Researchers at the Royal Veterinary College, in collaboration with colleagues at Pirbright, have confirmed that Schmallenberg virus is still circulating in the UK as the current midge season approaches its peak. Tests were carried out on around 150 cattle and over 1000 sheep belonging to the Royal Veterinary College, where MSc student Corin Jack is studying Schmallenberg epidemiology. The tests looking for antibodies to the Schmallenberg virus were done using a commercially available testing kit.
Professor Peter Mertens, who leads the Pirbright team, which receives strategic funding from the Biotechnology and Biological Sciences Research Council (BBSRC), said “Animals that had originally been negative for antibodies against the virus became positive between March and June 2012, indicating that the virus has survived the winter and is circulating here during the current midge season. We had hoped that it might simply burn itself out and fail to make reappearance this year but this has not been the case.”
“Thankfully there are unlikely to have been many animals at the critical stage of pregnancy during the midge season so far but as the year goes on that will obviously change. It appears unlikely that a vaccine will be available and licensed for use in the UK for this season, so it is very important to consider what other control measures might be supported by the results of scientific research.”
Professor Joe Brownlie, from the Royal Veterinary College said “In the spring we had three cases of deformities caused by Schmallenberg in lambs from our flock, so we wanted to see what the prevalence of infection might be in our animals.”
“We took samples from every animal in our dairy herd and sheep flock and worked with our colleagues at Pirbright to test them for the presence of antibodies that indicate a previous infection with Schmallenberg. The results indicated that approximately 3% of the animals had been infected. Then we tested the same animals again and found that although all of the positive animals still tested positive, a small number of previously negative animals are now testing positive as well.
“We also tested our very small flock of Alpacas and detected antibodies in two of the animals. This is an interesting result as Alpacas are more closely related to camels than to sheep and hadn’t been shown to be susceptible to SBV before.”
Chief Veterinary Officer Nigel Gibbens said “So far we have seen a relatively limited impact from the disease on English farms and those in the rest of Europe, but we understand that it can be distressing for individual farmers.
“The knowledge that Schmallenberg virus has over-wintered in the UK and is circulating again this year is important to be aware of. Studies so far have shown there is a good level of immunity in animals that have already been infected, so it means that the disease is infecting animals and building immunity at a time of year when the symptoms of the disease in most animals are not serious.
“As the disease is circulating, it also means that the offspring of livestock in areas that have remained uninfected until the time that animals are becoming mated are most at risk. We are monitoring which areas have had infection and which haven’t, to help farmers consider and plan for the likely impact.”
A lot remains unclear - it is not known exactly how or where the virus has survived the winter and the Entomology Group at Pirbright (led by Dr Simon Carpenter) are still to announce results of their work to confirm biting midges as a major route of transmission – but this new information provides an important impetus for future research and a basis for the development of policy and advice for farmers and vets.
The teams involved intend to continue studying the emerging threat from Schmallenberg virus and anticipate further testing during the late autumn, after the autumn calving season and during the early pregnancy period. The results of this study will be indicative of a number of other farms in the UK in which there was a low level of SBV infection last year which now appears to have overwintered and re-emerged in the current midge season.
This work, carried out as collaboration between the RVC and Pirbright, is part of a Defra-funded project to develop an inexpensive diagnostic ‘ELISA’ antibody test. Professor Mertens’ team will use samples from the RVC animals to test the procedure they are developing. The test will be produced using antibodies generated from viral proteins that have been grown in tobacco plants by Ludmila Schellenberg, a student of Professor George Lomonossof at the John Innes Centre in Norwich – another Institute with strategic funding from the BBSRC.