1) Pathogenesis and persistence in the host

1. Assess virulence of BTV strains within common European sheep breeds
2. Investigate cellular as well as humoral immune responses within the host
3. Investigate the molecular and genetic basis of virulence of BTV
4. Investigate the duration of the infective period in sheep/cattle and the period over which vector Culicoides can be infected
5. Investigate the possibility of transovarial transmission of BTV in its vectors
6. Investigate potential for covert persistence mechanisms in the ruminant host.

2) Vector competence and vector-virus interactions

1. Quantify competence levels of populations of potential BTV vector species particularly within novel vector groups in Europe.
2. Determine whether and how the competence of these vectors varies with climate
3. Investigate the molecular and genetic basis of susceptibility (infection and transmission barriers) in Culicoides vectors
4. Identification of the molecules and/or receptor sites involved in virus-insect host cell interactions
5. Investigate whether particular strains of BTV overlap with particular vector species or genotypes. Determine the role of polymorphism in both viruses and vectors to help predict the outcome of particular strain-vector interactions

3) Epidemiology and modelling

Whilst some participants felt that the seasonality of vector activity and vector distributions were adequately known - others felt that more detailed investigation of these patterns and the processes underlying them would answer a range of important epidemiological questions and lead to more accurate risk maps that could be utilised to target control measures.

1. Quantify the distribution limits of potential European Culicoides vectors. Further define what constitutes suitable habitat for vectors within these limits – particularly for C. imicola in the northern Mediterranean Basin.
2. What are the climatic and other factors that prevent the spread of BTV throughout the distribution of its competent vectors? In particular, what are the thermal requirements (in day degrees) for transmission of BTV?
3. Quantify the number of vectors (abundance levels) required for BTV transmission and the environmental factors that govern vector numbers and seasonality.
4. Model the basic reproductive rate (R0) across Europe to determine whether, when and where BTV is likely to persist and become endemic.
5. Molecular characterisation (sequencing) of all vaccine viruses, and of field strains of BTV isolated in the region and elsewhere.
6. Addition to and sharing of existing BTV sequence databases to enable more detailed inferences to be made about the origins of incursions and the relatedness of virus strains
7. Dissemination of BTV into and around the fringes of Europe via ruminant livestock movements. Monitor such movements to gain an understanding of risk levels and to identify potential portals and times of virus entry into Europe.
8. Movement of BTV into and around Europe: Characterization of winds involved in long distance Culicoides transport
9. Investigate the role of wild ruminant hosts in BT epidemiology
10. Identify those vector-borne pathogens most likely to become a major risk to Europe over the next 10 years.

4) Surveillance and diagnostics

Participants emphasised the need for Europe-wide dissemination of information that is collected on BTV circulation within countries. It was felt that existing surveillance methods should be standardised (e.g. timing and frequency of serum-sampling, comparison of trap efficiency between the different light traps in use or use of a single light trap type only).

1. Initiation of a Europe-wide, coordinated ruminant sentinel surveillance system for monitoring of BTV infection/occurrence
2. Inclusion of neighbouring areas in sentinel system (North Africa, Turkey and the Middle East) to act as an early warning system
3. Better definition of sentinel and vector surveillance work required to assess ‘disease-free status’ of a country
4. Improved information technology for storage, communication and sharing of vector and sentinel surveillance data
5. Development of cost-effective molecular methods for vector species identification particularly for the novel vector groups in Europe
6. Development of tests to allow differentiation between infected and vaccinated animals, for live virus vaccines and inactivated/sub unit vaccines
7. Optimise techniques for detection of viruses from insect samples and for detection of small amounts of infectious BTV in the vertebrate hosts

5) Vector control

The paucity of experimental work on vector control methods for Culicoides was highlighted as well as the considerable potential for the development of chemical products in partnership with industry. Pour-ons for ruminants as well as repellents were mentioned specifically. However, before the effect of control methods on vector populations can be accurately ascertained there is a need to acquire basic entomological data on vector breeding site characterization and the effect of farm husbandry practices on vector numbers.

1. Characterize the breeding sites of important vector species in Europe
2. Determine the factors affecting vector numbers at the farm-level
3. Test and compare vector control strategies and methodologies
4. Investigate commercial development of most effective products in partnership with industry

6) Vaccination

Live-virus vaccines have been used successfully to control BT disease in certain areas for many years though concerns about the production of clinical signs in some sheep breeds, the development of viraemia in vaccinates and the high potential for onward transmission by Culicoides in the field, possibly leading to re-assortment with field strains were highlighted. New whole virus inactivated vaccines are currently being developed that do not suffer from such drawbacks and sub unit vaccines are likely to be the next stage. Further development and refinement of these new vaccines was considered essential as was the development of delivery systems designed to enhance and extend protection. The benefits accrued by the development of such technologies could extend to human as well as animal diseases. The early involvement of industrial partners in these studies was considered of high importance to ensure that new products become commercially available as rapidly as possible. The issue of the complex regulatory requirements required to get products to the market in Europe was compared unfavourably to other regions of the globe on several occasions.

1. Investigate responses of common European sheep breeds, cattle and goats to live BTV vaccination and to vaccination with the new inactivated or sub unit vaccines
2. Confirm efficacy and duration of protection of new inactivated vaccines.
3. Devise, test and apply novel delivery systems designed to enhance vaccine performance
4. Develop second generation inactivated vaccines based upon “virus like particles”, proteins or other viral components
5. Develop group-specific BTV vaccines, possibly based upon “core like particles” or serogroup proteins.
6. Determine the level of immune response required for protection
7. Develop a framework to speed up authorisation of vaccines that incorporate new strains of virus as the need arises

Conclusion

Advances have been made in the knowledge of BT disease and in the tools for its prevention and control. However, it is a complex disease which is expanding in the EU and major research efforts need to be pursued. As a transboundary disease bluetongue needs to be tackled at international level also with regard to research. The research needs identified will be taken into consideration when developing EU research programmes and the Strategic Research Agenda of the European Technology Platform for Global Animal Health.