Control Tools

• Diagnostics availability

• Commercial diagnostic kits available worldwide

  Commercially diagnostic kits for bluetongue (BT) include competitive and double antigen ELISAs, agar gel immunodiffusion (AGID) and indirect fluorescent antibody tests (IFAT) for the detection of group-specific antibodies, as well as group specific and serotype-specific real-time RT-PCR assays. Serotype-specific molecular assays are currently available for serotypes 1, 2, 3, 4, 6, 8, 9, 11, 12, 15 and 16. A list of diagnostic tests is available here.

  GAPS

  Most commercial serotyping RT-qPCR kits primarily target serotypes historically circulating in Europe and do not cover the full diversity of 36+ known BTV serotypes. Whether genetic drift, reassortment and emergence of novel strains occur, currently available diagnostic kits can no longer match genomes and need timely re-design and optimization.

  Because some diagnostic kits are manufactured on demand, their availability may be subject to extended lead times.

• Diagnostic kits validated by International, European or National Standards

  Currently, no BTV diagnostic kit is listed in the WOAH Register of validated diagnostic assays. Nevertheless, several real-time RT-PCR assays and competitive ELISAs have been validated and are routinely used by national and international reference laboratories.

  GAPS

  A validated assay requires ongoing evaluation to ensure it remains fit for purpose. Every newly emerging strain should be tested to verify that the current set up of the diagnostic kit reliably detect the virus and/or the specific antibodies.

  Biological samples from remote outbreak to include in validation tests could be not easily accessible.

• Diagnostic method(s) described by International, European or National standards

  Diagnostic methods for BT are listed in the WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, chapter 3.1.3 « Bluetongue (infection with bluetongue virus) ». Updated methods for serogroup and serotype identification and and further characterization of BTV are accessible on the website of the European Reference Laboratory for African Horse Sickness and Bluetongue.

  GAPS

  Diagnostic workflows should increasingly incorporate innovative approaches to complement traditional assays. Diagnostic methods could be enhanced with harmonized and validated Next Generation Sequencing protocols. This technology would allow partial or full genome characterization, molecular epidemiology, detection of reassortment events and phylogenetic analyses. In addition, diagnostic methods could include microarray tests, to perform simultaneous detection and typing of BTVs.

• Commercial potential for diagnostic kits worldwide

  The commercial potential for BTV diagnostic kits remains significant due to the expanding geographic distribution of the virus and the resulting need for reliable surveillance tools.

  GAPS

  Pen-side diagnostic kits could be developed for rapid screening of suspected cases.

  Isothermal LAMP PCR diagnostic kits could be developed for a rapid diagnostic in the field. The development and validation of such assays requires access to a broad panel of BTV variants representing different serotypes and topotypes.

• DIVA tests required and/or available

  To date, no commercial DIVA diagnostic tests are available for bluetongue.

  GAPS

  There is a need for DIVA assays. Serological DIVA tests, to be used in combination with DIVA vaccines, would be helpful for international trade of animals and facilitate surveillance in vaccinated populations.

• Vaccines availability

• Commercial vaccines availability (globally)

  Live attenuated vaccines:

  According to the latest online version of the WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, both live attenuated and inactivated BTV vaccines are available for use in ruminants.

  Live attenuated vaccines are relatively inexpensive to produce and often provide a long-lasting immunity after a single dose. However, live attenuated vaccines could carry major drawbacks, including depressed milk production, abortions, transplacental transmission and birth defects. In addition, there is the risk of onward transmission and genetic reassortment (exchange of genome segments) with field strains.

  They are used in some endemic countries, but no live attenuated vaccines are currently authorised in Europe.

  Inactivated vaccines

  Inactivated vaccines are available against several, but not all, BTV serotypes. They are produced by a number of companies in Europe and are generally more expensive to produce than attenuated ones.. They are generally safe but often require two doses and periodic re-vaccination. Production is largely demand-driven, limiting the availability of vaccines ahead of outbreaks.

  Recently, three inactivated vaccines against the newly emerged “north-European” BTV-3 strain have been developed by three pharmaceutical companies.

  Subunit and other novel vaccine platforms have shown promise at experimental level but are not yet commercially available.

  GAPS

  Inactivated vaccines

  Inactivated vaccines are not produced ‘ahead’ of crisis, because it follows demand and vaccination is most of the time on a voluntary basis. It is difficult for vaccine producers to make the large investments in resources, time and funds to develop, test and produce vaccine for a non-existing market.

  Subunit vaccines are not yet commercially available, but have been developed at laboratory scale and concept proven experimentally.

  Other vaccine platforms

  Recent advances in reverse genetics have opened new possibilities for BTV vaccine development. Innovative antigen delivery systems - including recombinant viral vectors, mRNA-based vaccines, Nanostructure-based vaccines, and improved adjuvant formulations — are being explored to enhance immunogenicity and safety.

  Multivalent vaccines would be ideal to increase end-user acceptability and compliance with vaccination programs.

• Marker vaccines available worldwide

  No marker (DIVA) vaccines are currently available. Several next-generation approaches with DIVA potential—including subunit vaccines, virus-like particles, vectored vaccines and genetically engineered live vaccines (e.g. DISC/DISA)—are under investigation but have not yet been deployed at scale.

  Only studies on a limited number of animals are available on scientific public library.

  GAPS

  Need for efficacious and safe DIVA vaccine

  Further work is needed to commercialise experimental vaccine candidates and to develop cross reactive vaccine reagents/ strategies. These approaches would all be amenable to DIVA assay development.

• Effectiveness of vaccines / Main shortcomings of current vaccines

  Live attenuated vaccines are highly effective and provide long-lasting immunity after a single dose. However, animals vaccinated with live vaccines cannot be differentiated from naturally infected ones. Moreover, some live vaccine strains have the potential to cause clinical symptoms, particularly in naïve animals. Transmission and reassortment of live vaccine strains have also been documented in the field. Inactivated vaccines often require two doses 3 to 4 weeks apart to achieve effective protection. The duration of immunity may also be shorter, requiring annual re-vaccination.

  Currently, no DIVA assay is available for inactivated BTV vaccines.

  All of the current monovalent live or inactivated vaccines are type specific. Cross-protection can be generated by serial vaccination with multiple serotype vaccines.

  GAPS

  Develop an inactivated vaccine that provides long-lasting protection against viremia and clinical signs; ideally with a single administration.

  Further studies are needed to explore the mechanism of cross-serotype protection, including the identification of key epitopes and viral antigens involved.

  The role of viral proteins other than VP2 in conferring cross-protection needs further investigation.

  This may lead to development of cross-reactive vaccines, offering protection against multiple serotypes. Such vaccines would be particularly beneficial in areas where multiple serotypes co-circulate

• Commercial potential for vaccines

  Unlike the attenuated BTV vaccine market, where demand is driven by annual vaccination programs in endemic regions, the European inactivated vaccine market is quite cyclical. When a new serotype is introduced in a naive population it causes major clinical damage and demand rises to very high level. During the BTV8 and BTV3 outbreaks, mass vaccination was applied and several millions of doses were required.

  As a result, the unpredictable nature of the commercial market of BTV vaccines represents a significant challenge for manufacturers whose activity is driven by forecasts. In the initial months of the outbreak pressure is put on manufacturers to develop quickly a vaccine against the new serotype and produce it in facilities that are already occupied by other products. Then, demand is demand is quite short lived since the epizootic wave lasts on average 3 years, after which herd immunity is achieved as a result of infection and/or vaccination, and the market disappears.

  Many countries are now moving away from mandatory or even subsidized vaccination and the market is now mostly based on voluntary vaccination. This trend will generalize as a result of the decision of the EU Commission to declassify bluetongue as category D. Vaccine utilization and market size will decrease proportionally.

  Regarding serotypes exotic to Europe, vaccine producer will not develop and produce seeds for all serotypes without funding and market potential.

  GAPS

  Potential ways to overcome market gaps:

  Visibility on willingness of countries to recommend, mandate, subsidize vaccination or not get involved would help manufacturers decide to invest in R&D and production.

