The Schmallenberg virus was discovered in Germany in autumn 2011. It was discovered that the disease had arrived in England in December 2011. The disease, which affects goats, deer, sheep and cattle, causes flu-like symptoms in infected animals and can lead to birth defects if animals contract the disease at a key stage of pregnancy.

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Once infected, animals develop immunity to Schmallenberg, which led experts to express the hope that this disease's impact would be short-lived. A vaccine against Schmallenberg virus was also developed earlier this year.  

Initially, disease experts speculated that the disease likely arrived on UK shores, having been carried by midges blown over the English Channel. Research released on Thursday (28^th October) appears to confirm their hypothesis, suggesting that midges from French and Belgian farms were responsible for the spread of the virus into England in early summer 2011.

Researchers from the University of Oxford showed that, statistically, the most likely source of early infections on the English coast are farms on the coast of France and Belgium. They also showed that the spread of SBV is highly reliant upon wind direction, and that the disease spreads more widely that the pattern of birth defects would suggest.

The study offered a detailed insight into the spread of SBV, which is related to other devastating livestock diseases such as Bluetongue. In addition to suggesting that midges from "at least ten farms in France and Belgium" brought Schmallenberg to England, the research showed that around half of infected farms across Europe are 'dead-ends' that do not go on to spread the disease further.

The researchers behind the study said they hope their findings will be of use to policy makers and farmers looking to understand and prevent the spread of viruses such as SBV.

Dr Luigi Sedda of Oxford University's Department of Zoology, elaborated on the difficulty of controlling diseases such as SBV, which caused widespread panic upon its discovery, "We found that most birth defects in sheep were caused by Schmallenberg infections approximately five to six weeks after conception. The first infected sheep was reported on 14 December 2011, so that was probably caused by an infectious midge bite around the 11 August. The lag time between infection and detection makes it difficult to control the virus, particularly as it spreads so quickly."

It is believed that over 8,000 farms across Europe have been affected by Schmallenberg virus since 2011, but, as the disease remains non-notifiable in the majority of countries where it has been discovered, scientists have had difficulty mapping its progress and developing strategies to tackle it.

Professor David Rogers, also of the Department of Zoology, said, "One of the problems with diseases like Schmallenberg is the lack of a national strategy for reporting or control. It is impossible to get up-to-date infection data with farm-by-farm detail. Farmers are understandably cautious about declaring infections, but better reporting across the country could benefit the whole industry. We could potentially predict the probability that a farm has been infected (and hence contains immune animals), allowing farmers to make more informed decisions about whether or not to spend money on vaccinations."

He added, "In Germany and the Netherlands Schmallenberg is a [notifiable disease], but in the UK… we don't record it or routinely test for it. 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."