Bird flu was found on a duck farm in England on Monday days after it was discovered in Dutch chickens, forcing authorities to destroy poultry and restrict exports, although it was not a strain known to be deadly to humans.
Health officials said the outbreak may have been brought to Europe by wild birds migrating from Asia where millions of South Korean farm birds have had to be destroyed.
"A species of wild swans might be carrying the virus without showing signs of disease," said the European Commission after adopting emergency measures to contain the outbreak that mirrored those already taken by Britain and the Netherlands.