  Willingness of countries to build antigen banks as part of preparedness plans

• Regulatory and/or policy challenges to approval

  The European multistrain guideline (EMA/CVMP) streamlines registration of inactivated veterinary vaccines containing multiple strains of antigenically variable pathogens like BTV. It allows a single marketing authorisation for several strains, reducing repetitive submissions. Applicants must provide comprehensive quality data for all strains, demonstrate safety for each strain and their combinations, and justify efficacy through cross-protection or representative strain testing. The dossier must define strain selection, manufacturing consistency, and include a plan for adding new strains. This procedure, however, requires a full data set and takes several years to build, which is not suitable for emerging infectious diseases like exotic BTV serotypes. Several regulatory frameworks exist that allow rapid access to market for emergency situations: -Under Regulation (EU) 2019/6, Article 110 enables Member States to enact emergency measures allowing the exceptional use of veterinary medicinal products without a full marketing authorization, specifically to respond to Union-listed or emerging animal diseases when national health situations demand it. -Regulation (EU) 2019/6 Article 25 provides the basis for registering of veterinary medicinal products in exceptional circumstances (EC), suited to new or re‑emerging infectious diseases posing serious threats to animal/public health. Article 25 grants a conditional marketing authorisation under exceptional circumstances with obligations for data completion, while Article 110 allows Member States to permit temporary emergency use of a product without any marketing authorisation for immediate disease control.

• Commercial feasibility (e.g manufacturing)

  Commercial feasibility is high, but the availability of manufacturing capacity is a challenge in case of sudden surges of demand.

  GAPS

  Visibility and anticipation of demand is necessary to allow producers to find some manufacturing capacity

• Opportunity for barrier protection

  In theory, vaccination may offer an opportunity for barrier protection by creating immunologically protected buffer zones between endemic and free areas, both within and between countries. However, the feasibility of such a control measure is arguable, as its effectiveness may be compromised by the movement of susceptible ruminants. BT endemicity in most European countries makes this approach not feasible.

• Pharmaceutical availability

• Current therapy (curative and preventive)

  No specific antiviral treatment is available for bluetongue. Treatment is limited to supportive care, including non-steroidal anti-inflammatory drugs (NSAID) to reduce pain, fluid therapy and prevention of secondary infections.

  For animals with severe symptoms, euthanasia is advised for ethical reasons.

  Supportive therapy is rarely implemented by farmers and commercial interest in antiviral drug development is minimal.

  GAPS

  Possibility of developing specific antiviral drugs targeting specific viral proteins/functions. Commercial interest is very limited.

• Future therapy

  There is a need of repellent products with long acting efficacy and shorter withdrawal period. Specific antiviral therapy is not expected to have a market.

• Commercial potential for pharmaceuticals

  Very low.

• Regulatory and/or policy challenges to approval

  Not needed.

• Commercial feasibility (e.g manufacturing)

  Currently not applicable.

• New developments for diagnostic tests

• Requirements for diagnostics development

  Several real-time RT PCR methods have been developed and validated to be used in different specimens (blood, tissues and insects)

  Developing new PCR-based assays is not a priority.

  GAPS

  Continuous upgrade of the PCR test could be necessary for newly circulating strains

  Development of pen-side diagnostic kits could be helpful to obtain rapid, specific diagnosis where specialized laboratory equipment lacks.

  Development of isothermal LAMP PCR could be helpful to confirm cases in the field.

  Classical diagnostic methods could be enhanced with harmonized and validated Next Generation Sequencing protocols and microarray tests.

• Time to develop new or improved diagnostics

  Development of new or improved diagnostic assays can be achieved relatively quickly when prioritized. However, the process that requires the most time is the evaluation and validation of the assay using a broad panel of virus strains to ensure sensitivity, specificity, and robustness. Assay validation is essential for guaranteeing high-quality, reliable, and widely accepted diagnostic tools that comply with relevant regulations

  GAPS

  Rapid, field-deployable diagnostic tools for BT remain underdeveloped

  Not all countries have adequate laboratory infrastructure, trained personnel, or quality systems to ensure reliable testing.

• Cost of developing new or improved diagnostics and their validation

  If a company has to develop and validate new or improved diagnostic assays from scratch, the process is time-consuming and associated with substantial costs. Collaboration between diagnostic and research laboratories and commercial manufacturers is essential to pool resources, leverage complementary expertise, accelerate development, and ultimately reduce costs.

• Research requirements for new or improved diagnostics

  Genomic sequences of currently worldwide circulating BTV strains. DIVA vaccines to enable the development of DIVA diagnostic tests availability of field materials (strains and sera) also from remote areas harmonised and validated Next Generation Sequencing protocols and data analysis workflows

• Technology to determine virus freedom in animals

  cELISA is the recommended method to determine virus freedom in animal populations.

  cELISA together with group specific real-time RT-PCR assays are used to assess virus freedom in individual animal, particularly prior to movement.

  Real-time RT-PCR serotyping assays and virus neutralization tests can be performed to determine freedom from a specific serotype.

  GAPS

  Due to the lack of serological DIVA diagnostic tests, it is currently not possible to discriminate between infected and vaccinated animals.

  In addition, prolonged RNA-emia can complicate the assessment of infection status by real time RT-PCR.

  Outdated diagnostic kits/methods could incorrectly determine the animals’ status.

• New developments for vaccines

• Requirements for vaccines development / main characteristics for improved vaccines

  The currently available vaccines have proven efficient in controlling the BT epidemics in the past and in recent years. However, given the circulation of multiple serotypes in the same areas and the annual recurrence of the disease, safe, long-lasting and multiple serotypes vaccines with DIVA capability would be ideal.

  GAPS

  Better understanding of the immune mechanisms, both humoral and cellular, underlying protective immunity development of multiserotypes vaccines would be ideal for controlling the disease.

• Time to develop new or improved vaccines

  Conventional, inactivated vaccines Development and emergency registration of a new serotype in case of emergence can be quite rapid for a vaccine. For serotype 3, several companies were able to bring a product on market in about 6 months from the moment they accessed a virus isolate. ‘Next generation’ vaccines Vaccines developed using specific biotechnological processes (e.g. recombinant DNA technology and controlled gene expression) are subject to the mandatory EU centralised marketing authorisation procedure under Regulation (EU) 2019/6, requiring assessment by the European Medicines Agency (EMA). Although the centralised procedure is generally more complex than a purely national authorisation, regulatory tools such as authorisation under Exceptional Circumstances (Article 25 of Regulation (EU) 2019/6) may allow rapid approval during emergency situations. Three vaccines against BTV were authorised under this framework in the last two years, with an average time for authorization of 3.5 months, indicating that this procedure may be effective in outbreak situations. Once a marketing authorisation is granted for a given technological platform, subsequent adaptations to additional serotypes may potentially be faster than for traditional inactivated vaccines.

  GAPS

  Access to isolates is a challenge. In link or not with constraints of the Nagoya Protocol, manufacturers are finding it more and more difficult to source isolates from countries, who either are not willing to share or are expecting unrealistic financial contributions. Facilitated access to exotic BTV strains (European biobank), would encourage manufacturers to anticipate first steps of development.

• Cost of developing new or improved vaccines and their validation

  Highly variable depending on technology and availability of existing platform. Can range from a few million Euros to develop add a new serotype to an inactivated vaccine platform, to 20-30 million for the development of a new innovative platform for multiple serotypes

  GAPS

  Entry ticket for newcomer becomes higher and higher as more serotypes co-circulate, requiring combo vaccines.

• Research requirements for new or improved vaccines

  Further research is needed to develop vaccines that induce broader, cross-serotype protection, have DIVA potential and prevent the development of viraemia as well as protecting animals from clinical disease. Advances in molecular virology, together with deeper knowledge of the BTV genome and viral proteins, offer new opportunities to design innovative vaccine concepts. Efforts should focus both on developing new vaccines and on improving existing ones to achieve broader and longer-lasting protection.

  GAPS

  Different vaccine platforms against BTV should be explored, including plant-based, subunit, DISA/DIVA, mRNA, saRNA, pDNA, and DREP vaccines. Ideally, these efforts should aim to identify target proteins or epitopes capable of conferring cross-protection against multiple serotypes.

• New developments for pharmaceuticals

• Requirements for pharmaceuticals development

  None anticipated at present.

• Time to develop new or improved pharmaceuticals

  Not applicable.

• Cost of developing new or improved pharmaceuticals and their validation

  Not applicable.

• Research requirements for new or improved pharmaceuticals

  None at present apart from new methods of vector control both in terms of killing vectors but also preventing vectors form attacking hosts.

