Treating sheep for Schmallenberg virus

Schmallenberg virus (SBV) was first seen in parts of Germany in 2011 and is named from the German town it originated.

It was diagnosed in southern England in March 2012 and the first Irish cases were seen in October 2012.

There were few reports of the virus from 2014-2016 but it has re-emerged this spring 2017 and it may be useful to remind ourselves of the features of the disease.

While there is really very little that can be done to reduce the impact of the disease if it arises in a sheep flock, it is useful to be aware of the possibility and causes of the disease. There was a lot of concern about the disease with a number of incidences in Ireland in 2012 and 2013, but, for whatever reason it has not been the issue that was feared when it first occurred.

However, there appears to be reason to believe it may be on the increase in Ireland once more.

There have been some cases confirmed in cattle to date with a number of other cases being investigated. It is therefore likely that sheep will also be affected by the disease.

Schmallenberg virus is spread by the culicoides midge so the disease can only be spread during the period when the midge is prevalent.

The virus infects the foetus of animals infected during the early stage of pregnancy normally in the second and third months.

This may lead to abortion, stillbirth or the birth of weak, malformed new-born lambs.

In sheep, the main clinical signs of SBV are the birth of lambs with deformed and fused limbs and spine and reduced development of parts of the brain. Many require to be delivered by caesarean section which adds to the economic impact of the disease.

Where infection in sheep occurs at around days 30 to 70 of pregnancy this appears to be the critical time for abnormalities to occur in the developing foetus.

When the weather is mild at that time, there is an increased risk that the midge which carries the disease will be active and therefore will spread the virus.

Early lambing flocks appear to be at greater risk than flocks lambing mid-season however farmers with flocks lambing over the next few weeks should be aware of the possibility of cases occurring.

For mid-season lambing flocks, where mating took place from October to mid-November, the risk period for infection by the midge is from early November to late January. Midges would require mild conditions in this period to be airborne and would also need to carry the virus.

As mentioned, the main clinical signs of SBV are the birth of lambs which have deformed and fused limbs and spine and reduced development of parts of the brain. As with all animal health concerns farmers should consult their veterinary practitioner if they have suspicions or concerns of SBV cases around lambing time.