THE COMING months are "odds on for a barbecue summer", according to the Met Office's long-range forecast issued at the end of April. It's likely that summer temperatures across the UK will be warmer than average and rainfall near or below average.
The forecast infers that there may be several days when the temperature reaches 30°C or higher - something that happened only once during 2008.
This raises the stakes for bluetongue in the UK this year, as warm weather is a major risk factor.
The hotter it is, the faster bluetongue virus grows in Culicoides biting midges, which are the transmitters (vectors) of bluetongue virus. It is then only a matter of days before an infected midge is able to transmit the virus to more livestock when it sucks blood from them.
The Met Office's forecast adds impetus to the Joint campaign Against Bluetongue (JAB) drive for 2009, whose main message is "don't hesitate, vaccinate".
We know that the adult midges are rapidly increasing in numbers and that they are now biting livestock. We have analysed temperatures at St. Brieuc, on the north coast of France, as it is midges from the near Continent that will once again pose a threat to Britain.
The graph below shows that temperatures suitable for adult midge activity were reached on most days during March and April of this year, and temperatures suitable for virus growth (above 12°C) also occurred.
The Institute for Animal Health is the home of the Culicoides Reference Laboratory. We have established 16 Culicoides traps on farms across the UK, which are set in the evening. The following morning the caught insects are sent to our Pirbright laboratory for microscope analysis. One objective is to count how many of the Culicoides midges are 'parous': have taken a blood meal, developed an egg hatch, laid it, and are now looking for their second blood meal.
When five or more such midges are caught in one trap on a single night, this signals the end of the vector-free period.
On 23 April, the IAH reported the end of the vector-free season in the UK, having seen 12 parous midges in a sample from north Devon. So, Britain has entered the bluetongue at-risk season.
Although two new serotypes of bluetongue virus (BTV-6 and BTV-11) were detected in neighbouring countries last year, it is not clear if these pose a significant threat to livestock in the UK. However it is clear that serotypes 1 and 8 are potent threats.
As BTV-8 is more widespread and entrenched in northern Europe than BTV-1, type 8 is still considered to be the biggest threat to the UK. Hence JAB's exhortation to take active steps; vaccinate with BTV-8 vaccine.
Although France has had a vaccination campaign during the winter, applying both BTV-1 and BTV-8 vaccines, it would be dangerous for British livestock farmers to rely on that measure alone to remove the risk in the UK. Apart from any other consideration, we should remember that the first midges to bring BTV to us, in 2007, came from Belgium, not France.
Midges are not the only source of introduction of BTV into the UK; imported infected livestock are another.
This did happen in Britain last year. Fortunately there was no successful onward transmission of the virus. Thanks for that are due to those British farmers who did vaccinate against BTV-8.
In France, where the disease spread faster than the application of vaccine, over 24,000 farms suffered from the disease. We have been warned.
Article written by Dave Cavanagh, Institute for Animal Health, with John Gloster and Laura Burgin.
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