Disease details

• Description and characteristics

• Pathogen

  Bluetongue virus (BTV) is a viral species within the genus Orbivirus, family Sedoreovirdae. The virus is non-enveloped, approximately 80 nm in diameter, and composed of three concentric protein layers enclosing a genome of ten linear segments of double-stranded RNA (dsRNA). The genome segments encode for 7 structural proteins (VP1-VP7) and 5 non-structural proteins (NS1-NS5). All BTV isolates share common group-specific antigenic determinants, primarily associated with the highly conserved core surface protein VP7. Antibodies against VP7 form the basis of most serogroup-specific ELISA assays used for surveillance and diagnosis. In contrast, the outer capsid protein VP2 is highly variable and represents the principal determinant of serotype specificity. To date, more than 36 BTV serotypes or genotypes have been described worldwide, although only serotypes 1–24 (“classical” serotypes) are regulated under national and international animal health legislation. Beyond serotype classification, BTV isolates can be grouped into distinct geographical lineages, or topotypes, broadly classified into at least eastern and western topotypes, with further regional sub-grouping. These genetic differences reflect long-term virus evolution within specific ecological systems and vector populations.

  GAPS

  Much has been done in identifying the mechanisms involved in cell binding and initiation of infection, BTV replication, virus assembly and packaging, control of differential protein expression in mammalian and insect cells, virus release and transmission at the molecular, cellular and whole organism level. However, important knowledge gaps remain, including the precise identification of host cell receptors involved in virus attachment and entry, and the structural basis of cross-reactivity and cross-protection among serotypes. Further research is required to: define the atomic structure–function relationships of outer capsid proteins from representative serotypes and topotypes; identify conserved epitopes that may support the development of cross-protective vaccines; characterise the biological significance of atypical BTV serotypes, particularly their possibility to reassort with classical serotypes, and assess the potential epidemiological and biological consequences of such events. determine the mechanisms at the basis of overwintering and virus persistence determine the genetic basis of virulence between and within serotypes.

• Variability of the disease

  BTV exhibits marked biological and epidemiological variability, which reflects a combination of virus strain–specific factors and host-related determinants. In ruminants, infection induces a strong neutralising antibody targeting VP2, that is protective but largely serotype-specific. In parallel, the host also mounts an immune response against more conserved core and non-structural proteins, generating cross-reactive immunity that could contribute—at least partially—to protection against clinical disease. This broader protection likely involves both humoral and cell-mediated immune mechanisms. Because transmission depends on biting midges, bluetongue displays seasonal patterns in temperate regions and more continuous circulation in tropical and subtropical areas. In recent decades, several western topotype strains (e.g. BTV-1, -3, -4 and -8) have successfully expanded into northern and central Europe, demonstrating efficient transmission by local Culicoides species, particularly those belonging to the C. obsoletus complex. In contrast, other strains—including eastern topotypes of BTV-1, 4, 9 and 16, as well as western BTV-2 and certain strains of western BTV-4 have remained largely confined to southern Europe, with no substantial northward expansion observed to date. The simultaneous circulation of multiple serotypes and topotypes creates favourable conditions for genome reassortment, a frequent event in BTV evolution that can generate viruses with altered virulence, host range or vector competence. Additionally, some of the newly described “atypical” BTV serotypes—most notably BTV-26 and BTV-27—are capable of direct host-to-host transmission, independent of midge vectors. These serotypes are unable to replicate in Culicoides-derived cells, and reverse genetics has identified specific genome segments of BTV-26 that restrict replication in insect cells, providing insights into the determinants of non-vector transmission.

  GAPS

  Comprehensive whole-genome sequencing and comparative analyses are needed to resolve the global diversity and distribution of BTV serotypes and topotypes. Such data are essential to understand the biological significance of genetic variation—including segment reassortment—on virus replication in the mammalian host, infection dynamics in different Culicoides vectors and the efficiency of transmission between hosts and vectors. The mechanisms that determine why certain BTV strains emerge, persist, shift in geographic distribution, or show enhanced transmissibility remain poorly understood. Studies integrating reverse genetics, vector competence assays, and phylogeography are required to define the genomic constraints and adaptive signatures associated with the observed geographical clustering of BTV strains. The precise mapping of neutralising epitopes on VP2 and VP5 is incomplete or lacking for most serotypes. Although evidence indicates the existence of cross-reactive neutralising sites, their identity and immunological relevance remain unresolved. Defining these epitopes would support the design of cross-serotype or broadly protective vaccines, including subunit and VLP-based platforms. The nature and role of T-cell–mediated immune responses during BTV infection are still not fully elucidated. Their contribution to protection against homologous versus heterologous strains or topotypes remains particularly unclear. Detailed immunological studies are needed to define the mechanisms underpinning cross-protection and disease modulation. Reverse genetics technologies offer powerful tools to dissect the genetic basis of key viral traits, such as virulence, transmissibility, serotype specificity, temperature dependence, and vector competence. These approaches should be expanded to identify viral genomic elements that modulate interactions with both vertebrate hosts and insect vectors. There is a continued need to generate and publish high-quality complete genome sequences from well-documented BTV isolates across world regions. Such datasets are essential for tracking molecular epidemiology, evolutionary dynamics, reassortment events, and transboundary strain movements, and for establishing robust reference sequences for all ten genome segments of major BTV lineages and topotypes.

• Stability of the agent/pathogen in the environment

  BTV is very stable. It survives for decades in blood stored at under -70˚C, although the process of freezing and thawing will itself reduce the titre of virus. In a paper by Puggioni et al. (2018), a BTV-1 infected blood sample collected from an ewe with BT clinical signs during the 2006 Sardinia outbreak and stored in the fridge at + 4°C, was able to cause clinical signs when inoculated in a ram 10 years later. BTV is inactivated by 50°C/3 hours and 60°C/15 minutes. It is sensitive to pH <6.0 and >8.0, and is inactivated by ß-propiolactone, iodophores and phenolic compounds. The virus survives as long as 60 days in the circulation after infection of a ruminant, and infection persists life-long in vector insects. The virus apparently survives freezing winters. However, the mechanism behind this survival or ‘over-wintering’ remains unknown although vertical transmission in the mammalian host has been demonstrated and may contribute. It has been proposed that BTV “overwinters” in temperate areas through low level circulation of the virus in vectors, including infected adult insects that survive for relatively long periods even in winter. There is also some evidence for detection of BTV RNA in Culicoides larvae collected in the field from outbreak sites in North America. This suggests that in some cases the virus may be transmitted vertically in the insect vector. However, attempts to recover infectious virus were unsuccessful and the epidemiological significance of these observations is uncertain.

  GAPS

  Understanding the over wintering mechanism(s) in the host, vector and/or environment, including potential differences between species and distinguished ecological zones.

• Species involved

• Animal infected/carrier/disease

  Bluetongue virus infects a wide range of domesticated, zoo and wild ruminants including sheep, goats, cattle, South American camelids, buffalo, bison, deer, antelope, bighorn sheep and North American elk. Among domestic ruminants, clinical disease occurs most frequently in sheep and occasionally in goats and cattle. Severe disease also occurs in some wild ruminants, especially white-tailed deer (Odocoileus virginianus). Disease has also been described in an extensive variety of non-African ungulates in zoos in Europe, and in South American camelids present in the UK, France, Germany and USA. Some carnivores have antibodies to bluetongue, and fatal disease has been described in lynx and dogs.

  GAPS

  The role of wildlife species in the persistence of BTV in the environment has not been deeply studied. Understanding the over-wintering mechanisms, with emphasis on investigating the role of reservoir and vertebrate hosts in virus persistence

• Human infected/disease

  BTV does not infect humans.

• Vector cyclical/non-cyclical

  Biological transmission is primarily mediated by Culicoides biting midges. Vector competence varies among species and regions, influencing local transmission dynamics.

  GAPS

  Impact of different Culicoides species involved in BTV transmission across different ecoregions.

  Investigation on direct contact transmission, especially for atypical BTV serotypes

• Reservoir (animal, environment)

  Cattle are the main amplification hosts of BTV, as they remain viremic for a longer period compared to other species. Sheep and other ruminants also serve as sources of virus for transmission. In the last two decades, alongside the classical 24 serotypes which are transmitted by vectors, novel serotypes have been identified. They are characterized by causing asymptomatic or subclinical infections. Some of them being directly transmitted, exhibiting prolonged viraemia and using goats and sheep as reservoir hosts (small ruminants- adapted strains).

  GAPS

  Further investigation is needed to understand the mechanism(s) of BTV overwintering, including the potential role of insects and vertebrates in maintaining the virus during inter-epizootic periods.

