Research reveals how midges spread disease

Scientists at Oxford University this week published evidence that the midges that spread bluetongue across Europe in 2006 were not in fact passengers on the wind as previously thought but rather were capable of flying into headwinds to spread the disease.

The outbreak of bluetongue in the UK in 2007 resulted in widespread animal movement restrictions which resulted in millions of pounds of lost revenue for livestock farmers and massive disruption. In Belgium it killed thousands of sheep and meant that agricultural shows across the country, including several in Yorkshire, had to cancel their livestock classes.

A vaccination programme to combat the disease cost millions of pounds to the taxpayer and the country was only declared free of the disease last year.

A team led by Oxford University scientists analysing the outbreak has shown that active movements of the midges were responsible for around 40 per cent of the spread of the epidemic.

“For the first time we can say that midges, under their own power, travel upwind as well as downwind during this kind of epidemic,” said Dr Luigi Sedda of Oxford University’s Department of Zoology, who led the research with Professor David Rogers.

“This has very important implications for the control of future epidemics as previously efforts had been targeted at preventing downwind infection.”

Bluetongue is a non-contagious virus that causes symptoms such as drooling, and swelling of the neck, head and tongue in sheep, cattle, goats, deer and other ruminants. It is transmitted between animals by the Culicoides midge.

The analysis was restricted to Northern Europe (France, Belgium, Netherlands, Germany, and Luxembourg). Nearly 40 per cent of the midge’s movements during the outbreak were attributed to their own activity with downwind and random movements, or combinations of upwind, downwind and random movements, accounting for the remainder of the infections.

Dr Sedda said: “Our model can explain 94 per cent of the over 2,000 farm outbreaks of bluetongue in Northern Europe in 2006. Whilst some infected farms were the source of infections for up to 15 other farms, 70 per cent of all the infected farms were transmission ‘dead ends’ – that is they did not infect other farms.

“These sorts of statistics could help to inform future control policies for bluetongue and other diseases that are spread in a similar way.”