S-T-U

Schmallenberg Virus

History of the Disease

In 2012 a new viral disease spread through the UK affecting cattle and sheep. The virus was first discovered in Southern Germany and spread northwards through Europe via midges. The infection of sheep and cattle was widespread.

Symptoms

In sheep there are no obvious symptoms in the adult sheep. In cattle the common symptoms are milk drop, increased fever and diarrhoea. Many animals will be affected and may not display symptoms. Any viral infection has a potential to impact on fertility. The most striking impact of SBV is by producing deformities of the fetus. Infection in early pregnancy can result in spinal deviation, twisting of the neck and fusion of the joints in extended or contracted positions. The window of infection in cattle is between 2 and 5 months. The infection however appears to deliver a deformity in 1 in 200 cases in cattle so the proportion of the fetuses affected is small. In sheep flocks the level of infection can be considerably higher. Typically early lambing flocks are most severely affected as the stage of pregnancy often coincides with the peak midge activity and infection rate.

The distortion of the fetus will cause lambing and calving difficulties. The contraction of the limbs and the inability to straighten the deviated spine often requires a caesarean section for the calf to be delivered successfully.

The overall dimensions of the calf may require a much longer incision in the uterus for the fetus to be delivered. Typically the calf or lamb is delivered full term

In some instances an embryotomy may be possible but this is challenging procedure to under take as the extent of the deformities are not known.

 

The calf to the right was presented with its head  upside down and the forelimbs tucked back. On closer examination the joints could not be extended. A caesar was successfully performed and by using an extensive incision the calf was successfully removed with no adverse affect to the mother. All 4 feet were presented at once.

What can you do to prevent SBV?

SBV appears to come in 4-6 yearly cycles. In 2012 the virus spread rapidly within herds and flocks in Leicestershire. This resulted in widespread immunity. The virus load of SBV within the midge population is high and consequently most animals became immune to the disease. The impact of the disease in the following years was minimal. By late summer 2016 there was a marked decline in herd immunity and animals born in the period 2013-16 were susceptible resulting in another round of infection. The animals most at risk are those not exposed in 2012 i.e.  younger animals and any animal with a partial immunity.

The calf to the right was presented in full breech presentation and was unable to be corrected. A caesarean was required to deliver this calf. The cow made an excellent recovery.

What about vaccination?

Vaccines were produced in 2013 in response to the outbreak in 2012. However vaccination uptake was limited and as such it was uneconomic to produce the vaccine again. The major uptake in vaccination was in early lambing flocks.

What can I do to limit the impact of SBV?

The major impact is within early ( January ) lambing flocks. Typically deformities are only found in a small proportion of calves( 0.5-1%). More research is required to investigate the wider impacts of the disease. Anecdotally the impression we have is that SBV has a direct impact on milk yield and short term impact on fertility ( re-absorptions/ conception rates). Any viral infection will also make any affected animal more susceptible to any other diseases ( e.g Mycoplasma pneumonia) . Dummy calves and general brain damage has been reported in young calves/ lambs due to infection and damage to the central nervous symptoms.

The economic impact of SBV however is much lower than viruses such as BVD as the virus appears to infect the herd rapidly and then the animals become rapidly immune.

There is currently a limit to what can be done. In 2017 the most likely problems will occur in younger animals who were in mid pregnancy during the peak exposure to virus in  summer/ autumn 2016.

Take particular care with calvings and lambings. If you find something you are not sure about phone the practice for advice/ assistance.

Further Reading

Review Article on SBV