Schmallenberg virus (SBV) is a virus identified in Europe in 2011 that affects sheep, cattle and goats.
Animals exposed to the disease seem to develop immunity, making it likely that disease will die out in areas where the disease has been present. This is a relatively low impact disease. However, in a small number of flocks and herds it can have a significant impact.
SBV is not notifiable in the UK and no restrictions are placed on infected premises.
There is evidence from Great Britain and Europe that many animals have been infected with SBV without any clinical signs being detected. Typically, the impact in most herds or flocks affected by SBV has been low, although some farms have reported more significant effects.
Related viruses are known to stimulate a strong immune response, which then protects infected animals from subsequent ill effects. This means that they do not usually give birth to further deformed offspring. It is expected that in the long term SBV will behave in a similar manner, although monitoring will continue as SBV is a relatively new disease.
In adult cows acute infection results in diarrhoea, fever and reduction in milk yield, with a full and rapid recovery over several days. Affected herds typically see outbreaks of disease lasting two to three weeks, but the possibility of other patterns of disease occurring in a herd should be considered. This stage of the disease has not been noted in adult or growing sheep, although there is anecdotal evidence of milk drop in milking sheep in Netherlands.
New-born animals and foetuses
The second presentation of the disease is associated with abnormalities in animals born alive or dead at term or aborted following infection of the dam, affecting mainly sheep but also cattle and goats. Malformations can include bent limbs and fixed joints (arthrogryposis), twisted neck or spine, a domed appearance to the skull, short lower jaw and brain deformities (fluid-spaces in the brain, abnormally small brain parts (such as cerebellum and brainstem) and marked damage to the spinal cord. Some animals are born looking normal but have nervous signs such as blindness or a ‘dummy’ presentation - uncoordinated movement, recumbency, an inability to suck and sometimes convulsions. It is suspected that the degree of foetal deformity depends on when in pregnancy infection occurred.
How Schmallenberg is spread
Typically orthobunyaviruses are primarily spread by biting insects, such as midges, however the routes of SBV transmission have yet to be confirmed. The potential for direct transmission (i.e. from one animal to another) is thought unlikely. As midges are believed to be the major route of transmission, it is expected that significant spread is less likely during winter, when midges are usually much less active.
There is a vaccine but due to lack of demand from within GB industry, the Scottish Government believes it is not currently being manufactured. Livestock farmers should seek veterinary advice if they are considering vaccinating stock against SBV.
Human health implications
A Europe-wide risk assessment concluded that Schmallenberg virus is very unlikely to cause illness in people. No human cases have been detected in any country, and the most closely related viruses cause only animal disease.
Biosecurity is about being aware of the ways disease can spread and taking every practical measure to minimise the risk of disease spreading. The advice details practical things you can do on your farm to help prevent the introduction and spread of Schmallenberg to and from your animals.
- First published
- 29 October 2018
- Last updated
- 10 June 2021
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