapra) by quantitative RT-PCR. Samples were collected from 2008 to 2011 in two provinces of Piedmont region. BTV-8 was detected in all ungulate species, confirming their receptivity to the infection. However, the viral load in the positive specimens was low, and decreased from 2008 to 2011. These results, together with the extinction of the epidemic following a regional livestock vaccination campaign, lead to hypothesize that wild ungulates were an epiphenomenon and they had not an important role in the domestic transmission cycle of BTV-8 in this area. In spite of this, wild ruminants appear to be good sentinels of BTV circulation and their monitoring could be useful for surveillance in piedmont areas.

Long-term dynamics of bluetongue virus in wild ruminants: relationship with outbreaks in livestock in Spain, 2006-2011

Wild and domestic ruminants are susceptible to Bluetongue virus (BTV) infection. Three BTV serotypes (BTV-4, BTV-1 and BTV-8) have been detected in Spain in the last decade. Even though control strategies have been applied to livestock, BTV circulation has been frequently detected in wild ruminant populations in Spain. The aim of the present study is to assess the role for wild ruminants in maintaining BTV after the vaccination programs in livestock in mainland Spain. A total of 931 out 1,914 (48.6%) serum samples, collected from eight different wild ruminant species between 2006 and 2011, were BTV positive by ELISA. In order to detect specific antibodies against BTV-1, BTV-4 and BTV-8, positive sera were also tested by serumneutralisation test (SNT). From the ELISA positive samples that could be tested by SNT (687 out of 931), 292 (42.5%) showed neutralising antibodies against one or two BTV serotypes. For each BTV seroptype, the number of outbreaks in livestock (11,857 outbreaks in total) was modelled with pure autoregressive models and the resulting smoothed values, representing the predicted number of BTV outbreaks in livestock at municipality level, were positively correlated with BTV persistence in wild species. The strength of this relationship significantly decreased as red deer (Cervus elaphus) population abundance increased. In addition, BTV RNA was detected by real time RT-PCR in 32 out of 311 (10.3%) spleen samples from seropositive animals. Although BT outbreaks in livestock have decreased substantially after vaccination campaigns, our results indicated that wild ruminants have been exposed to BTV in territories where outbreaks in domestic animals occurred. The detection of BTV RNA and spatial association between BT outbreaks in livestock and BTV rates in red deer are consistent with the hypothesis of virus circulation and BTV maintenance within Iberian wild ruminant populations.

Did vaccination slow the spread of bluetongue in France?

Vaccination is one of the most efficient ways to control the spread of infectious diseases. Simulations are now widely used to assess how vaccination can limit disease spread as well as mitigate morbidity or mortality in susceptible populations. However, field studies investigating how much vaccines decrease the velocity of epizootic wave-fronts during outbreaks are rare. This study aimed at investigating the effect of vaccination on the propagation of bluetongue, a vector-borne disease of ruminants. We used data from the 2008 bluetongue virus serotype 1 (BTV-1) epizootic of southwest France. As the virus was newly introduced in this area, natural immunity of livestock was absent. This allowed determination of the role of vaccination in changing the velocity of bluetongue spread while accounting for environmental factors that possibly influenced it. The average estimated velocity across the country despite restriction on animal movements was 5.4 km/day, which is very similar to the velocity of spread of the bluetongue virus serotype 8 epizootic in France also estimated in a context of restrictions on animal movements. Vaccination significantly reduced the propagation velocity of BTV-1. In comparison to municipalities with no vaccine coverage, the velocity of BTV-1 spread decreased by 1.7 km/day in municipalities with immunized animals. For the first time, the effect of vaccination has been quantified using data from a real epizootic whilst accounting for environmental factors known to modify the velocity of bluetongue spread. Our findings emphasize the importance of vaccination in limiting disease spread across natural landscape. Finally, environmental factors, specifically those related to vector abundance and activity, were found to be good predictors of the velocity of BTV-1 spread, indicating that these variables need to be adequately accounted for when evaluating the role of vaccination on bluetongue spread.

