Study examines bluetongue spread

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How to be a midge catcher

Scientists are attempting to understand how bluetongue is spread by studying the movements and biting habits of the midge species that transmit the virus.

Researchers from the UK's Institute for Animal Health (IAH) say the findings can be used to advise farmers how and when to protect their livestock.

Since the first outbreak on a farm in the Netherlands in 2006, the virus has affected most parts of northern Europe.

In 2007, the farming region's direct losses are estimated at more than £95m.

The results are incorporated with meteorological data to create models showing what weather conditions are most likely to see the insects becoming active, and when farmers should take increased measures to protect their animals.

Net results

"We have to think to ourselves when are the midges going to be active and what can we do to put a barrier between our livestock and these midges," said lead researcher Simon Carpenter.

"We will use our models to advise on best practice for measures such as stabling, insecticide use and vaccination, to control the spread of the bluetongue virus."

The IAH team developed two methods to monitoring the movements and biting behaviour of Culicoides midges, which spread the virus.

Warmer weather is believed to have allowed infected midges to move north

The first involved using a large net on top of a 4x4 vehicle that is driven at a constant 20 mph (32km/h) over a known distance through grazing meadows. This allowed the scientists to calculate the number of midges per cubic metre of air.

The second method focused on the biting habitats of the midges.

The team lowered a muslin tent over a pen of sheep that had been exposed for 10 minutes. The researchers then entered the tent to collect the midges, which where analysed to establish which species were biting the sheep.

"The benefit of these techniques is that, until very recently, midge surveillance relied upon the use of light traps that sometimes did not represent what was happening on the animals very well," explained Dr Carpenter.

"Using these two techniques, we can more easily understand the relationship between weather conditions and both background midge activity and biting attacks."

Northward spread

He added that it also helped to predict the level of risk at different times of year when the data was combined with weather forecasts.

Bluetongue, which was first detected in the UK in September 2007, is spread by the midges when it bites an infected animal and ingests the virus, which is in the animal's blood. The virus then infects the midge, which can then transmit it to the next animal it bites.

Bluetongue can infect all ruminant animals, including, sheep, cattle, deer and goats.

Since bluetongue arrived in the UK, the government has set up protection and surveillance zones in an effort to monitor and control the spread of the disease.

Until the first recorded case in northern Europe, at a farm on the Dutch/German border in August 2006, the disease had been confined to the Mediterranean region.

However, it is believed that warmer temperatures have created the conditions for infected midges to move northwards.