Bluetongue Serotype 8 Epidemic Bulletin
Bluetongue Serotype 8 Epidemic Bulletin by EFSA Epidemiology Working Group
23/10/2006
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23/10/2006
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Bluetongue epidemiological evaluation
The mandate for the epidemiological analysis was received by EFSA on the 5th October 2006. It is handled by the Assessment Methodology Unit in the SCA department of EFSA.
The mandate consists of two components. The first pertains to a regular update on the evolution of the disease, the second to a global epidemiological analysis.
The proposal was presented to the Member States’ Chief Veterinary Officers (CVOs) and the European Commission on 26th October meeting, which was organized by the Commission and the Finnish presidency. The results obtained until 31 January were presented to the CVOs at a Commission meeting on bluetongue on the 7th February in Brussels. A summary of these slides are available at the link below. The work is targeted for completion by 31 March 2007.
A subgroup has met on a weekly basis to work first on the regular update and then also on the global epidemiological analysis. The 1st full working group meeting took place on the 6th October. The working group met again on the 15th December in Paris to review progress and further proposed actions. The bluetongue working group met on the 6th February in Parma to review the results obtained up until 31 January.
Regular update
- The purpose of this bulletin was to characterise the epidemic that started in August 2006 using clinical outbreak data. The updating took place through weekly postings on the EFSA website.
- Most newly reported cases in January are likely to be herds where the animals became infected several weeks ago. For an evaluation of the clinical outbreaks it is therefore recommended to consider the data until the end of December only.
- This task was completed successfully and the weekly reporting was therefore discontinued.
Global epidemiological analysis
The conduct of a global epidemiological analysis requires a willingness to share data between the affected member states, a need to collect these data, and to standardize them so as to be able to incorporate them in a single analysis dataset. This activity has required quite an effort and is in many ways novel. The timeline for completion of the data acquisition and exchange is 15 January 2007.
In order to make sure financial support was adequate, EFSA launched a tender with four national research institutes (from Belgium, France, Germany, and the Netherlands). These were completed successfully by the end of December.
A first set of results up until 31 January were delivered and presented. As stated, the final reports are due 31 March. The initial findings reported by the EFSA bluetongue working group are that:
1. Statistical modeling showed that the initial infection occurred in area close to Maastricht. Difficulties in the initial diagnosis were due to the fact that the disease was thusfar not known (exotic) in the area. The exact cause of the introduction is not known.
2. The BTV8 virus was present in vectors (Culicoides species) which are endemic to northwestern Europe. The prevailing high temperatures in the summer of 2006 resulted in high numbers of various Culicoides species. Thus, the warm(ing) climatic conditions may favour the establishment of these viruses after they have been adventitiously introduced in a new part of Europe.
3. The number of new bluetongue cases over time was equally influenced by changes in temperatures. This resulted in an initial peak and then a second peak of new cases which were separated by a cooler period.
4. Besides temperature, the number of observed bluetongue cases was also related to other environmental factors such as altitude and animal density.
5. Local spread was modeled and found to occur at a rate of about 16 km per week. In addition, it was demonstrated that, beside animal movement – which is subject to restrictions, wind may affect spread over long distances.
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