Eradication of bluetongue disease in Germany by vaccination

Bluetongue disease first broke out in Germany on 21 August 2006, almost simultaneously with the first outbreaks in Belgium and The Netherlands. More extensive tests showed that the serotype was serotype 8. Due to westerly winds the disease spread rapidly towards the East, with the result that in the year 2008 large parts of Germany were affected. The traditional methods of animal disease control were not of much help in view of the transmission of the disease by insects; the speed of the spread of the disease could only be slowed down by movement restrictions, but could not be influenced in a decisive manner. Authorised vaccines were not (yet) available. A large-scale field study based on three prototypes in bovine animals and sheep revealed that they were both effective and safe. Consequently, the Federal Ministry of Food, Agriculture and Consumer Protection issued an exceptional permission to administer these non-authorised vaccines. In May 2008, large-scale vaccination campaigns were launched (vaccination of all bovines, sheep and goats). As a consequence, the disease outbreak figures declined drastically. In 2009, the last blanket vaccinations were administered and from 2010 animal keepers were allowed to continue vaccinating their livestock on a voluntary basis. Intensive tests (serological, PCR) showed in the years 2010 and 2011 that BTV8 no longer circulated among the livestock population. Effective from 15.02.2012, Germany declared itself free from BTV8 in line with Article 8.3.3 of the OIE Animal Health Code.

Pulmonary artery haemorrhage in newborn calves following bluetongue virus serotype 8 experimental infections of pregnant heifers

The emergence of bluetongue disease (BT) among livestock in Europe in 2006 raised many questions including the occurrence and epidemiological significance of foetal infections in cattle. To clarify these aspects, vaccinated and unvaccinated pregnant heifers were sequentially infected twice in an isolation facility (biosafety level 3) with a northern European outbreak strain of Bluetongue virus serotype 8 (BTV-8). The study was terminated 2 months after calving with necropsy of the dams and their offspring. The cattle were monitored throughout the study by clinical scoring and for the presence of circulating neutralising antibodies, and after calving for the presence of infectious virus and viral RNA in blood and milk. Four calves, one born from a vaccinated dam and three from non-vaccinated ones, that were infected at 120 days of gestation had obvious haemorrhage of the pulmonary artery at necropsy. Although haemorrhage of the pulmonary artery is highly characteristic of BT, viral RNA was not detected in any of these calves. Furthermore, although none of the calves born from heifers infected prior to mid-gestation had teratogenic BTV typical brain lesions, some had lesions at birth suggestive of in utero BTV infection. Despite the lack of viral RNA detection, the presence of haemorrhage of the pulmonary artery deserves to be reported as a new observation in the context of the multiple investigations having as main subject the BTV placental crossing in cattle.

Schmallenberg virus experimental infection of sheep

Since late 2011, a novel orthobunyavirus, named Schmallenberg virus (SBV), has been implicated in many cases of severely malformed bovine and ovine offspring in Europe. In adult cattle, SBV is known to cause a mild transient disease; clinical signs include short febrile episodes, decreased milk production and diarrhoea for a few days. However, the knowledge about clinical signs and pathogenesis in adult sheep is limited. In the present study, adult sheep of European domestic breeds were inoculated with SBV either as cell culture grown virus or as virus with no history of passage in cell cultures. Various experimental set-ups were used. Sampling included blood collection at different time points during the experimental period and selected organ material at autopsy. Data from this study showed, that the RNAemic period in sheep was as short as reported for cattle; viral genome was detectable for about 3-5 days by real-time RT-PCR. In total, 13 out of 30 inoculated sheep became RNAemic, with the highest viral load in animals inoculated with virus from low cell culture passaged or the animal passaged material. Contact animals remained negative throughout the study. One RNAemic sheep showed diarrhoea for several days, but fever was not recorded in any of the animals. Antibodies were first detectable 10-14 days post inoculation. Viral RNA was detectable in spleen and lymph nodes up to day 44 post inoculation. In conclusion, as described for cattle, SBV-infection in adult sheep predominantly results in subclinical infection, transient RNAemia and a specific antibody response. Maintenance of viral RNA in the lymphoreticular system is observed for an extended period.

Evaluation of the humoral immune responses in adult cattle and sheep, 4 and 2.5 years post-vaccination with a bluetongue serotype 8 inactivated vaccine

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ELISA antibodies persist in serum and milk for at least 4 years post-vaccination in cattle.

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ELISA-based milk/serum surveillance is not possible for at least 4 years post-vaccination in cattle, but surveillance is possible in young unvaccinated cattle.

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Neutralising antibodies persist for at least 4 years post-vaccination (two vaccine doses four weeks apart) in cattle.

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Neutralising antibodies persist for at least 2.5 years post-vaccination (two vaccine doses one year apart) in sheep.

