An emerging livestock disease caused by the Schmallenberg virus that was first detected in Germany late last year has been causing deformities in newborn lambs, goat kids and calves on farms in Belgium, Germany, the Netherlands, and now the UK.
Schmallenberg – named after the place in Germany where the first sample of the virus was identified – causes deformities and still births in sheep, goats and cattle but does not have major clinical signs in adult animals, making it quite difficult to spot.
Schmallenberg virus was first identified in the UK on 22 January 2012 and by 31 January was identified on 11 farms in the South East of England (Suffolk, Norfolk, Kent, Essex and East Sussex). So far it has been identified in newborn and stillborn lambs with limb and spinal deformities. Larger numbers of lambs and a few calves have already been affected elsewhere in Northern Europe. The congenital defects that are being seen now are caused by infection of the pregnant ewes or cows late last year so there is nothing that can be done to prevent them. However, we must still be concerned about the possibility that the virus will survive through the winter to cause future infections.
So far the disease has had only a limited impact in the UK, with cases found during early lambing, so it is difficult to say with certainty what percentage of lambs or calves will be affected by the virus this year. Recent experience by veterinary colleagues in mainland Europe shows that up to 25% of lambs born in a one infected flock had significant or severe congenital defects of their limbs or central nervous system.
Professor Peter Mertens, head of the Vector-borne Diseases Programme at the Institute for Animal Health said "We will study this disease and the virus that causes it in a number of ways. One major priority is to put in place reliable test systems, so that we can detect the genomic RNA of the virus and virus specific antibodies. This will allow us, to test and identify infected animals or insects, as well as helping Defra, AHVLA and other stakeholders with what might end up being quite a high volume of samples from suspected cases."
Researchers at the Institute are working with colleagues elsewhere in Europe. In particular the Friedrich Loeffler Institute has already provided the nucleic acid based assay (Real-time RT-PCR) which is being implemented by the IAH Non-Vesicular Reference Laboratory, which also tests for bluetongue, African horse sickness, and African swine fever, among others.
The pattern of transmission of this disease is in some ways similar to that of bluetongue, which is caused by an unrelated virus that is carried by biting midges. It is currently thought likely but not yet confirmed that Schmallenberg virus can be transmitted by the same insect species. IAH has colonies of midges and mosquitoes that will be used to confirm if the virus does indeed infect these insects, which can then transmit it between animals.
Dr Simon Carpenter, research leader in entomology at IAH said "Samples of the virus have just arrived at Pirbright from colleagues in Germany. Using Insects from our colonies we will be able to see if midges or mosquitoes can become infected by Schmallenberg virus. This will allow us to tailor our advice to a wide range of stakeholders, including livestock owners who could be affected by the virus in 2012 and also to understand some of the factors driving the outbreaks."
If Schmallenberg is confirmed as a midge-borne virus, IAH’s expertise and experience concerning the epidemiology of bluetongue virus will be invaluable. It was thanks to the combination of disciplines including virology, entomology, meteorology, and mathematics at the Institute that the arrival of bluetongue in the UK in 2007 was predicted, allowing for measures to be put in place to prevent a major outbreak – work that is estimated to have saved the UK economy £485 million. IAH and the Met Office are already collaborating in the planning stages of work concerning Schmallenberg virus.
Dr Simon Gubbins, research leader in Mathematical Biology said "If Schmallenberg is midge-borne – and it does look likely that it is – we can begin to learn more about how it is passed on. That helps us in two important ways: it means we can make predictions about how it might spread in the future and therefore consider whether there are suitable control methods which may lessen the impact. It will also tell us something about where it came from.
"When a new disease emerges like this, it is an opportunity for us to understand what has happened, allowing a virus to change so that, for example, it infects a new species, or is more infectious than before. Schmallenberg has been a complete surprise but by studying it, we hope that in the future we will be better placed to predict the scenarios where new diseases might emerge."
It will now be a matter of waiting to see how seriously the UK and Europe are affected by this disease and in the meantime IAH and colleagues across Europe will be working to learn as much as possible about how to detect and control its spread.