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Bluetongue: The facts from the 2007 outbreak

Insights

Following the confirmation of a bluetongue outbreak in 2007, Jack Davies answers farmers’ concerns in a Q&A and William Surman looks at the continental experience of the bluetongue virus.

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What is bluetongue disease?

Bluetongue is a virus which affects all ruminants including sheep, cattle, goats, deer, buffalo and camels but does not affect pigs and poultry. However, its effects are most profound in sheep. The virus cannot be transferred to humans.

How is the disease spread?

The virus is transmitted by the culicoides oboletus and pulicaris midges as they bite the animal, injecting the virus into the bloodstream.

 

It is passed from midge to animal and from animal to midge, but not from animal to animal.

 

Midges are able to fly up to 2km a day, but can travel passively on the wind up to 200km.

 

Their life cycle is between 10 and 14 days – so breeding is essential to the spread of disease as newborn midges bite infected animals, contracting the virus and spreading it further. However, the virus is not passed from the mother to her offspring, so young midges that overwinter will be unlikely to have the virus when they eventually mature.

 

The disease may also be spread by the movement of infected animals, introducing the virus to midges in a new area, and can be spread in manure, where the disease can survive for long periods.

 

In sheep, the virus lasts for 54 days and in cattle it survives in the bloodstream for up to 60 days.

 

The virus does not have to be widespread in the midge population to devastate livestock. In Europe, where over 6,500 cases of bluetongue have been reported, the level of virus in midges remained relatively low. The Government’s deputy chief vet Fred Landeg said: “We have done some midge ‘studies’ that show they are a constant vector in the area – and they are midges capable of carrying the virus.

 

“We have not yet tested midges because it is rather difficult to do that at the early stage of investigation. We do know from the European experience that the level of infection in the midges is quite low.”

Where did the disease come from?

There are 24 serotypes of the virus and the one that has caused the outbreak here is serotype 8.

 

Originally endemic in Africa, due to warmer climates the virus has spread through northern Europe since its initial outbreak in 2006.

 

Its arrival in the UK is believed to have come as infected midges were carried across the channel on strong winds.

What are the effects of the disease?

The virus causes swelling of the lips and tongue, causing animals to lose their appetite. It also causes haemorrhaging and swelling around the joints, causing livestock to be uncomfortable on their feet.

 

Prof Philip Mellor from the Institute of Animal Health said there had been a 30 per cent fatality of infected sheep in Europe this year. “In cattle, the figure is much less – probably less than 5 per cent but it is highly variable.”

 

The rate of infection also varies from farm to farm, but Prof Mellor said that, last year in Europe, the prevalence of infection in some herds of cattle was as high as 80 per cent.

 

Symptoms in cattle are much less severe than in sheep and the virus can often go undetected, with cattle acting as a reservoir for the disease.

 

The disease can also cause muscle wastage in sheep, even after they have recovered. Infected cattle often suffer a reduced milk yield, though this is highly likely to be restored once the animal has recovered.

How will the disease affect farmers?

Sheep farmers should be most concerned – although some sheep do recover and their meat is safe for human consumption. However, muscle wastage can see much of the value wiped off the finished product and abattoirs may turn poor produce away.

 

During infection, milk yields in cattle can fall by as much as 60 per cent in some cases. This could see dairy cattle producing at 40 per cent yield for up to two months while they are infected.

 

There is also some evidence, yet to be tested in the field, that the outbreak in northern Europe in 2006 caused reduced fertility in some animals.

 

Further costs are also likely to be incurred in vet bills and feed costs for recovering animals.

What restrictions are being placed on British farmers?

The contingency plans for dealing with an outbreak have seen a 20km control zone set up around the initial infected premises in Suffolk, with a further 150km protection zone covering the south-east corner of England.

 

Movement restrictions have been imposed in the zones and will remain in place until two years after the last reported infection.

 

Animals within the bluetongue zone can not be transported out of the zone and animals outside of the zone cannot be transported into the bluetongue zone unless it is their final destination.

 

The strategy is designed to reduce the risk of infection by ensuring infected animals do not take the disease to unaffected areas of the country and to reduce the risk of unaffected animals coming into contact with virus-carrying midges.

 

As pigs are not affected by bluetongue, they are allowed to be moved outside of the bluetongue protection zone.

 

All restrictions and details of the control and protection zones can be found at: www.defra.gov.uk.

How will the outbreak affect exports?

Under current regulations, live exports from a bluetongue zone to a country free from infection will only be permitted through bilateral agreements, like those used by the Netherlands and France.