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Protection is likely for at least 4 and 2.5 years post-vaccination in cattle and in sheep respectively.

One of the big surprises about the devastating outbreak of bluetongue serotype-8 that spread across Northern and Western Europe between 2006 and 2008 was how relatively quickly the virus was controlled and eradicated from affected countries. This was at least in part attributed to the high levels of vaccine coverage achieved in affected countries. A previous study revealed that neutralising antibodies persisted in the majority of vaccinated cattle for at least 3 years post-vaccination, indicating that cattle are likely to be protected for this time period. The current study revealed that neutralising antibodies persisted in the same group of cattle for up to 4 years post-vaccination, and that neutralising antibodies persisted for up to 2.5 years in sheep that had been vaccinated on two occasions one year apart. These results have implications for future bluetongue surveillance programmes and vaccine control strategies.

Evaluation of the immunogenicity of an experimental subunit vaccine that allows differentiation between infected and vaccinated animals against bluetongue virus serotype 8 in cattle

Bluetongue virus (BTV), the causative agent of bluetongue in ruminants, is an emerging virus in northern Europe. The 2006 outbreak of BTV serotype 8 (BTV-8) in Europe was marked by an unusual teratogenic effect and a high frequency of clinical signs in cattle. Conventional control strategies targeting small ruminants were therefore extended to include cattle. Since cattle were not routinely vaccinated before 2006, the immune responses to BTV have not been studied extensively in this species. With the aims of developing a subunit vaccine against BTV-8 for differentiation between infected and vaccinated animals based on viral protein 7 (VP7) antibody detection and of improving the current understanding of the immunogenicity of BTV proteins in cattle, the immune responses induced by recombinant VP2 (BTV-8) and nonstructural protein 1 (NS1) and NS2 (BTV-2) were studied. Cows were immunized twice (with a 3-week interval) with the experimental vaccine, a commercial inactivated vaccine, or a placebo. The two vaccines induced similar neutralizing antibody responses to BTV-8. Furthermore, the antibody responses detected against VP2, NS1, and NS2 were strongest in the animals immunized with the experimental vaccine, and for the first time, a serotype cross-reactive antibody response to NS2 was shown in cattle vaccinated with the commercial vaccine. The two vaccines evoked measurable T cell responses against NS1, thereby supporting a bovine cross-reactive T cell response. Finally, VP7 seroconversion was observed after vaccination with the commercial vaccine, as in natural infections, but not after vaccination with the experimental vaccine, indicating that the experimental vaccine may allow the differentiation of vaccinated animals from infected animals regardless of BTV serotype. The experimental vaccine will be further evaluated during a virulent challenge in a high-containment facility.

A one-year follow-up of antibody response in cattle and sheep after vaccination with serotype 8- and serotype 1-inactivated BT vaccines

Sixteen sheep and 18 cattle were followed up during 1 year to estimate the duration of immunity induced by inactivated bluetongue virus serotype 8 (BTV-8) vaccines (sheep and cattle) and a bluetongue virus serotype 1 (BTV-1) vaccine (cattle) under field conditions using cELISA and seroneutralization test (SNT). Four sheep never seroconverted. Those that seroconverted were all seronegative by BTV-8 SNT at the date of last sampling [378 days post-vaccination (dpv)]. Eight sheep were still positive by competitive ELISA (cELISA) 378 dpv. All the cattle seroconverted. At the end of the study, eight and 11 cattle were still positive by BTV-8 SNT and cELISA, respectively (335 dpv); and nine were still positive by BTV-1 SNT (301 dpv).

‘Schmallenberg virus’ – a novel orthobunyavirus emerging in Europe

In 2011, a novel orthobunyavirus of the Simbu serogroup, the Schmallenberg virus (SBV), was discovered using a metagenomic approach. SBV caused a large epidemic in Europe in ruminants. As with related viruses such as Akabane virus, it appears to be transmitted by biting midges. Transplacental infection often results in the birth of malformed calves, lambs and goat kids. In more than 5000 farms in Germany, The Netherlands, Belgium, France, UK, Italy, Spain, Luxembourg, Denmark and Switzerland acute infections of adult ruminants or malformed SBV-positive offspring were detected, and high seroprevalences were seen in adult ruminants in the core regions in The Netherlands, Germany and Belgium. The discovery of SBV, the spread of the epidemic, the role of vectors, the impact on livestock, public health issues, SBV diagnosis and measures taken are described in this review. Lessons to be learned from the Schmallenberg virus epidemic and the consequences for future outbreaks are discussed.

