Lamb virus is here, warns Chief Vet He said that a "key question" now was whether the virus had survived the winter in the midge population. How might it overwinter? We don't yet know the biology, but surviving small pockets of midges is one theory. An outbreak of the similar midge-borne virus bluetongue in 2007 was resisted with a buffer zone of farms in southern England, within which animals were vaccinated and livestock movements restricted. But if Schmallenberg virus is now being passed from generation to generation of midges in Britain, it may well become impossible to contain. Mr Gibbens said scientists were also investigating other possible ways in which the virus could have survived the winter. An ability for infectious virus to remain in previously-infected animals is another theory, although the early indications are that they do seem to clear the virus. Then there is the possibility that an animal infected at the right time in pregnancy gives birth to a calf or lamb that still has infectious virus later in the year when midges are active - could that kick it off again in a coming year? We don't know the answer to that yet. More than a thousand farms in Europe have reported cases of Schmallenberg virus, which is named after the town in Germany where it was first seen last summer, and which also affects cattle and goats. The full scale of infection may be hidden by farmers not reporting the virus when it affects their livestock, Mr Gibbens said. It's hard for us to know. We need to work with the National Farmers Union to try to get to grips with under reporting. You can't tell at this stage what level of under reporting there is. Matthew Baylis, a professor of veterinary epidemiology at the University of Liverpool, said the cases reported so far were "likely to be the tip of the iceberg." Detection currently relies on finding evidence of the actual virus in animals, which is difficult as viral infection is usually transitory. It would be better to test for antibodies which linger in the blood for months, he said, but no such test yet exists. When such a test is successfully developed, it is likely that much larger numbers of farms in Great Britain will be found to have been infected by the virus. Frank Langrish, a sheep farmer from Rye in East Sussex and a leading member of the NFU said he believed that fewer than one in ten cases of infection were being reported. "Of the 30 or so local farmers I have spoken to, only two have not had incidents related to Schmallenberg," he said. That would mean there were nearly a thousand farms affected in this country. Mr Langrish is a member of the NFU's livestock board in the south east of England and a former chairman of the British Wool Marketing Board. He said the reasons why farmers did not send the lambs for testing included the stigma of having the virus and the fact that research laboratories were closed at weekends. "Others are now anticipating the disease, so that even if they get large numbers they just say 'Oh well, that's Schmallenberg" and don't bother to have it tested. When you're busy with lambing, you don't worry about the dead ones, you get on with looking after the live ones.