Swan with bird flu thought to be from outside UK - UK - The first wild bird found in Britain with the H5N1 bird flu virus is from a migratory species, the country's chief veterinary officers said on Tuesday, but they did not say where it had contracted the virus.

The conclusion boosts hopes in Britain that the infected swan may be an isolated case and that the virus may not have become established in domestic wild birds. Experts said it was also possible that the infected swan died at sea and washed up on the Scottish coast. Officials initially said that the bird found dead in Cellardyke harbour in eastern Scotland on March 29 and later found to have the lethal H5N1 strain was a Mute swan.

The Mute swan does not generally migrate, leading to fears that the disease may already have spread to native bird populations. However, DNA tests have now identified the bird as a Whooper swan. Whoopers breed in Iceland, Scandinavia and northern Russia and spend the winter in Britain and parts of continental Europe. "Our current hypothesis is that the swan originated outside Great Britain," the vets said in a statement.

The Cellardyke swan is the only wild bird so far found in Britain to have the H5N1 virus, which has led to the death and culling of some 200 million birds since late 2003. Martin Fowlie, of the British Trust for Ornithology, said the bird may have wintered in continental Europe and have died while making its way back to Iceland to breed.

It may have died in Scotland or over the North Sea and have washed up on the Scottish coast, he said. "Another possibility is that it was a bird that wintered in the UK and contracted the virus from another bird before moving north," he said.

Bob McCracken, a former president of the British Veterinary Association, said that if the swan died far out at sea then the bird population around Fife in Scotland could be free of H5N1. "However, if the Whooper swan was alive and infected on the shores of Great Britain, then we must accept that other birds in the Fife area may also have acquired infection," he said.

"This latter scenario is the one we have to focus on -- we need to assume the worst until we can prove otherwise," he said. Scientists fear bird flu could become highly dangerous to humans if the virus mutates into a form easily passed on from one person to another. It has so far killed 109 people since late 2003, most of the victims in Asia.

Scotland's chief medical officer Harry Burns has said the risk of the virus passing into humans is extremely low. Scottish officials have taken steps to prevent the spread of the disease to domestic poultry farms.

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