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

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

Detection of neutralizing antibodies against Bluetongue virus serotype 8 by an optimized plasma neutralization test

The neutralization test is used commonly for quantifying neutralizing antibodies and for distinguishing among different virus serotypes (serotyping). Due to the co-circulation of multiple serotypes of Bluetongue virus (BTV), the neutralization test has become an important surveillance method in Europe. However, the existence of different protocols makes test standardization and interpretation of results difficult. The current paper describes the development of a neutralization test using plasma and addresses the factors critical for detection of neutralizing antibodies against BTV serotype 8 (BTV-8), such as virus propagation, stability of virus infectivity and origin of the BTV-8 strain. The results indicated that animals exposed to the Northern European BTV-8 strain developed low neutralizing antibody titers, particularly after vaccination and experimental infection. Although clearly ELISA-positive, these samples often yielded false negative results when tested by the neutralization test using the OIE recommended virus concentration of 100 TCID₅₀/50 μl. The sensitivity of the neutralization test could be improved significantly with retained specificity by using a reduced TCID₅₀ and the homologous European BTV-8 strain instead of the South African reference strain.

Protection of Spanish Ibex (Capra pyrenaica) against Bluetongue virus serotypes 1 and 8 in a subclinical experimental infection

Many wild ruminants such as Spanish ibex (Capra pyrenaica) are susceptible to Bluetongue virus (BTV) infection, which causes disease mainly in domestic sheep and cattle. Outbreaks involving either BTV serotypes 1 (BTV-1) and 8 (BTV-8) are currently challenging Europe. Inclusion of wildlife vaccination among BTV control measures should be considered in certain species. In the present study, four out of fifteen seronegative Spanish ibexes were immunized with a single dose of inactivated vaccine against BTV-1, four against BTV-8 and seven ibexes were non vaccinated controls. Seven ibexes (four vaccinated and three controls) were inoculated with each BTV serotype. Antibody and IFN-gamma responses were evaluated until 28 days after inoculation (dpi). The vaccinated ibexes showed significant (P<0.05) neutralizing antibody levels after vaccination compared to non vaccinated ibexes. The non vaccinated ibexes remained seronegative until challenge and showed neutralizing antibodies from 7 dpi. BTV RNA was detected in the blood of non vaccinated ibexes from 2 to the end of the study (28 dpi) and in target tissue samples obtained at necropsy (8 and 28 dpi). BTV-1 was successfully isolated on cell culture from blood and target tissues of non vaccinated ibexes. Clinical signs were unapparent and no gross lesions were found at necropsy. Our results show for the first time that Spanish ibex is susceptible and asymptomatic to BTV infection and also that a single dose of vaccine prevents viraemia against BTV-1 and BTV-8 replication.

Characterization of the immune response induced by a commercially available inactivated bluetongue virus serotype 1 vaccine in sheep

The protective immune response generated by a commercial monovalent inactivated vaccine against bluetongue virus serotype 1 (BTV1) was studied. Five sheep were vaccinated, boost-vaccinated, and then challenged against BTV1 ALG/2006. RT-PCR did not detect viremia at any time during the experiment. Except a temperature increase observed after the initial and boost vaccinations, no clinical signs or lesions were observed. A specific and protective antibody response checked by ELISA was induced after vaccination and boost vaccination. This specific antibody response was associated with a significant increase in B lymphocytes confirmed by flow cytometry, while significant increases were not observed in T lymphocyte subpopulations (CD4⁺, CD8⁺, and WC1⁺), CD25⁺ regulatory cells, or CD14⁺ monocytes. After challenge with BTV1, the antibody response was much higher than during the boost vaccination period, and it was associated with a significant increase in B lymphocytes, CD14⁺ monocytes, CD25⁺ regulatory cells, and CD8⁺ cytotoxic T lymphocytes.

