Viewpoint: Schmallenberg virus

Professor Wim Van der Poel is based at the Central Veterinary Institute, Wageningen University in the Netherlands and is a Visiting Professor at the University of Liverpool. He has a special interest in new and emerging viruses, and he has been involved in Schmallenberg virus infection across Europe since its discovery last autumn.

Professor Van der Poel said: “Since the discovery of Schmallenberg virus in November 2011, the spread of the virus has now resulted in malformed new-born lambs and calves on farms in at least five European countries. Veterinary institutions in all of these countries have put significant effort into the development of diagnostic tools.

“Now RT-PCR virus detection methods have been put in place, the focus has moved to the development of antibody tests, which are indispensable for the much needed epidemiological surveys, including the detection of infected adult animals over the summer that will largely show no disease signs.

“There is good cooperation between institutions in Europe: research plans are combined and materials and protocols are being exchanged. In the meantime a lot of research work has been done on characterization of the isolated viruses. The elucidation of the virus genome and further comparison studies, have confirmed that Schmallenberg virus is a member of the Simbu serogroup of the orthobunyaviruses. The ECDC risk assessment for public health, which was made in Dec 2011 based on genetic relationships of the virus, still holds. The risk for public health can be regarded as extremely low.

“Since the virus is assumed to be transmitted by insects, and especially midges which are not active in winter, there probably is no virus circulation at the moment. All malformed calves and lambs born recently were infected during gestation, most likely in late autumn 2011. In sheep on mainland Europe the number of malformed new-borns is already decreasing. In cattle, due to the longer gestation period, this number is still rising and we will have to wait for another month or so and see how high this will go.

“The Netherlands is the only country in which the disease has been made notifiable. This has helped us to get a good early picture of the outbreak, but unfortunately there is not much we can do to prevent the disease. Midges are very difficult to control and there is no vaccine available. At best the development of a new vaccine will take at least 18 months.

“If the virus survives over the winter, midges will start biting again in spring and there may be a further spread over Europe. While affected countries within Europe are working on disease surveillance, other member states fear introduction of the virus and are trying to put diagnostic tools in place as soon as they can.

“Several countries outside the EU have imposed import restrictions for live animals and genetic products, and the scientific committee of the World Organisation for Animal Health (OIE) has endorsed a set of recommendations for trade. All of this challenges the European Union to set up proportionate and effective control measures, and member states’ scientific institutions have been asked to rapidly produce scientific results to ensure any measures are evidence-based.

Despite enormous efforts already made by the responsible authorities, veterinarians and researchers, Schmallenberg virus will continue to keep us very busy to at least the end of the year.”

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