Last updated 22:02, Tuesday, 04 March 2008

Defra has ordered 22.5 million doses of a killed bluetongue vaccine, out of which 20 million doses have been reserved for use in England.

Vigilance: Cattle are more important reservoirs of the disease than sheep

The current cattle population of England is estimated at 5.5 million and the sheep population is about 15.5 million. If all of these were to be vaccinated, 26 million doses would be required.

Vaccination is proposed to be voluntary. Two doses three to four weeks apart will be required to protect cattle; sheep will need only a single dose. It is thought that an annual booster vaccination will be required.

As we approach the end of the vector-free period, concern over the disease grows.

The NFU recently hosted a meeting where local Defra officers presented their unfolding plans for bluetongue control, including vaccination.

What is bluetongue?

Bluetongue is a viral disease that is transmitted by blood-sucking midges that have previously fed on an infected animal.

The strain found last year in East Anglia has been in northern Europe since 2006. It didn’t die out in the winter of 2006/7 and became a much larger outbreak in 2007.

What animals does it affect?

It can affect sheep, cattle, goats and deer, but not horses, pigs, birds, humans, dogs or cats.

Sheep are the most likely to show signs of illness when infected, but cattle are more important reservoirs of disease. Midges seem to feed more easily on cattle and an infected cow will carry the virus for longer and will feed and infect many more midges than an infected sheep.

How does it affect them?

Despite its name, a blue tongue is a relatively uncommon sign. A diseased animal will typically show signs three to four days after being infected by a midge.

Sheep may be fevered and off food. There may be excessive slavering. There may be redness and ulcers in the mouth. The head, lips and tongue may become swollen.

In some cases there may be redness and inflammation at the boundary between the hoof and the skin.

It could be confused with more common conditions such as orf, photosensitisation and footrot.

Animals that recover may take four to six weeks to recover fully.

Other affects can include abortion rates of 5 per cent and long-term sterility in male animals.

Do all infected animals show signs of illness?

No, many cattle will show no signs of illness at all. Many sheep also become infected without showing obvious signs, although it is more likely that some infected animals within a flock will show signs of disease.

In Belgium in 2007, 26 per cent of the national flock showed signs of disease with 10 per cent mortality in the national flock.

In the few UK cases last year there were typically two to three ill animals on affected farms. Subsequent blood testing revealed that 16 per cent of cattle and 5 per cent of sheep had been infected on these premises.

Where do midges come from?

Midges are found in high numbers wherever livestock are present. They breed in soil and manure heaps. They have a variable lifespan of two to 12 weeks depending on conditions.

What are all these Defra zones about?

You will need to know the Defra jargon to understand the various movement regulations and know whether your holding is eligible for vaccine.

The ‘protection zone’ is an area of at least 100km surrounding a confirmed bluetongue case. Only herds within this zone will be permitted to use bluetongue vaccine when it becomes available.

The ‘surveillance zone’ is a zone of at least 50km beyond the boundary of the protection zone. Herds/flocks within this area are subject to movement regulations but will not, at present, be permitted to vaccinate. They will subject to closer monitoring.

‘Restricted zones’ is a general encompassing term used to describe the protected and surveillance zones together.

The current ‘bluetongue-free zone’, which includes Cumbria, is not subject to movement restrictions and will not at present be permitted to vaccinate.

The ‘vector-free period’ is the winter period when scientists regard transmission of bluetongue improbable and movement is allowed out of restricted zones subject to animal testing and licensing. Even when midges are present they do not appear to be able to harbour the virus at low temperatures.

This winter’s vector-free period started on December 21. Defra recently announced it will end on Saturday, March 15.

How might it arrive on my farm?

An animal may be purchased from the bluetongue-free zone but already be infected. This animal can then infect your resident midges.

Alternatively, an infected midge may fly, be blown or be transported in a vehicle from a farm which has already acquired infection.

Will bluetongue be like foot and mouth all over again?

Thankfully, compulsory slaughter, burning pyres, endless disinfection and farmers living in solitary confinement will not be a feature of bluetongue. These measures will have no impact on this disease. It could, however, cause great losses if it arrives and vaccine is unavailable.

How can I protect my stock?

If bluetongue enters Cumbria, it is difficult to see how any control other than vaccination can safeguard our flocks and herds.

Midges are widespread wherever livestock are present and total extermination is impractical. Reducing midge populations by insecticidal treatment of livestock and management of slurry/manure may reduce the speed at which the disease will spread. It may be a useful exercise while waiting for immunity to be produced after vaccination.

When is the risk highest?

Within a year, the period of highest risk is late summer and autumn when the midge population is at its highest. Within a day, midges tend to feed at dawn and dusk primarily.

What can I do?

Be vigilant. Contact your animal health office if you have an animal with suspicious signs.

Remember, one farmer spotting a case in a surveillance or free zone will give everyone within 100km the opportunity to protect their stock by vaccination before the disease strikes.

Take the earliest opportunity to vaccinate if your holding becomes eligible. If no vaccination is immediately available, insecticides may buy you some time.