Vet Emily Gascoigne discusses the rise in cases of bluetongue virus as the weather warms up. Wendy Short reports.

The bluetongue virus infection has largely affected sheep in South-East England to date and while northern flocks are considered low risk, the disease is notifiable and the previous vaccine is ineffective against the current strain.

Vet, Emily Gascoigne, asks flock owners countrywide to be vigilant, as temperatures start to rise in the coming months.

It is difficult to estimate the risk of bluetongue virus (BTV) to the region’s sheep flocks, as the weather plays a major role in disease transmission. Flocks will be at their most vulnerable as the midges, which act as the disease vector, become active in warm weather, said Miss Gascoigne, of Synergy Farm Health.

BTV is transmitted by biting midges and affects all ruminants, including cattle, sheep, goats and deer, as well as llamas and alpacas, she explained. While the disease is not 100 per cent fatal, high losses can be sustained.

“In sheep, the virus can cause a range of symptoms, with the primary indicators sometimes described as the three Fs: fever, face and feet,” she said. “The high body temperature caused by the infection can lead to abortion in ewes, so a mild spring will increase the risk and the warm, wet winter weather may have favoured biting midge populations.

"The current strain is classified as virus three and the vaccine that was used to treat the previous strain, virus eight, will have little or no effect.”

Most adult sheep will show only mild clinical signs, with some showing no evidence of infection. However, sheep and goats tend to be more severely affected than cattle. The virus disrupts blood flow, she said.

“The skin may be reddened, with other typical signs including swelling of the mouth, head and neck. It can be accompanied by mucus discharge, drooling, mouth ulcers and breathing problems.

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"Swelling may also be visible around the coronary band, where the skin of the leg meets the horn of the foot, leading to lameness, and an infected sheep will be running a fever. Mortality rates can vary widely, from as little as two per cent and up to 70 per cent of infected cases.”

Control zones to prevent the movement of sheep from areas where infection has been confirmed have been introduced in some parts of the country. Where BTV has been identified, movement restrictions have been applied and these have included the surrounding area, so anyone buying sheep from the South-East will need to take this into consideration. If BTV spreads further up the country, it is highly likely that the restrictions will follow.

Emily said: “It is worth making adjustments to increase biosecurity measures and, as with all diseases, maintaining a high standard of cleanliness is also important. Livestock exports have been severely disrupted, as a result of the BTV outbreak.”

BTV is sometimes confused with Schmallenberg virus, but the two diseases are different. Their main similarity is that both are transmitted by midges. It is unrealistic to attempt to control insect levels and while housed animals have some protection, keeping ewes and lambs inside during the turnout period is impractical, said Miss Gascoigne.

It is worth noting the typical symptoms of BTV in cattle, as many producers keep more than one species, she added.

“Cattle may appear lethargic and they can also have crusty erosions around the mouth and nostrils, with nasal discharge. There may be a reddening of the mouth, eyes and nose, as well as the skin above the hoof, along with a depressed appetite.

"Cows can show reddening and erosions on the teats and there is likely to be a dip in yield for milking animals.”

It is extremely difficult to predict how BTV might develop in the region in the future, said Emily.

“The first step for flock keepers who suspect that their sheep may be infected is to contact the farm vet, who has a duty to contact the Animal and Plant Health Agency. The vet will also advise on any action that will need to be taken, following confirmation of the clinical signs.

“The disease does not affect human health or food safety, but nevertheless it is vital that control measures are put in place as soon as possible. BTV poses a serious potential threat to the UK sheep industry,” she concluded.