• Description of infection & disease in natural hosts

• Transmissibility

  The primary and most relevant route of BTV transmission between susceptible ruminants is via the bites of infected adult female biting midges of the genus Culicoides, that act as biological vectors. Consequently, the geographical distribution of BTV is largely determined by the distribution and ecology of these vectors.

  However, there is limited evidence of oral infection/transmission between animals kept in close proximity in confined spaces, but its epidemiological significance is considered very low.

  Trans-placental infection has been documented with laboratory adapted strains, as well as with certain field strains, such as the North-European BTV-8 and BTV-3 strains. A minimally passaged BTV-2 field strain (one passage on KC cells followed by a single passage on mammalian cells) has been shown to cross the placental barrier in experimentally infected ewes and infect offspring. Similarly, a BTV-1 passaged in vitro caused abortion in experimentally infected pregnant ewes.

  Atypical serotypes such as BTV-26 and BTV-27 have been shown to be transmitted by direct contact rather than vectors. BTV-26 and 27 do not replicate in Culicoides-derived Kc cells, and reverse genetics has identified the genome segments responsible for restricting replication in these cells.

  The proteases present in saliva from adult Culicoides can modify the outer capsid proteins of the virus, enhancing its infectivity for the vector insect and removing its hemagglutination activity. These changes and enzymes may therefore play a significant role in the infection processes in both the insect and mammalian host.

  GAPS

  A better understanding is needed of the processes and mechanisms which underlie transmission by arthropod vectors, including factors that promote or limit transmission/vector competence with specific virus strains.

  Culicoides saliva contains a large number of uncharacterised proteins, including enzymes (e.g. proteases) and inhibitors. The specific role of these proteins in BTV infection, transmission, and virus–host interactions require a more detailed investigation.

  Identify the viral genetic determinants involved in the transplacental transmission of minimally passaged BTV field strains, to clarify why certain strains cross the placental barrier while others do not.

  Determine whether viraemic newborns contribute to BTV spread or overwintering

  Investigate the potential role of oral transmission, including infection via colostrum or placental tissues, in both the spread and overwintering of BTV.

  Determine the relative importance of short-distance (local) spread compared with long-distance dissemination, and identify the ecological and epidemiological factors influencing each mode of spread.

  During outbreaks, assess the proportion of transmission attributable to wind-borne dispersal of infected Culicoides compared with spread due to animal movement, considering geographic and climatic variability across different regions of Europe and globally.

• Pathogenic life cycle stages

  Throughout its life cycle, BTV infects both arthropod vectors and vertebrate hosts. In classical bluetongue epidemiology, the virus follows a vector-host- vector cycle. Culicoides midges acquire the infection when feeding on a viraemic ruminant host. After the extrinsic incubation period, the infected vector is able to transmit the virus back to susceptible animals during blood meals. For some of the newly identified, small-ruminant–adapted serotypes - notably BTV-26 and BTV-27—a direct host-to-host transmission cycle has been proposed, representing a deviation from the classical vector-borne pattern.

  GAPS

  Assess the vector competence and capacity of different Culicoides species for diverse BTV serotypes, and determine the factors influencing successful transmission. Better investigate the infection dynamics of atypical BTV serotypes, including incubation period, routes of infection, viraemia profiles, host immune responses, and patterns of virus excretion.

• Signs/Morbidity

  Most BTV infections are clinically inapparent. However, a proportion of infected sheep and, occasionally, other ruminants may develop moderate to severe disease. The severity of clinical signs depends on multiple factors, including:
  • Virulence of the BTV serotype/strain;
  • Breed and species of the host;
  • Immune status and prior exposure;
  • Overall naivety of the population.
  Clinical disease is most frequently observed in sheep. However, cattle and goats can still develop significant pathological consequences. In most cases, infection in wild animals—especially wild European deer—remains undetectable: they are infected (viraemia or antibodies) but do not develop any visible symptoms of the disease. Acute form (sheep, cattle, goats and some species of deer) Fever (up to 42°C), depression, inflammation, haemorrhages (particularly in the skin), ulceration, erosion and necrosis of the oral mucosa, swollen and sometimes cyanotic tongue, conjunctivitis, nasal serous to mucopurulent nasal discharge, lameness due to coronitis, respiratory distress, severe pulmonary oedema, serous effusions and subcutaneous and intermuscular oedema. Death in a proportion of infected animals. Abortion of severely affected animals (often without virus-infection of the foetus) Can be teratogenic in cattle and sheep (depending on strain), and can lead to dummy calf syndrome. Early embryonic loss and decreased reproductive efficiency is a more frequently seen manifestation of the disease in cattle and can be devastating to their calf/milk production. Clinical signs in cattle also include hyperaemia and necrosis of the muzzle (“burnt muzzle”).

  GAPS

  Genomic determinants of virulence remain incompletely understood. Why are some strains of BTV more pathogenic than others?

• Incubation period

  Animals can become viraemic starting at 3-4 days post-infection, but the incubation period both in sheep and cattle is usually 5 to 10 days.

• Mortality

  In sheep, the severity of disease varies widely depending on several factors, including breed, immune status, virus strain and environmental stresses. The morbidity rate can be as high as 75% in sheep, while mortality rate is usually 0-20%. In contrast, most infections in cattle and goats are clinically unapparent. However, cattle infected with certain BTV strains – notably the BTV-8 and 3 strains present in North Europe - may develop clinical signs, although death remains rare. When disease does occur, affected cattle may experience eye redness, drooling, hyperemia and erosions of oral mucosa and muzzle, lameness, drop in milk yield and reduced body condition. Virulence in BTV appears to be multigenic, with several viral genome segments identified as key determinants of pathogenicity. Some of these segments have been experimentally demonstrated to function as major virulence factors. Notably, the European BTV-8 strain identified at the start of the 2006 northern European outbreak exhibited higher virulence than strains isolated toward the end of the epizootic or the strain that re-emerged in France in 2015. These observations support the association between genetic variability within the BTV population and changes in virulence. There is evidence that Culicoides cells may act as an “incubator” in which viral variants emerge and evolve. The atypical BTV serotypes present a different pattern: although their morbidity can exceed 70%, infections in goats and sheep are generally asymptomatic, indicating a markedly different host–virus interaction.

  GAPS

  Expand the current understanding of the host and viral factors that determine the severity and clinical manifestations of BTV infection in different ruminant species. Investigate why certain BTV strains are consistently more virulent than others in cattle and sheep, including the underlying genetic determinants and their interaction with the host immune system. Elucidate the mechanisms underlying the relative resistance of ruminants living in endemic areas for a very long time compared to naive ruminants, and assess the roles of innate immunity, adaptive responses, and co-evolution with local BTV strains. Investigate whether the introduction of exotic BTV strains into endemic regions leads to more severe disease in local breeds (as observed in India and Europe), and determine whether this is associated with differences in virus topotype, leading to reduced cross-protection mediated by non-neutralising antibodies or cell-mediated immunity.

• Shedding kinetic patterns

  Although BTV RNA can be detected in the blood of cattle and sheep by real-time RT-PCR for several months post-infection, animals are usually infectious to competent Culicoides vectors for only a limited period of maximum a few weeks, but usually much shorter. According to the WOAH, the infectious period can extend up to 60 days post-infection, although most animals remain vector-infectious for a shorter duration. Notably, studies with BTV-8 have shown that the infectious dose not significantly affect either the duration or magnitude of viraemia. The epidemiology of atypical BTV serotypes (BTV-25, BTV-26 and BTV-27) in goats differs markedly from that of classical serotypes (BTV-1 to BTV-24), as these infections may not involve Culicoides vectors. Recent evidence indicates that direct contact transmission, likely via aerosol, occurs between livestock for BTV-26 and BTV-27. Furthermore, BTV-25 viral RNA has been detected in individual goats for up to two years, with some animals maintaining infectious blood for 12–19 months, suggesting prolonged viraemia and potential long-term virus maintenance in the host.

  GAPS

  Determine the infectious period and the duration of detectable viral RNA by molecular methods under natural environmental conditions across different ruminant species and BTV serotypes. Investigate how long sheep and cattle remain infectious to vectors according to the serotype involved in infection. Identify host genetic factors that may influence the duration of viraemia and infectiousness, including immune response genes or other host traits affecting viral clearance. Explore BTV genetic factors that control the length of the infectious period, including genome segments or sequence variants that modulate viral replication, persistence, or immune evasion.

