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Friday, 2 March, 2001, 01:49 GMT

Cold spell link to foot-and-mouth

Freezing weather conditions are not helping the epidemic

By the BBC's science and technology correspondent Christine McGourty

The cold weather may be contributing to the rapid spread of the foot-and-mouth outbreak in the UK, according to scientists.

They believe the original source may be in meat illegally imported from a country where the disease is endemic, perhaps in Asia, South Africa or South America. The virus is one of the most infectious found in any animal.

"If the virus infects a cell, within a couple of hours that cell can be changed from a normal one to something that bursts open, releasing about 100,000 virus particles," said Professor David Stuart of Oxford University.

"This means you can get spread from one animal to another in a herd very rapidly. By the time the disease appears in one cow, it's likely that the whole herd will have got the disease."

Professor Philip Duffus, of the Bristol Veterinary School, said the weather conditions were not helping.

'Likes the cold'

"The problem with this virus actually is it quite likes the cold, so the weather at the moment is not conducive to its termination.

"What it doesn't like is being dried and it hates ultraviolet light, so sunlight will very quickly kill this virus as will heat."

It is thought that in an outbreak in the Isle of Wight in 1981, the virus was borne on the wind from Brittany, France. But this time, scientists say it is unlikely to have arrived from any of England's near neighbours.

A more likely source is in cheap meat illegally imported from one of the countries affected by the disease.

Professor Duffus said: "The 1967 outbreak was traced back to a leg of lamb from Argentina, which was brought in with the virus in its bone marrow, eventually fed to pigs, and bam!

"That's traditionally how the outbreaks in this country happen and I would bet that's how this outbreak happened."

Country to country

He believes that once the current outbreak is under control, questions will have to be raised about the globalisation of the meat trade.

It was "crazy", he said, to import meat and meat products from countries where foot-and-mouth disease is endemic.

Scientists should be able to trace the source of the virus. It evolves quite rapidly as it moves from country to country, so studying its genetic make-up ought to reveal the country of origin.

One problem, however, is that a number of countries do not admit to having the disease and do not send samples to the experts at Britain's Institute for Animal Health, who have been studying the different strains involved.

At the institute, scientists have already discovered the virus is almost identical to one that has been causing a pandemic disease throughout much of Asia for the last few years.

Vaccine problems

"For instance, there was an outbreak of foot-and-mouth disease in Japan last year," said Professor Stuart. "It was the first time they'd had it for 70 years.

"The virus spread to South Africa and South America, so this is a very virulent form of the virus."

Vaccines do exist against the disease, but they bring their own problems. A vaccinated animal produces antibodies in its blood system that protect it against the disease.

But an infected animal produces the same antibodies. So a country testing imported animals would not easily be able to tell if they had the disease of if they had simply been vaccinated.

That problem could be overcome, said Professor Stuart, but it would take time. It also takes several weeks for the vaccine to become effective in an animal, he said. And as the virus spreads so quickly, the whole of the UK herd would have to be vaccinated immediately for it to be useful.

'No quick fix'

Finally, though the virus does not cause disease in vaccinated animals, it can still produce a persistent infection, which can sit latent in the animals for up to a year.

"If the animal is subjected to stress, transported around perhaps, then the disease can come to the surface again and that animal would then be the potential starting point for another outbreak of the disease," said Professor Stuart.

Professor Duffus agrees that vaccination is no quick fix.

"Once we start vaccinating, in my opinion, in terms of animal products, we almost become third world. No-one is going to want our products, no-one is going to want our live animals and no-one is going to want our breeding stock.

"This country still has a great tradition in producing high-quality animals. We can't throw this away."