 

Exports of susceptible animals to other bluetongue infected countries are also banned for at least 120 days after the last recorded case.

 

Meat and meat products, however, are not affected and may still be exported.

How will the outbreak affect shows and events?

Movement restrictions will have an impact on shows and events, preventing livestock from entering the bluetongue area. As such, many shows and events in the area will not be able to take place or will have to go ahead with no livestock.

 

The situation is under constant review, taking into account the potential spread of disease to other parts of the country.

What are Defra doing in the restriction zones?

In the control zone, Defra is visiting all premises and carrying out targeted sampling, testing those animals most at risk of infection.

 

In the protection zone, Defra has stepped up its vigilance, keeping an eye out for signs that infection may have spread.

 

At present Defra has 244 staff working on the ground in the foot-and-mouth control and surveillance zones and 77 in the bluetongue zones. The deputy chief vet said that while the approach to bluetongue was different it was no less serious. He said: “We need to know where the disease is but can only investigate these cases with fewer resources and slower, without culling.

 

“It is more about surveillance and establishing how far the disease has spread. Most importantly farmers need to be vigilant and report signs of disease.”

 

Unlike foot-and-mouth the disease is nearly impossible to eradicate so efforts will be stepped up to ensure farmers can live with the virus if it becomes endemic and to step up research and development efforts in developing a vaccine.

Will there be compensation for livestock lost to bluetongue?

No, animals that die from the disease will not be subject to compensation.

Is there a vaccine?

At present there is no vaccine available, although one is expected to be available by summer 2008.

 

Vaccination is believed to be safe and should not affect the value of exports should it be used as a defence against the disease – this is

under constant review by Defra until a vaccine becomes available.

What steps can you take to prevent infection?

Farmers nearest the continent are thought to be most at risk. Farmers are warned to look out for the symptoms and report any suspected cases immediately to their local animal health office.

 

Midges are more active at lower altitudes so farmers are advised that, for example, bringing sheep onto lowlands will increase the chances of midge bites and subsequent infection.

 

Also, insecticides can be applied to livestock as well as to any manure stocks and animal housing to prevent midges from reproducing.

 

Midges lay their eggs in manure and wet soil. If manure is removed or treated weekly this should cut down the risk of infection, removing the eggs before they have a chance to hatch. Defra advises that manure piles should be either removed and placed away from any susceptible livestock, or covered with plastic sheeting.

 

Midges are most active between dusk and dawn and farmers are advised to move their livestock under cover where possible to avoid the risk of contact with infected midges. It is also advised that nets treated with insecticide be placed over windows and doors of any animal housing to prevent midges from entering and therefore cut down on the number of bites. Midge nets are available from most camping stores.

 

Defra has suggested that Deltamethrin-based insecticides are the most effective against biting midges and should be applied every 1-2 days.

 

Advice from Defra on how to protect your farm is available at: www.defra.gov.uk.

Will the virus survive the winter?

Perhaps. The virus cannot survive temperatures above 15deg C, but midges can bury deep into a sheep’s fleece to survive a cold winter.

 

The virus may also survive in manure over the winter and come back again in the summer when midges begin to reproduce.

 

A warmer than average winter is predicted this year so hopes of an early frost nipping the disease in the bud may not be realised.

 

The weather could be the UK’s best line of defence this winter as it tends to come from the Atlantic rather than from the continent. Prof Philip Mellor from the Institute of Animal Health said: “Our prevailing winds come from the west and, in actual fact, the continent is more at risk of infected midges being blown over there than we are of them coming over here. Hopefully, the wind will help and will push the midges out to the continent.”

Is the virus likely to stay?

A short winter may lead to the recurrence of the virus as it remains in the bloodstream of cattle for up to 60 days – so the midges may reappear before the last infected animal has recovered.

 

Also, a small number of midges have been known to survive the winter so while the number of cases is likely to drop over the winter months, a small number of infections could still occur.

 

Even if a cold winter kills the virus off, there is a good chance it will reappear in the warmer, wetter months whether it has survived the winter or, alternatively, comes in again from the continent.

Are there more diseases to come?

Bluetongue may just be the first of a series of midge-borne diseases to hit the UK. African horse sickness virus is a closely related disease and is also more dangerous – killing over 90 per cent of horses it infects. It has already hit Spain and is likely to invade northern Europe as the climate gets warmer.

What does the future hold for the UK?

Experts say Britain will have to ‘learn to live’ with bluetongue for a significant length of time. Fred Landeg said: “It is likely that during October and well into November we will see significant numbers of new disease cases. It is also likely that the disease will re emerge next year.”

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