• Mechanism of pathogenicity

  Following infection via the bite of an infected vector, BTV initially replicates in endothelial cells and skin-resident immune cells. Viral replication in target cells triggers both innate and adaptive immune responses, which contribute to the initial clearance of the virus and the development of long-term resistance against homologous serotypes. After initial replication, infection, BTV spreads to the regional lymph nodes and then subsequently disseminates through bloodstream to secondary replication sites before entering the bloodstream. Replication in small vessels leads to damage of endothelia and consequently to macroscopic lesions such as edema, diffuse haemorrhages, ulcers and necrosis. Replication of BTV in target cells triggers the immune response, leading to the clearance of the virus.

  GAPS

  Investigate the contributions of the innate and acquired immune responses to both virus clearance and disease pathogenesis, including how these responses influence viraemia, tissue damage, and cross-protection. Define the role of Culicoides saliva in modulating the initiation, dissemination, and severity of infection in the mammalian host, including its effects on local immune responses and viral replication kinetics. Identify and characterise the cell types and tissues that may support transient viral persistence, contributing to extended viraemia, subclinical infection, and potential overwintering.

• Zoonotic potential

• Reported incidence in humans

  Bluetongue is not a zoonotic disease.

• Risk of occurence in humans, populations at risk, specific risk factors

  None

• Symptoms described in humans

  Not applicable

• Likelihood of spread in humans

  None

• Impact on animal welfare and biodiversity

• Both disease and prevention/control measures related

  Clinical BT, especially in severe cases, has a clear impact on animal welfare due to listlessness and pain associated with oral and podal lesions.

  Control measures, such as movement restrictions and vaccination, have a negligible impact on animal welfare.

  GAPS

  Data gaps remain regarding the assessment of the full impact of bluetongue on animal welfare, particularly with respect to subclinical infections.

• Endangered wild species affected or not (estimation for Europe / worldwide)

  A large variety of wild species can be affected by BTV. These include some species of cervids (mainly white-tailed deer in north-America and other wild ungulates such as yaks and bisons. However, BTV impact on wild populations is negligible in the long-term.

  GAP

  The role of wildlife in BTV emergence and persistence is not fully understood.

• Slaughter necessity according to EU rules or other regions

  As a vector-borne disease, and except for welfare reasons, there is no justification for culling BTV-infected animals. According to EU regulations, the slaughter of animals affected by BTV is not recommended. In the UK, however, initial culling of infected animals was implemented following the BTV-3 outbreaks.

• Geographical distribution and spread

• Current occurence/distribution

  BTV is endemic in Africa, Asia, northern Australia, the Americas, and more recently, in areas in Europe.

  GAP

  Monitoring in endemic countries is not usually implemented, due to the scarce importance of the disease.

• Epizootic/endemic- if epidemic frequency of outbreaks

  In tropical regions, outbreaks usually occur throughout the year, often caused by different serotypes. The disease shows a seasonal pattern in temperate regions, with outbreaks usually reported in late summer and early autumn. In recent years, significant outbreaks caused by BTV-8 and BTV-3 have been reported in Europe. In the future, climate change—characterized by hotter periods lasting longer—is likely to exacerbate the epidemiological situation by expanding vector activity and transmission windows

• Seasonality

  Seasonal cycle related to the movement life cycle and seasonal abundance of the adults of Culicoides vectors. Culicoides peaks depend on season, local meteorological conditions and species involved. Culicoides abundance is also linked to livestock density and land use. Atypical BTV (at least BTV-26 and BTV-27) occurrence is not related to seasons

  GAP:

  Factors involved in vector survival throughout the winter period, and their re-emergence during the vector season (usually summer).

• Speed of spatial spread during an outbreak

  The speed of spread during an outbreak varies largely depending on several factors, such as species, animal density, serotype, etc. Wind could play an important role in BTV spreading over short and long distances (even over sea).

  GAP

  Investigate the speed of spatial spread of BTV depending on the different transmission modes under varying meteorological and environmental conditions.

• Transboundary potential of the disease

  BTV has a huge potential to spread beyond the areas of first emergence or re-emergence.

  Many outbreaks in the past have proven that BTV can spread extensively both through animal movements and vectors over long distances. Past and recent outbreaks (e.g., BTV-3 in Northern-Europe 2023-2025) demonstrates that the disease knows no borders.

  In addition, it has been reported that infected Culicoides can be transported by wind for long distances, even trans-continentally. This hypothesis can explain the recent outbreaks of BTV-3 and BTV-5 in Sardinia (Italy), following the viral circulation in Northern Africa.

  GAPS

  Monitoring the viral circulation in Sub-Saharan and Northern-African Countries could help in improving the preparedness of European countries to the emergence of new serotypes.

• Route of Transmission

• Usual mode of transmission (introduction, means of spread)

  The usual route of BTV transmission to its ruminant hosts is via the bites of virus-infected haematophagous Culicoides midges that act as biological vectors of the virus. Vector midges play a crucial role to the natural epidemiology and spread of BTV. Midges of certain species in the genus Culicoides transmit BTV between susceptible ruminants, having become infected by feeding on viraemic animals (the vertebrate host). After a replication period of 6–8 days in the insect’s salivary glands (development time being dependent upon temperature) the virus can be transmitted to a new vertebrate host during feeding. Infected midges remain infective for life. Infection of the midge is a relatively inefficient process with less than ~10% of insects that ingest a viraemic blood meal becoming infected. An even lower percentage may become fully infected and capable of transmitting the virus, depending on the insect vector species. However, transmission of virus from a fully infected insect to mammalian host is an efficient process (possibly up to 100% efficient). This may help to explain the transmission of virus by wind borne insects over large distances. Vector midges can fly short distances of 1- 2 km, but they can be blown much farther by wind. Long distance spread of BTV from endemic regions to adjacent uninfected areas can occur via the wind-borne dissemination of virus-infected midges, especially over water. The movement of BTV-infected animals can be responsible for translocation of BTV, however, such occurrences are only important if the local vector population within the receiving region is able to efficiently acquire and transmit the introduced virus.

• Occasional mode of transmission

  The epidemiological importance of vector-independent transmission of BTV is largely unknown, but it clearly can occur. Below there is a list of documented vector-independent transmission routes: -transplacental transmission: it has been demonstrated for the “north-European” BTV-8 and BTV-3 strain as well as for some other strains. Moreover, this route of transmission has been proven for live attenuated vaccine strains -direct contact transmission of BTV-26, likely by aerosol, between livestock -the occasional occurrence of venereal transmission from infected male ruminants to females and, subsequently, to offspring. -oral transmission to ruminants (e.g., eating infected placenta and to carnivores (consumption of infected meat)

  GAP

  Deeper insights into the epidemiological significance of vector-independent transmission.

• Conditions that favour spread

  Presence and abundance of Culicoides vectors and high livestock density in an area. High temperature and relative humidity, wind conditions which can blow the vector into new areas. Animal movements.

• Detection and Immune response to infection

• Mechanism of host response

  The immune response to BTV infection is complex and involves multiple components, including humoral immunity (both neutralizing and non-neutralizing antibodies), cell-mediated immunity and inflammatory processes. Immunity—whether naturally acquired after infection or induced by vaccination—tends to be serotype-specific; protection against one serotype is often ineffective or only partially effective against heterologous serotypes, depending on serotypes involved. In naturally infected animals, immunity is generally considered to be long-lasting, potentially lifelong BTV has been shown to persistently infect ovine γδ T-cells in vitro, a phenomenon that may also occur in vivo and could represent a mechanism contributing to long-term viral persistence in the mammalian host and thus overwintering. The virus can also infect dendritic cells and other immune cell populations, which may facilitate viral dissemination within the host through trafficking to lymphoid tissues and the bloodstream. During infection, host protease enzymes associated with inflammation can cleave viral surface proteins, generating infectious sub-virus particles with significantly enhanced infectivity—up to 100-fold higher—for Culicoides vectors. This mechanism may play a critical role in amplifying transmission efficiency.

  GAPS

  Improve understanding of host immune responses to BTV, including the identification of correlates of protection in vaccinated animals, mechanisms of immune evasion and the role of host immunity in disease pathogenesis. Enhance knowledge of immune responses relevant to vaccination strategies, particularly the identification of viral epitopes involved in serotype-specific and cross-reactive immune responses and protection. Deeper knowledge of cell-mediated immunity in protection against BTV and define the mechanisms through which it contributes to viral clearance and disease modulation. Identify the viral proteins and epitopes involved in protective cell-mediated immune responses, and understand their variability among serotypes and strains. Characterize the signalling pathways activated during BTV infection and/or vaccination, to better understand host immune activation and viral interference mechanisms.  Deeper knowledge on the antiviral mechanisms in the insect vector. Determine whether acquired immune mechanisms develop in Culicoides during BTV infection, and assess their relevance for vector competence, viral persistence, and transmission dynamics.

