The number of farms affected by the Schmallenberg virus in the UK has risen to 83, according to the latest government figures.
Nine more farms in the south of England have confirmed the virus, which causes birth defects and miscarriages in livestock, the Animal Health and Veterinary Laboratories Agency (AHVLA) said.
In England, it has now been identified on the Isle of Wight and in Wiltshire, west Berkshire and Gloucestershire.
This is in addition to farms in Norfolk, Suffolk, Essex, Kent, East and West Sussex, Hertfordshire, Surrey, Hampshire and Cornwall, which have previously identified cases.
Five of the positive cases have been diagnosed in cattle, 78 in sheep, and none to date in other animals. The Food Standards Agency said it was “unlikely” that the disease is of any risk to humans.
The most number of cases have been reported in eastern counties, including 14 in Norfolk, 12 in Suffolk and 13 in Kent.
So far there have been no confirmed cases in Wales or Northern Ireland. But farmers in both countries have been put on alert because the disease is now being detected further west.
DEFRA said it was vitally important farmers continued to report any suspicious cases as soon as possible.
The Schmallenberg virus causes mild to moderate symptoms in adult cattle, including reduced milk yield, and stillbirth and birth deformities in sheep, cattle and goats.
Mortality rates of up to 25% have been recorded in newborn lambs.
Scientists believe the virus is spread by biting midges and it first appeared on the continent before crossing the Channel.
Germany, where the virus originated, has had the largest number of confirmed cases (668), followed by France (152), Belgium (144) and The Netherlands (108).
David Willison, who keeps sheep and Jersey cattle at Cinderbarrow Farm in Levens, near Kendal, Cumbria, told BBC Radio 4’s Farming Today programme of his concerns.
“The not knowing is the worst feeling of all,” he said. “Because you are trying to plan the management of your stock and the sale of your stock, and you’ve got this niggle in the back of your mind that something might be coming around the corner and it might take it all away from you.”
Malcolm Bennett, professor of veterinary pathology at Liverpool University, said: “The economic and social effects of the disease for farmers whose animals are infected are still to be seen.
“The main effect in sheep is on unborn lambs, so only now, as we enter the peak period for lambing, are we beginning to see the extent and severity of the disease.”
Alistair Mackintosh, livestock board chairman of the NFU, said the disease had the potential to be become catastrophic in the UK.
In 2007, farmers in the UK lost millions of sheep and goats to the bluetongue virus, which was also brought by midges, but has now been eradicated.
However, a vaccine for the Schmallenberg virus does not exist and scientists say it could take up to two years to develop.
Peter Mertens, head of vector-borne viral diseases from Surrey’s Institute for Animal Health in Pirbright, is researching the virus.
Prof Mertens told BBC Radio 5 Live on Monday (27 February) that he and his team had received samples of the virus and were about to begin testing it on insects.
“In the next couple of days we are planning to put the virus into insects from our colonies of culicoides, midges and mosquitoes and that should give us a much clearer picture of whether or not it infects the insects and whether or not they can transmit it.”
But he added that until a vaccine is found there was nothing that farmers could do to prevent the disease.
“To some extent the picture that’s emerging now is last year’s story,” said Prof Mertens.
“The adult sheep were infected probably late last summer while they were pregnant.
“The adult was probably a bit off colour for a few days – maybe a bit of diarrhoea and temperature, but then made what appears to have been a full recovery. In many cases, this may not even have been picked up.
“The virus crosses the placenta and causes damage to the developing fetus, such that the lamb or calf is deformed or even dead.”