Dec. 9, 2013, 5:43 p.m.
A virus that hit farms in the UK last year came from midges blown across the Channel from France and Belgium, scientists have confirmed.
The Schmallenberg virus, which emerged in the Netherlands and Germany in 2011, can lead to sheep and cattle having stillborn or deformed offspring.
The disease has affected more than 8,000 farms across Europe.
The findings, in Scientific Reports, could help farmers understand more about the control of livestock viruses.
Research by zoologists at Oxford University shows the disease was introduced from across the Channel by infected midges from at least 10 farms in France and Belgium.
Modelling data suggests Schmallenberg spreads more widely than previously thought, and is dependent on wind direction.
About half of infected farms across Europe did not go on to spread the disease further.
"We found that most birth defects in sheep were caused by Schmallenberg infections approximately five to six weeks after conception," said Dr Luigi Sedda.
"The lag time between infection and detection makes it difficult to control the virus, particularly as it spreads so quickly."
The findings could help farmers and policymakers understand more about the spread of viruses such as Schmallenberg and plan how best to control them, say the researchers.
The virus is not a notifiable disease in the UK, unlike in Germany and the Netherlands.
"One of the problems with diseases like Schmallenberg is the lack of a national strategy for reporting or control," said Prof David Rogers.
"Previous tests in Belgium have shown that the disease is far more widespread than the reported cases, as animals that are not at the critical stage of pregnancy may carry the disease unnoticed.
"There are probably many 'stepping stones' in the path of the disease that we don't see because four out of five farms may not have susceptible pregnant animals when the midges arrive."
A vaccine against Schmallenberg became available earlier this year, but it is not clear how many farmers have chosen to vaccinate.
The virus has infected more than 1,000 farms in England and Wales, and more than 30 in Scotland, according to the latest figures.