• Immunological basis of diagnosis

  Neutralizing antibodies against VP2 can be detected by seroneutralisation test. Antibodies against VP7 are detected in the current commercial ELISA tests. Antibodies against other conserved viral proteins could also serve as a basis to indicate a previous infection. Cellular immune responses against NS1, VP2, VP3, VP5 and VP7 have been observed.

  GAP

  Development of serotype-specific ELISA assays.

• Main means of prevention, detection and control

• Sanitary measures

  The most important sanitary measure to avoid the introduction of BTV in a free area is the pre-movement testing of animals and/or germinal products.

  Vector control and surveillance are also key to control the spread of the disease.

  Prompt reporting of BT outbreaks and appropriate serological and entomological surveillance and monitoring programme are strongly recommended.

  Vaccination is the pillar of BT prevention

  GAPS

  Development of safe and efficacious vaccines against BTV serotypes likely to e introduced in free areas. Development of cross-protective vaccines is ideal for disease prevention and control.

• Mechanical and biological control

  The main measures to control and eradicate the disease include restriction of animal movements from affected areas to non-infected regions and the use of vaccines. Vector control has sometimes been advised, but evidence suggests that the use of insecticide and insect-repellent as well as protective nets are generally inefficient in preventing disease spread. Restriction of movements of live ruminants can help limit outbreaks, but this approach is sometimes not feasible or cost-effective. Vaccination remains the most important and effective measure for controlling bluetongue and preventing its spread.

• Prevention through breeding

  Control of Bluetongue through breeding involves selecting and propagating livestock with natural resistance to BTV infection or milder disease outcomes. Certain breeds, particularly indigenous African sheep and cattle, exhibit greater tolerance to infection, developing subclinical or less severe disease. By favouring these traits in breeding programs, herds can become more resilient to outbreaks, reducing morbidity, mortality, and economic losses. This approach does not prevent infection or virus circulation but serves as a complementary strategy to vaccination and vector control, especially in endemic regions. At present, this strategy is not feasible and has very little interest, as it would require long-term breeding programs and significant investment. Currently, it is considered impractical and is not implemented in Bluetongue control plans.

  GAPS

  There is limited knowledge about the genetic basis of resistance to BTV in different ruminant breeds. It is unclear whether selecting for resistant animals would significantly reduce virus circulation or outbreak severity.

• Diagnostic tools

  Currently, several group specific and serotype-specific real time RT-PCR are available for the detection of viral nucleic acid. Serological diagnosis can be conducted using ELISA and virus-neutralization tests applied to sentinel animals and for the analysis of paired sera samples. For virus isolation assays, protocols are based on a primary isolation in embryonated eggs or insect cells (Aedes albopictus clone C6/36 or Culicoides sonorensis derived KC or CuVa cells), followed by passages in mammalian cell lines (such as BHK21 or Vero). cELISA based on conserved VP7 protein are used to detect specific serogroup antibodies, whilst virus neutralization assays allow to identify the serotype-specific neutralising antibodies and their titre.

  GAPS

  RT-PCR techniques can detect RNA-emia for extended periods, even after the virus is no longer infectious. False negatives may be caused by the inability of a test that is not properly updated to identify novel or reassortant strains. The widest range of viral strains and field samples should be included in the development of new diagnostic methods and kits, as well as in their validation. DIVA tests in combination with DIVA vaccine, harmonised and validated Next Generation Sequencing protocols and data analysis workflows, pen-side tests, LAMP PCR and microarray tests are next steps in diagnostic tools development.

• Vaccines

  Although several vaccine strategies have shown promising results experimentally, inactivated vaccines remain the only commercially produced and widely used vaccines to prevent bluetongue. When vaccinating against BT, the serotypes included in the vaccine must match those circulating in the field. Since the first BT outbreaks in the European Union, different vaccines have been used depending on the country and serotype. For example, during the initial outbreaks in France, sheep were vaccinated with live attenuated vaccines against serotypes 2, 4, and 16, whereas in Spain vaccines against serotypes 2 and 4 were used. In Italy, from 2002 to 2005, domestic ruminants (cattle, goats, and sheep) were vaccinated with live attenuated vaccines targeting serotypes 2, 4, 9, and 16. However, despite these drawbacks, live attenuated vaccines, if produced and used properly, can successfully control and, in some circumstances (Balearic Islands, Corsica), eradicate the infection. These vaccines have been used successfully for many years to protect animals in endemic areas (e.g. in Southern Africa). Although live attenuated vaccines can be highly effective, they have certain drawbacks: They may revert to virulence or be inherently virulent in naïve populations. They can induce abortion in pregnant animals. Vaccinated animals can develop viraemia, allowing the vaccine virus to circulate in Culicoides populations. The vaccine virus may undergo reassortment with circulating field strains of different serotypes. As an alternative, inactivated vaccines against BTV-2 and BTV-4 became available in 2005–2006. From 2007–2008, inactivated vaccines against BTV-1, BTV-8, and BTV-9 were introduced, leading to mass vaccination campaigns in many EU countries against BTV-8 and BTV-1, which proved highly successful. Vaccination was also effective during recent BTV-4 incursions. In recent years, however, vaccination in many countries is now primarily used to enable safe animal movements. Recently, inactivated vaccines against BTV-3 has been developed by three pharmaceutical companies, and have been used in those countries where this serotype have been circulating. Notably, no inactivated vaccines against the newly emerged BTV-5 are currently available. “Next-generation” vaccine strategies—many with DIVA (Differentiating Infected from Vaccinated Animals) capability—have not yet reached the market or undergone large-scale testing. These include: Non-replicating subunit vaccines and virus-like particles (VLPs). Heterologous microbial expression vectors, such as poxviruses expressing immunogenic BTV proteins. Genetically engineered live attenuated vaccines, including replicating but non-transmissible virus-based vaccines (DISC and DISA).

  GAPS

  Development of vaccines that protect against multiple serotypes, to be used in areas where more than one serotype circulates. Identification of viral epitopes involved in type specific and cross-reactive immune protection. Further understanding is needed of the significance of strain/topotype variation in the specificity, efficacy of neutralizing antibody and cell mediated responses. More work is required in the development / evaluation of novel / appropriate antigen delivery platforms / adjuvants.

• Therapeutics

  No specific treatment is available, other than supportive care.

• Biosecurity measures effective as a preventive measure

  Restriction of animal movements from infected to free regions or zones, particularly during periods of peak vector activity. Vector control measures aimed at reducing exposure to Culicoides midges through the use of insecticides and repellents. Good farm practices aimed at limiting vector breeding sites Use of of insect-proof or fine-mesh screens in animal housing combined with the application of residual insecticides to animal premises. Indoor housing at night. Mechanical ventilation to increase air movement within barns. Surveillance - both passive and active - and early detection. Entomological surveillance Testing of animals introduced from non-BTV-free areas or regions prior to movement Since BT is a non-contagious disease, isolation and culling of infected animals are generally not effective or proportionate control measures.

  GAPS

  Evaluate the true effectiveness of sanitary measures as a preventive measure.

• Border/trade/movement control sufficient for control

  Pre-movement or pre-introduction testing of animals is a key measure to prevent the introduction of bluetongue virus into BTV-free regions or zones.

• Prevention tools

  None at the moment.

• Surveillance

  Both passive and active surveillance programs should be implemented to confirm or exclude BTV circulation and enable a rapid response upon detection. Susceptible hosts should be tested before movement. Entomological surveillance is also essential for an effective control program.

  GAPS

  Limited collaboration with endemic countries where multiple serotypes circulate and which are not yet present in Europe Need for up-to-date diagnostic tests capable of detecting strains and serotypes that may emerge based on epidemiological data and risk analysis Need for up-to-date diagnostic tests capable of detecting strains and serotypes that may emerge, guided by epidemiological data and risk analysis.

• Past experiences on success (and failures) of prevention, control, eradication in regions outside Europe

  Bluetongue-free countries outside Europe aim to maintain their status through controlled importation of animals and germplasm from endemic countries, combined with vaccination strategies. A scientific report from EFSA concluded that, even when vaccination is applied to up to 95% of susceptible animals for a period of three years, bluetongue cannot be fully eradicated and may re-emerge. Only after at least five years of sustained vaccination does the level of infection approach near-eradication thresholds. Surveillance and vaccination can substantially reduce severe clinical losses; however, complete prevention and eradication remain unrealistic due to the circulation of multiple serotypes, the presence of wildlife reservoirs, and the vector-borne nature of the virus

• Costs of above measures

  Detailed studies on the costs of the above measures are not available for all scenarios. However, studies on evaluation of costs for BTV-8 epidemics in 2006–2009 estimates the costs as very high.

