Tuesday, 25 June 2013

Schmallenberg virus (SBV) in ewe/cow pregnancy

Readers may remember me reporting previously on the new virus called the Schmallenberg virus (SBV) which causes fetal abnormalities in cattle and sheep. The virus was first identified in 2011 and is carried by midges which infect animals when they bite them, rather like mosquitoes can infect people with malaria.

However, in the case of SBV the problem arises when the midge bites and infects a pregnant ewe or cow. The virus then causes problems with the development of the fetus resulting in a range of deformities which may include bent limbs and fixed joints, twisted neck or spine and brain deformities. The nature of the deformity depends on when during the pregnancy the infection took place.

Studies have shown that infection is widespread throughout the UK which is not surprising as there seems very little that can be done to prevent livestock being bitten by midges. In this area I am aware of a number of clients who have reported problems with the virus and certainly the early lambing ewes seem to have suffered worse. This is because they would have been in the early stages of pregnancy during the late summer and early autumn when the midges would have been active.

This appears to be supported by the experience of local vets. For example Paddy Gordon of the Shepton Vet Group said, “We saw sporadic cases of the disease last year, however diagnostic costs mean that confirmed cases are unknown. We saw most lamb deformities in January and the majority of affected calves were seen in March and April”.

When the virus was first discovered there was no means of protecting livestock against the disease but scientists have now produced a vaccine which has been licensed for use in non-pregnant animals only. Cattle require two vaccinations approximately four weeks apart while sheep only require a single dose of the vaccine. Onset of immunity then takes place about three weeks after the last vaccination although how long immunity will last is not known and annual boosters are recommended.

However at a cost of approximately £3 per dose many farmers will think twice about treating all their livestock. In this respect Paddy Gordon commented, “Farmers will want to target the treatment on those animals which are most likely to be at risk of fetal deformities. We do not know how many animals will have developed a natural immunity to the virus and so we will have to wait and see what happens this year to fertility and calving/lambing next spring. We see the vaccine being used by early lambing sheep flocks in particular, probably smallholders with a few pet or pedigree sheep to protect and in some beef herds and maiden heifers according to concern and experience. One problem is that the vaccine has no licence for use in pregnant animals, and we would not recommend its use in pregnant animals due to the possibility of abortion due to vaccine response or stress of handling. This rules out use in most dairy herds which are all year round calving.”

So, although SBV has been nothing like as catastrophic to livestock farmers as BSE or Foot and Mouth Disease, it has certainly infected many livestock in this area we wait to see how many livestock will develop natural immunity, the long term impact of the disease on fertility and the role vaccination may play in the future.

James Stephen MRICS FAAV
Rural Practice Chartered Surveyor, Wells

T: 01749 683381
E: james.stephen@carterjonas.co.uk

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