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January 31, 2012
The AHVLA reported today that it has now confirmed the presence of Schmallenberg Virus on 11 sheep farms in the UK. The disease has also been found in Belgium, Germany, and the Netherlands.
What do we know about Schmallenberg virus?
It’s named after the town of Schmallenberg, from where the virus was first isolated. The virus (SBV) is an Orthobunyavirus, a large group of viruses, most of which are spread by biting insects and cause diseases of cattle (Wikipedia has a list, if you’re interested), although a couple of species cause encephalitis in humans. SBV has been found in cattle, sheep, and goats. In adult animals it causes fever, loss of appetite, a reduction in milk production, and sometimes diarrhoea, although the symptoms only last for a few days. More worryingly, though, are the effects on the offspring of infected animals – abortions and stillbirths of young with brain and limb abnormalities (torticollis, arthrogryposis, and hydranencephaly). We saw the clinical signs in adult animals in Europe during the summer, and now we’re seeing the deformed offspring in the UK and the continent.
Is that all?
Pretty much! All the rest is based on behaviour of related viruses, and what we have (and haven’t) observed.
So what are our best guesses about SBV?
- It’s most likely spread by biting insects (this is called vector transmission), probably midges
- It’s probably no risk to human health
- The cases in the UK are likely due to infected vectors blowing over the channel, in a similar manner to bluetongue
- There are probably more infected animals than we are aware of
What don’t we know that we’d like to know?
- Can it infect other species? Other ruminants would be obvious possibilities
- What’s the geographic spread of this disease?
- What insect species is/are competent vectors?
What happens now?
Work is ongoing to try and develop good tests for SBV; particularly a test that would identify animals that have been exposed to it would give us a much better idea of how far the disease has spread and what its prevalence is. Similarly, researchers will be trying to find out the basic epidemiology of SBV, so that control measures can be devised. Animal keepers are being encouraged to look out for deformed newborn, stillborn, or aborted ruminants, and to report them to the relevant authority (AHVLA in the UK). It’s going to be interesting to see how the situation develops; given how mild winter has been so far, we might well expect higher midge numbers this year, which I’d expect to increase the spread of SBV.
If you want to know more, DEFRA is publishing updates on the situation here.