• Disease information from the WOAH

• Disease notifiable to the WOAH

  Yes.

• WOAH disease card available

  Yes.

  https://www.woah.org/en/document/bluetongue/

• WOAH Terrestrial Animal Health Code

  Terrestrial Animal Health Code, section 8 Multiple species, chapter 8.3 Infection with Bluetongue Virus

• WOAH Terrestrial Manual

  Terrestrial manual chapter 3.1.3. Bluetongue (Infection with Bluetongue virus)

• Socio-economic impact

• Zoonosis: impact on affected individuals and/or aggregated DALY figures

  None.

• Zoonosis: cost of treatment and control of the disease in humans

  None.

• Direct impact (a) on production

  Bluetongue (BT) can affect the livestock sector through multiple direct cost components, including mortality of valuable animals, veterinary costs, production losses (e.g. reduced milk yield), abortions and premature births Several studies have assessed the direct economic losses associated with BTV infection, particularly in relation to the major northern European outbreaks caused by BTV-8 between 2006 and 2008 and, more recently, by BTV-3 in North-western Europe during 2023–2024. Estimates from the BTV-8 incursions indicate that direct costs ranged between approximately 30 and 160 million euros, depending on the country and the year considered. The BTV-3 epidemic that occurred in the Netherlands in 2023 had a marked impact on cattle health across different production systems, including dairy herds, suckler cow operations, beef cattle farms and small-scale holdings. The outbreak was associated with a significant increase in abortions, premature births and mortality, highlighting the substantial direct production losses linked to BTV-3 infection in cattle. In small ruminants, particularly sheep, the epidemic resulted in a pronounced increase in mortality. In parallel, the rapid spread of BTV-3 across Belgium in 2024 was also associated with direct production losses affecting the livestock industry, although comprehensive quantitative estimates of the overall economic impact are still lacking.

  GAPS

  Lack of assessments of direct and indirect economic losses caused by BTV-3 and other BTV serotypes, including comprehensive cost–benefit evaluations of vaccination programmes.

• Direct impact (b) cost of private and public control measures

  Private costs include expenses borne directly by farmers and livestock operators, such as the cost of vaccination (when not subsidised) and losses related to movement restrictions. Public costs include laboratory testing of animals, epidemiological and entomological surveillance activities, vaccination campaigns when funded or reimbursed by governments and compensation provided to affected farmers.

  GAPS

  There is a lack of accurate and comprehensive estimations of the costs of control measures associated with the recent major outbreaks of bluetongue. This limits the ability to assess which interventions are cost-effective.

• Indirect impact

  Indirect losses include both additional costs and foregone revenues, such as expenses related to vaccination and, most importantly, losses resulting from trade restrictions that limit access to higher-value domestic and international markets. These indirect components often represent the largest share of the overall economic burden associated with bluetongue outbreaks. For example, the overall financial impact of the BTV-8 outbreak in 2007 was estimated at approximately US$ 1.4 billion in France and US$ 85 million in the Netherlands. In both countries, the majority of these losses were largely attributable to the trade restrictions imposed during the outbreak period, rather than to direct production losses alone.

• Trade implications

• Impact on international trade/exports from the EU

  Preventing the spread of disease through international trade is a primary objective of disease control tools. This is accomplished by establishing international standards that facilitate trade while minimising the risk of introducing diseases such as BT. In the last years, with the entry into force of Animal health law in EU, restriction on animal movements have been loosened, and costs related to these restrictions are much lower.

• Impact on EU intra-community trade

  Each Member State must establish and maintain an up-to-date list of its territory or zones with BT-free status, and must amend those lists within two working days, if the disease-free status of the territory or zones changes. Movements within the EU of live animals are regulated by Commission Delegated Regulation (EU) 2020/688. To avoid economic losses due to movement ban, the rules allow for certain derogations whereby the Member State of destination accepts animals in compliance with certain animal health conditions.

• Impact on national trade

  Not as strong as before. National rules usually allow for free animal movements if the territory is infected with whatever BTV serotype. No restrictions zones exist anymore.

• Links to climate

  Seasonal cycle linked to climate

  In many parts of the world, infection has a seasonal occurrence Climate, particularly ambient temperature and humidity, has an impact on the Culicoides life cycle and survival of the vector. It may also impact on the development of BTV in the vector.

• Distribution of disease or vector linked to climate

  For the typical BTV serotypes, presence and abundance of vectors are associated with climate and environmental conditions and, as a consequence, occurrence of disease is also linked to the vector. Warmer seasons may increase vectorial capacity.

  GAP

  Modelling the potential effects of climate change on the distribution of Culicoides vectors and BTV into the future.

• Outbreaks linked to extreme weather

  The specific role of extreme weather events, such as heatwaves, heavy rainfall, or droughts, in triggering outbreaks has not been systematically investigated.

• Sensitivity of disease or vectors to the effects of global climate change (climate/environment/land use)

  Predicted climate changes, including rising temperatures, could further expand the geographical range of Culicoides vectors, increasing the risk of disease emergence in previously unaffected areas. A northward spread of BT in Europe has already been observed over past years.

• Main perceived obstacles for effective prevention and control

  Effective prevention and control of bluetongue are challenged by several biological, ecological and technical factors. A major constraint is the high viral diversity and variability, with multiple BTV serotypes sometimes circulating simultaneously within the same regions. This diversity complicates diagnostics, surveillance and the implementation of vaccination campaigns, as available vaccines are serotype-specific. In addition, no vaccines are currently available against all serotypes, including newly emerged serotypes such as BTV-5 and BTV-12 recently detected in Europe. Moreover, effective large-scale vector control is extremely challenging and often impractical. Finally, important uncertainties remain regarding key aspects of BTV biology, including virus persistence and overwintering.

  GAPS

  Further understanding of the diversity and global distribution of different virus strains/serotypes / topotypes. Development of multi-serotype vaccines is paramount for effective disease control and preventive measures.

• Main perceived facilitators for effective prevention and control

  A strong veterinary and laboratory infrastructure is fundamental, as the availability of well-equipped laboratories and trained personnel allows for rapid and accurate diagnosis, timely reporting, and efficient outbreak response. Reliable diagnostic tools, including ELISA and PCR, enhance early detection of infections. The correct application of these tests is facilitated by trained laboratory staff, efficient systems for sample collection, transport and reporting. Vaccination is one of the cornerstone strategies for bluetongue control. The presence of safe, efficacious, and serotype-specific vaccines, combined with well-organized vaccination campaigns achieving high coverage in susceptible ruminants, significantly reduces disease incidence. At the policy level, clear national or regional control plans, regulations on animal movement and dedicated funding for surveillance, research, and emergency response are necessary for implementing those measures effectively. Finally, international collaboration, particularly with endemic countries bordering the Mediterranean Sea through a coordinated surveillance network, strengthens the overall capacity for bluetongue prevention and control. Such collaboration enables the identification of high-risk areas and the prioritization of control measures based on the exotic serotypes circulating in countries neighbouring Europe. This approach supports the development of a proactive diagnostic capacity, allowing for timely detection and response to emerging threats.

Main critical gaps

• -Despite significant advances in bluetongue virus biology knowledge and surveillance, diagnostics and control, several critical research gaps remain that limit the effectiveness of disease control tools.

  -development and validation of DIVA (Differentiating Infected from Vaccinated Animals) tests

  -development and validation of rapid, sensitive and specific pen-side diagnostic tests that can be used directly in the field to support early detection, particularly in remote or resource-limited settings

  -International collaboration and sustained monitoring in endemic countries remain insufficient. Strengthening long-term surveillance, data sharing and research partnerships in endemic regions is essential fro disease preparedness.

  -The development of multi-serotype vaccines represents another major research priority, given that multiple serotypes circulate in some regions.

  -from a diagnostic perspective, there is a need for serotype-specific ELISA assays to complement molecular tools, particularly for surveillance and post-vaccination monitoring.

