'Midge maps' could help prevent bluetongue spread in UK

September 4, 2008

Ecologists have developed a new technique for genetically identifying species of biting midges that could help prevent the spread of bluetongue among livestock in the United Kingdom.

Bluetongue affects all ruminants, including sheep, cattle, deer and goats. It is closely related to deadly African Horse Sickness and is carried by the same midges. Bluetongue was first detected in the UK in 2007. There are fears that African horse sickness, which has already affected mainland Europe, may also soon appear on its shores.

Jane DeGabriel, of the University of Aberdeen, will today speak at the British Ecological Society's annual meeting at Imperial College, London, to explain how the technique will plug a huge gap in our understanding of how midges might spread bluetongue in the UK.

The disease can be spread by species of Culicoides biting midge present in the UK. European midges have been exposed to bluetongue and can spread the disease. Coupled with climate change, this means the disease poses a major threat to UK agriculture.

The species of midges present in the UK potentially differ in their ability to spread bluetongue, so predicting how the disease might spread depends on mapping the distribution of these species.

DeGabriel's new "bar-coding" system makes this possible for the first time.

According to DeGabriel: "The four species within the group Culicoides obsoletus that we are interested in cannot be distinguished visually.

"So we are using a genetic bar-coding approach to identify the midges to species level using molecular methods. We have developed a high-throughput genetic screening method to identify large sample sizes of midges to species level, both efficiently and cost-effectively."

During 2007 and 2008, DeGabriel and her colleagues collected one million midges from light traps set up on 37 farms throughout Scotland, from the English border in the south to as far north as Thurso.

Using the bar-coding technique they were then able to produce a detailed "midge map" of Scotland. This showed midge numbers and species varied both geographically and seasonally, reflecting differences in climate and habitat.

"This is the first large-scale study of the distribution and abundance of Scottish midge species. We found that all four species of midges were present in all areas of Scotland, but the relative numbers of each species differed between the trapping sites.

"We also found the mixture of species differed at individual sites at different times of the year. These differences between and within sites appear to be due to differences in climatic conditions and habitat. Our findings provide vital information for assessing the risk of bluetongue being transmitted in Scotland and the effects of climate change on the spread of this and other animal diseases," DeGabriel explains.

"Given the introduction of bluetongue into England and the persistence of favourable climatic conditions such as the recent milder winters, this research is extremely urgent and important.

"Our results will help scientists and policy makers develop risk mitigation and management strategies for bluetongue and other animal diseases," DeGabriel says.

Jane DeGabriel will present her full findings later today at the British Ecological Society's meeting.

Her research is being carried out under a Scottish Government grant to the University of Aberdeen, Advanced Pest Solutions Ltd and the Institute for Animal Health, Pirbright.