Epizootic hemorrhagic disease virus serotype 7 in European cattle and sheep: diagnostic considerations and effect of previous BTV exposure

Epizootic hemorrhagic disease virus (EHDV), an arthropod-borne orbivirus (family Reoviridae), is an emerging pathogen of wild and domestic ruminants that is closely related to bluetongue virus (BTV). The present study examines the outcome of an experimental EHDV-7 infection of Holstein cattle and East Frisian sheep. Apart from naïve animals that had not been exposed to BTV, it included animals that had been experimentally infected with either BTV-6 or BTV-8 two months earlier. In addition, EHDV-infected cattle were subsequently challenged with BTV-8. Samples were tested with commercially available ELISA and real-time RT-PCR kits and a custom NS3-specific real-time RT-PCR assay. Virus isolation was attempted in Vero, C6/36 and KC cells (from Culicoides variipennis), embryonated chicken eggs and type I interferon receptor-deficient IFNAR(-/-) mice. EHDV-7 productively infected Holstein cattle, but caused no clinical signs. The inoculation of East Frisian sheep, on the other hand, apparently did not lead to a productive infection. The commercial diagnostic kits performed adequately. KC cells proved to be the most sensitive means of virus isolation, but viremia was shorter than 2 weeks in most animals. No interference between EHDV and BTV infection was observed; therefore the pre-existing immunity to some BTV serotypes in Europe is not expected to protect against a possible introduction of EHDV, in spite of the close relation between the viruses.

An equine herpesvirus type 1 (EHV-1) expressing VP2 and VP5 of serotype 8 bluetongue virus (BTV-8) induces protection in a murine infection model

Bluetongue virus (BTV) can infect most species of domestic and wild ruminants causing substantial morbidity and mortality and, consequently, high economic losses. In 2006, an epizootic of BTV serotype 8 (BTV-8) started in northern Europe that caused significant disease in cattle and sheep before comprehensive vaccination was introduced two years later. Here, we evaluate the potential of equine herpesvirus type 1 (EHV-1), an alphaherpesvirus, as a novel vectored DIVA (differentiating infected from vaccinated animals) vaccine expressing VP2 of BTV-8 alone or in combination with VP5. The EHV-1 recombinant viruses stably expressed the transgenes and grew with kinetics that were identical to those of parental virus in vitro. After immunization of mice, a BTV-8-specific neutralizing antibody response was elicited. In a challenge experiment using a lethal dose of BTV-8, 100% of interferon-receptor-deficient (IFNAR(-/-)) mice vaccinated with the recombinant EHV-1 carrying both VP2 and VP5, but not VP2 alone, survived. VP7 was not included in the vectored vaccines and was successfully used as a DIVA marker. In summary, we show that EHV-1 expressing BTV-8 VP2 and VP5 is capable of eliciting a protective immune response that is distinguishable from that after infection and as such may be an alternative for BTV vaccination strategies in which DIVA compatibility is of importance.

Identification and differentiation of the twenty six bluetongue virus serotypes by RT-PCR amplification of the serotype-specific genome segment 2

Bluetongue (BT) is an arthropod-borne viral disease, which primarily affects ruminants in tropical and temperate regions of the world. Twenty six bluetongue virus (BTV) serotypes have been recognised worldwide, including nine from Europe and fifteen in the United States. Identification of BTV serotype is important for vaccination programmes and for BTV epidemiology studies. Traditional typing methods (virus isolation and serum or virus neutralisation tests (SNT or VNT)) are slow (taking weeks, depend on availability of reference virus-strains or antisera) and can be inconclusive. Nucleotide sequence analyses and phylogenetic comparisons of genome segment 2 (Seg-2) encoding BTV outer-capsid protein VP2 (the primary determinant of virus serotype) were completed for reference strains of BTV-1 to 26, as well as multiple additional isolates from different geographic and temporal origins. The resulting Seg-2 database has been used to develop rapid (within 24 h) and reliable RT-PCR-based typing assays for each BTV type. Multiple primer-pairs (at least three designed for each serotype) were widely tested, providing an initial identification of serotype by amplification of a cDNA product of the expected size. Serotype was confirmed by sequencing of the cDNA amplicons and phylogenetic comparisons to previously characterised reference strains. The results from RT-PCR and sequencing were in perfect agreement with VNT for reference strains of all 26 BTV serotypes, as well as the field isolates tested. The serotype-specific primers showed no cross-amplification with reference strains of the remaining 25 serotypes, or multiple other isolates of the more closely related heterologous BTV types. The primers and RT-PCR assays developed in this study provide a rapid, sensitive and reliable method for the identification and differentiation of the twenty-six BTV serotypes, and will be updated periodically to maintain their relevance to current BTV distribution and epidemiology (http://www.reoviridae.org/dsRNA_virus_proteins/ReoID/rt-pcr-primers.htm).