  -improve the understanding of vector ecology and dynamics, including the expansion of Culicoides species driven by climate change and extreme weather events. Improved knowledge of how temperature, humidity, rainfall and extreme climatic conditions influence vector distribution, abundance and competence is critical for predictive risk modelling

Conclusion

• Bluetongue (BT) remains a major challenge for animal health systems due to the high genetic diversity of bluetongue virus (BTV), the co-circulation of multiple serotypes and the growing influence of climate change on transmission dynamics and virus expansion to previously free areas.

  Despite significant progress in diagnostics, surveillance and vaccination, the disease continues to cause substantial economic losses and trade disruptions.

  Vaccination is the cornerstone of BT control and has proven highly effective in limiting clinical disease during past epidemics. However, current vaccines are largely serotype-specific, lack DIVA capability and are often developed reactively in response to outbreaks. The recent emergence of new serotypes in Europe highlights the need for more proactive strategies, including multivalent vaccines posibly based on next-genaration vaccine platforsms, such as subunit vaccines, vectored vaccines and saRNA and mRA vacciens.

  Diagnostic tools for BT are generally robust, but require continuous updating to remain effective against emerging and reassortant strains. The absence of commercial DIVA diagnostics and the limited availability of rapid, field-deployable tests represent important gaps, particularly in resource-limited settings.

  Key uncertainties persist regarding BTV overwintering and long-distance spread of the virus through and the role of wildlife.

  Climate change is expected to further increase the risk of emergence and re-emergence in previously unaffected regions.

  Future control efforts should prioritise strengthened international collaboration, enhanced genomic surveillance, improved understanding of protective immunity and the development of innovative vaccines and diagnostics. Although eradication is unrealistic, a coordinated, science-based and anticipatory approach can substantially reduce the impact of bluetongue and improve preparedness for future incursions.

Sources of information

• Expert group composition

  -Alessio Lorusso (Leader) – WOAH and Italian Reference Laboratory for Bluetongue, c/o IZS dell’Abruzzo e del Molise “G. Caporale”, Teramo, Italy

  -Massimo Spedicato – WOAH and Italian Reference Laboratory for Bluetongue, c/o IZS dell’Abruzzo e del Molise “G. Caporale”, Teramo, Italy

  -Andrea Palombieri – WOAH and Italian Reference Laboratory for Bluetongue, c/o IZS dell’Abruzzo e del Molise “G. Caporale”, Teramo, Italy

  -Daria Di Sabatino – WOAH and Italian Reference Laboratory for Bluetongue, c/o IZS dell’Abruzzo e del Molise “G. Caporale”, Teramo, Italy

  -Melle Holwerda – Virology and molecular biology, c/o Wageningen Bioveterinary Research (WBVR), Lelystad, The Netherlands.

  -Damien Vitour - French Reference Laboratory for Bluetongue, ANSES/INRAE/ENVA-UPEC, UMR 1161 Virology, Laboratoire de santé animale, Maisons-Alfort, France.

  -Emmanuel Breard - French Reference Laboratory for Bluetongue, ANSES/INRAE/ENVA-UPEC, UMR 1161 Virology, Laboratoire de santé animale, Maisons-Alfort, France.

  -Pascal Hudelet - Boehringer Ingelheim Animal Health, Lyon, France

• Reviewed by

  Project Management Board.

• Date of submission by expert group

  January 2026

• References

  Recommended Citation:

  “Lorusso A.,Spedicato M.,Palombieri A.,Sabatino Da D., Holwerda M., Vitour D., Breard E., Hudelet P., 2026. DISCONTOOLS chapter on Blue Tongue Virus https://discontools.eu/database/38-bluetongue.html.”

  References:

  EFSA AHAW Panel (EFSA Panel on Animal Health and Welfare), More S, Bicout D, Bøtner A, Butterworth A, Depner K, Edwards S, Garin-Bastuji B, Good M, Gort azar Schmidt C, Michel V, Miranda MA, Nielsen SS, Raj M, Sihvonen L, Spoolder H, Stegeman JA, Thulke H-H, Velarde A, Willeberg P, Winckler C, Mertens P, Savini G, Zientara S, Broglia A, Baldinelli F, Gogin A, Kohnle L and Calistri P, 2017. Scientific Opinion on the assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bluetongue. EFSA Journal 2017;15(8):4957, 74 pp. https://doi.org/10.2903/j.efsa.2017.4957

  Hanekom J, Ebersohn K, Penzhorn L, Quan M, Leisewitz A, Guthrie A, Fosgate GT. Bluetongue Virus Infection in Farm Dogs Exposed to an Infected Sheep Flock in South Africa. Transbound Emerg Dis. 2024 Jul 29;2024:2446398. doi: 10.1155/2024/2446398.

  Ul-Rahman A, Shabbir MZ, Wensman JJ. Bluetongue virus in carnivores: expanding the host range and implications for disease ecology. Vet Q. 2025 Dec;45(1):2588740. doi: 10.1080/01652176.2025.2588740.

  Caballero-Gómez J, Sánchez-Sánchez M, Lorca-Oró C, de Mera IGF, Zorrilla I, López G, Rosell R, Grande-Gómez R, Montoya-Oliver JI, Salcedo J, Paniagua J, Cano-Gómez C, Gonzálvez M, García-Bocanegra I. Bluetongue Virus in the Iberian Lynx (Lynx pardinus), 2010-2022. Emerg Infect Dis. 2024 Oct;30(10):2169-2173. doi: 10.3201/eid3010.240235.

  Capper JL. The impact of controlling diseases of significant global importance on greenhouse gas emissions from livestock production. One Health Outlook. 2023 Dec 8;5(1):17. doi: 10.1186/s42522-023-00089-y.

  Kyriazakis I, Arndt C, Aubry A, Charlier J, Ezenwa VO, Godber OF, Krogh M, Mostert PF, Orsel K, Robinson MW, Ryan FS, Skuce PJ, Takahashi T, van Middelaar CE, Vigors S, Morgan ER. Improve animal health to reduce livestock emissions: quantifying an open goal. Proc Biol Sci. 2024 Aug; 291(2027):20240675. doi: 10.1098/rspb.2024.0675.

  Puggioni G, Pintus D, Meloni G, Scivoli R, Rocchigiani AM, Manunta D, Savini G, Oggiano A, Ligios C. Persistence of Bluetongue virus serotype 1 virulence in sheep blood refrigerated for 10 years. Vet Ital. 2018 Dec 31;54(4):349-353. doi: 10.12834/VetIt.1344.7401.3.

  https://www.woah.org/en/article/bluetongue-in-europe-how-climate-change-is-shifting-disease-patterns/?utm_source=chatgpt.com

  Hudson AR, McGregor BL, Shults P, England M, Silbernagel C, Mayo C, Carpenter M, Sherman TJ, Cohnstaedt LW. Culicoides-borne Orbivirus epidemiology in a changing climate. J Med Entomol. 2023 Nov 14;60(6):1221-1229. doi: 10.1093/jme/tjad098.

  Dijkstra E, Santman-Berends IMGA, Stegeman A, van den Brink KMJA, van Schaik G, van den Brom R. Evaluating the effect of vaccination on the impact of BTV-3 in Dutch sheep flocks in 2024. Vet Microbiol. 2025 Oct; 309:110652. doi: 10.1016/j.vetmic.2025.110652.

  Van Leeuw V, De Leeuw I, Degives N, Depoorter P, Dewulf J, Hanon JB, Hooyberghs J, Linden A, Praet L, Raemaekers M, Saegerman C, Simons X, Sohier C, Steurbaut N, Sury A, Thiry E, Zientara S, Mauroy A, De Regge N. Impact of BTV-3 Circulation in Belgium in 2024 and Current Knowledge Gaps Hindering an Evidence-Based Control Program. Viruses. 2025 Apr 3;17(4):521. doi: 10.3390/v17040521.

  van den Brink KMJA, Brouwer-Middelesch H, van Schaik G, Lam TJGM, Stegeman JA, van den Brom R, Spierenburg MAH, Santman-Berends IMGA. The impact of bluetongue serotype 3 on cattle mortality, abortions and premature births in the Netherlands in the first year of the epidemic. Prev Vet Med. 2025 Jun; 239:106493. doi: 10.1016/j.prevetmed.2025.106493.

  Santman-Berends IMGA, van den Brink KMJA, Dijkstra E, van Schaik G, Spierenburg MAH, van den Brom R. The impact of the bluetongue serotype 3 outbreak on sheep and goat mortality in the Netherlands in 2023. Prev Vet Med. 2024 Oct; 231:106289. doi: 10.1016/j.prevetmed.2024.106289.