What is bluetongue, and does it spell disaster for farmers?
Published 25/09/2007 | 08:24
Is it as bad as foot-and-mouth? What can be done to control the disease? Jeremy Laurance asks The Big Question
Why are we asking this now?
A shabby coated Highland cow called Debbie on a children's petting farm near Ipswich was confirmed at the weekend as Britain's first case of bluetongue disease, caused by a lethal virus which has killed millions of farm animals on the Continent. This was followed by confirmation yesterday that a second cow at the farm had contracted the disease. The discoveries raise fears that the disease could become established here, delivering another blow to farmers already reeling from the foot-and-mouth outbreak and the summer floods.
Why is the disease called bluetongue?
It is caused by a deadly virus spread by midges that mainly affects sheep, but can also infect cattle, goats, deer and other ruminants. Symptoms include swelling of the head and the neck, lameness, internal bleeding, and ulcers of the mouth, nose and eyes. The tongue may turn blue under pressure created by the swelling, giving the disease its name. The virus has infected nearly 3,000 animals in northern Europe since July, where the death rate has been about 30 per cent. Unlike foot-and-mouth, it does not spread from animal to animal but is instead transmitted by midges, which bite an infected animal and then transfer the virus to an uninfected one.
Is it as bad as foot-and-mouth?
It depends how you look at it. It is worse for sheep, killing up to 70 per cent of flocks and causing a painful, lingering death. Infection in cows is often symptomless but can still lead to spread of the disease. There is no risk to humans. Although it is more lethal than foot-and-mouth it is not contagious and does not spread from animal to animal. Instead of sweeping through farms, destroying herds and flocks, bluetongue spreads more slowly, but there is no reliable way of containing it. Culling of animals is useless against a disease spread by insects and is not normally carried out, except for welfare reasons.
Where has the disease come from?
There have been a series of outbreaks of bluetongue in the Netherlands, Belgium, western Germany and northern France since August 2006. The virus has infected nearly 3,000 animals in northern Europe since July. The Department of Environment, Food and Rural Affairs (DEFRA) warned last month of the risk of the disease spreading across the Channel and urged farmers to be vigilant. The type of virus identified in the infected cow on Baylham Rare Breeds Farm has been confirmed as the same as that circulating in northern Europe - serotype 8. The virus originated in southern Africa, where it is spread by a different species of midge. Global warming has been blamed for its spread north to the Mediterranean and southern Europe and then to northern Europe.
How did the virus get here?
The midge responsible for spreading the virus in northern Europe is the Culicoides species, which is capable of flying 1.5 to 2 km a day, according to Defra. However, if wind conditions are favourable, it may travel as much as 200km, especially across water. Prevailing winds from infected regions across the Channel are likely to have blown the midges into Suffolk.
Is the bluetongue outbreak in Ipswich confirmed?
Yes. Debbie was thought to be the only animal to have been infected, and a single case does not count as an "outbreak." But other animals on Baylham Rare Breeds Farm were tested and one produced a positive result yesterday. Specialists believed it was unlikely to be confined to a single animal, pointing out that a cloud of midges is likely to have come across the Channel and that more infected animals may yet be detected.
Professor Peter Mertens, a Government scientist, said: "What are the chances that only one midge has blown across from northern Europe and just happened to pick on this one animal? This is an animal on a petting farm which I imagine was under intense scrutiny. There are a lot of other animals out there in fields and pastures that have much less scrutiny."
What happens now that it is confirmed?
All movement of livestock is likely to be banned in a zone 20 km around the infected farm, with two further zones declared – a protection zone at least 100km around the outbreak and a surveillance zone at least 50km. Movement of livestock outside these zones will probably be banned, although it would be allowed within them. The countryside is not expected to be closed off, as with foot-and-mouth.
Infected animals can recover, and there is no reason why their meat should not be eaten. But milk yields can drop by 40 per cent and some animals suffer muscle wastage and may not be accepted by abattoirs for introduction to the food chain. Meat from infected animals would be banned from export.
What can be done to control the disease?
Mass slaughter to eradicate it is not an option as that will not eliminate the midges. The only control measures available to farmers are to spray insect breeding sites such as manure heaps with insecticide, and douse livestock with insect repellent to reduce the number of midge bites. But these measures would at best reduce the level of infection rather than eliminate it.
Keeping animals in sheds at dawn and dusk, when the midges are out in force, has not been shown to be effective, according to Defra. The only other defence is vaccination. But there are currently no effective vaccines against bluetongue in Europe. Vaccines developed for use in sheep in South Africa, where the disease originated, cause severe side effects in European breeds.
European versions of the vaccine have made the problem worse because the live virus used in the vaccine has combined with the circulating virus to create new strains. But a vaccine based on inactivated virus is being developed and is expected to be ready by next summer.
Is there anything else that farmers can do?
Pray for winter. The midges cannot survive below 15 degrees centigrade, and most experts are pinning their hopes on the fact that the Ipswich case has happened at the end of the summer rather than the beginning, with the propsect of cooler weather on the way. That would reduce the risk of the disease spreading. Peter Kendall, president of the National Farmers' Union, said: "We are hoping a vaccine will be available shortly, probably in the next year or so. If we can contain it now it need not have an enormous impact on UK farming."
After foot-and-mouth, is bluetongue the final straw?
It kills up to 70 per cent of sheep flocks and infects cattle and other animals, leading to muscle wastage and a fall in milk yields
Once established, it is impossible to eradicate by culling because it is spread by insects
It has come at the worst possible time after the summer floods and the recent outbreak of foot-and-mouth
Although an outbreak has been confirmed, death rates may be lower than the worst-case scenario, and infected animals can recover
The arrival of winter should kill off the midges, which cannot survive in cold weather, thus giving farmers a breathing space
A vaccine is being developed to prevent infection and could be ready by next summer