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.

A spokeswoman at Britain's Department for Environmental, Food and Rural Affairs said the public health risk was very low and there was no risk to the food chain.

Bird flu was also found on farms in Germany earlier this month. Authorities have yet to determine conclusively whether there is a link between the German, Dutch and British outbreaks, or whether they are related to outbreaks in Asia, but suspect that all are linked.

The German and Dutch outbreaks are of the H5N8 strain, which is highly contagious in birds. H5N8 has never been found in humans, unlike H5N1, which has killed 400 people mostly in Asia and the Middle East since 2003 and caused a global scare.

British authorities said the flu found there was also not H5N1, although they had not yet determined whether it was H5N8. The European Commission said later it probably was H5N8.

The measures being taken "have been effective in the past to contain outbreaks of highly pathogenic avian influenza", said Linda Klavinskis, a specialist in immunobiology at King's College London.

"The risk for humans is always a possibility because of the massive shedding of these viruses by infected chicken flocks. However, in my opinion, the chances are very low," she said.

Deadly H5N1 is still found in a handful of countries after a global outbreak that peaked in 2005-2009. On Monday, the Egyptian health ministry said a 19-year-old woman had died of it, the second person known to have died of the disease this year in the country.

In Britain, authorities imposed a restricted zone for 10 km (six miles) around the farm in Yorkshire where bird flu was found and announced all 6,000 ducks there would be destroyed.

In the Netherlands, 150,000 chickens were to be destroyed. The discovery near the village of Hekendorp triggered a three-day ban on shipments of all poultry products out of the country, the world's largest egg exporter. A 10-km exclusion radius imposed around the infected farm will be sealed for 30 days.

The European Union hailed the Dutch and British responses. "We can say that all the protocols were followed and we can only praise the behaviour of the authorities of the two member states," said a European Commission spokesman.

The Dutch government said on Monday that two nearby farms were found to be free of infection.

The Netherlands, with a population of less than 17 million, is the world's second largest exporter of agricultural products after the United States, selling $79 billion euros ($99 billion) of agricultural goods abroad last year. The 700 Dutch poultry farms house 98 million chickens and export 6 billion eggs a year.

All 300 petting zoos in the Netherlands were also closed until Wednesday. "People can spread this flu as well as animals," said the Association of Petting Zoos. "People can't infect other people, but they can infect chickens."

MIGRATING BIRDS SUSPECTED

The H5N8 strain of bird flu was reported in Germany on Nov. 4 on a farm in the northeastern state of Mecklenburg-Vorpommern. The Dutch hens began to show symptoms of H5N8 on Friday and blood tests confirmed the infection on Saturday.

European officials said past outbreaks on the continent had always been brought by migrating birds.

"It is hard to protect farms from wild birds. They are often attracted by food and other birds," the Director General of the World Organisation for Animal Health, Bernard Vallat, told Reuters in an interview.

Elke Reinking, spokeswoman for Germany's state animal disease institute, said links between the type found in Germany and the Netherlands and the one in South Korea were suspected but there was still "no conclusive evidence".

Even short-term restrictions on trade could hit the Dutch agricultural export businesses, with the export of eggs alone worth around 3.2 million euros a day. Between 2003 and 2006, around 30 million hens were culled in the Netherlands after an outbreak of another bird flu strain, H5N7.