Experimental infection of South American camelids with bluetongue virus serotype 8

Bluetongue (BT) is an infectious, non-contagious disease of wild and domestic ruminants. It is caused by bluetongue virus (BTV) and transmitted by Culicoides biting midges. Since 1998, BT has been emerging throughout Europe, threatening not only the naïve ruminant population. Historically, South American camelids (SAC) were considered to be resistant to BT disease. However, recent fatalities related to BTV in captive SAC have raised questions about their role in BTV epidemiology. Data on the susceptibility of SAC to experimental infection with BTV serotype 8 (BTV-8) were collected in an animal experiment. Three alpacas (Vicugna pacos) and three llamas (Lama glama) were experimentally infected with BTV-8. They displayed very mild clinical signs. Seroconversion was first measured 6-8 days after infection (dpi) by ELISA, and neutralising antibodies appeared 10-13 dpi. BTV-8 RNA levels in blood were very low, and quickly cleared after seroconversion. However, spleens collected post-mortem were still positive for BTV RNA, over 71 days after the last detection in blood samples. Virus isolation was only possible from blood samples of two alpacas by inoculation of highly sensitive interferon alpha/beta receptor-deficient (IFNAR(-/-)) mice. An in vitro experiment demonstrated that significantly lower amounts of BTV-8 adsorb to SAC blood cells than to bovine blood cells. Although this experiment showed that SAC are generally susceptible to a BTV-8 infection, it indicates that these species play a negligible role in BTV epidemiology.

Financial evaluation of different vaccination strategies for controlling the bluetongue virus serotype 8 epidemic in The Netherlands in 2008

Background

Bluetongue (BT) is a vector-borne disease of ruminants caused by bluetongue virus that is transmitted by biting midges (Culicoides spp.). In 2006, the introduction of BTV serotype 8 (BTV-8) caused a severe epidemic in Western and Central Europe. The principal effective veterinary measure in response to BT was believed to be vaccination accompanied by other measures such as movement restrictions and surveillance. As the number of vaccine doses available at the start of the vaccination campaign was rather uncertain, the Dutch Ministry of Agriculture, Nature and Food Quality and the Dutch agricultural industry wanted to evaluate several different vaccination strategies. This study aimed to rank eight vaccination strategies based on their efficiency (i.e. net costs in relation to prevented losses or benefits) for controlling the bluetongue virus serotype 8 epidemic in 2008.

Methodology/Principal Findings

An economic model was developed that included the Dutch professional cattle, sheep and goat sectors together with the hobby farms. Strategies were evaluated based on the least cost - highest benefit frontier, the benefit-cost ratio and the total net returns. Strategy F, where all adult sheep at professional farms in the Netherlands would be vaccinated was very efficient at lowest costs, whereas strategy D, where additional to all adult sheep at professional farms also all adult cattle in the four Northern provinces would be vaccinated, was also very efficient but at a little higher costs. Strategy C, where all adult sheep and cattle at professional farms in the whole of the Netherlands would be vaccinated was also efficient but again at higher costs.

Conclusions/Significance

This study demonstrates that a financial analysis differentiates between vaccination strategies and indicates important decision rules based on efficiency.

Colostral antibody induced interference of inactivated bluetongue serotype-8 vaccines in calves

Since its introduction into northern Europe in 2006, bluetongue has become a major threat to animal health. While the efficacy of commercial vaccines has been clearly demonstrated in livestock, little is known regarding the effect of maternal immunity on vaccinal efficacy. Here, we have investigated the duration and amplitude of colostral antibody-induced immunity in calves born to dams vaccinated against bluetongue virus serotype 8 (BTV-8) and the extent of colostral antibody-induced interference of vaccination in these calves. Twenty-two calf-cow pairs were included in this survey. The median age at which calves became seronegative for BTV was 84 and 112 days as assayed by seroneutralisation test (SNT) and VP7 BTV competitive ELISA (cELISA), respectively. At the mean age of 118 days, 13/22 calves were immunized with inactivated BTV-8 vaccine. In most calves vaccination elicited a weak immune response, with seroconversion in only 3/13 calves. The amplitude of the humoral response to vaccination was inversely proportional to the maternal antibody level prior to vaccination. Thus, the lack of response was attributed to the persistence of virus-specific colostral antibodies that interfered with the induction of the immune response. These data suggest that the recommended age for vaccination of calves born to vaccinated dams needs to be adjusted in order to optimize vaccinal efficacy.