EUROPE – Schmallenberg virus (SBV) spread to the United Kingdom from farms on the French and Belgian coast, a paper published in Scientific Reports has shown.
Researchers at Oxford University have suggested that winds spread the disease vector, the Culicoides midge, across the channel from ten farms.
However, the report also found half of Europe’s infected farms did not spread the virus, acting as ‘dead ends’.
"The first infected sheep was reported on 14 December 2011, so that was probably caused by an infectious midge bite around the 11 August," said Dr Luigi Sedda of Oxford University's Department of Zoology, lead author of the paper.
Using probabilistic wind pattern modelling, the study demonstrated the coverage of the virus, confirming its dependence on wind direction.
Wind mapping was used in 2011 by the Meteorological Office to predict spread from the continent to the UK, explained senior report author, Professor David Rogers of Oxford University’s Department of Zoology.
“The Met office was mapping wind fields for Blue tongue virus spread and did the same when SBV cropped up in Europe,” said Professor Rogers.
He emphasised the inherent difficulty in monitoring a disease without notifiable disease status and commented that the price of serological testing may have dissuaded government departments and producers from fully monitoring the disease.
Dr Sedda said: "The lag time between infection and detection makes it difficult to control the virus, particularly as it spreads so quickly."
"We found that most birth defects in sheep were caused by Schmallenberg infections approximately five to six weeks after conception."
Four out of five farms may not have susceptible pregnant animals when the midges arrive, explained Professor Rogers, stating that there could be 'stepping stones' in the path of the disease not seen.
Notifiable status in the UK would have been advisable, suggested Professor Rogers. This would have put UK farmers on a similar playing field to European producers, most of which had to notify.
Professor Rogers added: “On the European continent, government generally classed Schmallenberg as a notifiable disease, resulting in a higher percentage of reported cases.”
“However, where reporting is voluntary, which it initially was in the Netherlands, notifying was very patchy –some farmers reported and some didn’t.”
“Until Schmallenberg was made notifiable, the Netherlands was not really aware of the size of the problem it had.”
But he added, “Curiously, in Germany the disease was not officially notifiable for about the first six months. The German farmers however, were reporting voluntarily, at a much higher rate than Dutch farmers were.
“We are reasonably sure that German figures were quite accurate before it was made notifiable in Germany.”
"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."
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