A virulent Asian strain of bird flu has arrived in Croatia for the first time and may also have infected three tourists who visited Thailand, officials said, deepening worldwide concern over the spreading virus.

A virulent Asian strain of bird flu has arrived in Croatia for the first time and may also have infected three tourists who visited Thailand, officials said, deepening worldwide concern over the spreading virus.

Dead swans found last week in Croatia's rural northeast were carrying the H5N1 strain that has killed at least 62 people in Asia in the past two years, a veterinary official said, while thousands of miles away on the French Indian Ocean island of Reunion three humans were being tested for bird flu.

The results of tests carried out by a British laboratory on the Croatian material were "what we were expecting", veterinary official Vladimir Savic told a news conference. "It is the highly pathogenic H5N1."

Europe is on maximum alert for the further spread of the H5N1 strain, which has already also been detected in Romania, Russia and Turkey, a westward sweep health experts believe is caused by birds migrating ahead of the winter.

Nearly all the humans who have thus far died from the H5N1 virus -- two thirds of whom were in Vietnam -- had been in close recent contact with infected birds.

France revealed Wednesday that three people from Reunion were feared to have been infected with the disease during a trip to Thailand.

Officials suspected the trio may have caught H5N1 when they visited a Thai zoo together and were in contact with birds there, French Health Minister Xavier Bertrand said in Paris.

Initial tests carried out after their return to Reunion, a French-ruled island in the middle of the Indian Ocean, had been positive, and samples were being rushed to Paris for further tests, he said.

"We will have results for the first patient tomorrow," said Bertrand. "For the moment these are only suspicions. Nothing has been confirmed," he said.

Though the virus spreads quickly between birds, it does not pass easily between humans.

The big fear is that it could mutate with a form of human flu to create a strain capable of jumping from human to human and unleashing a pandemic, which could kill millions worldwide.

Asia has borne the brunt of the disease so far, with China rushing through an emergency response on Wednesday after the country's third confirmed outbreak of the virulent strain inside a week.

Chinese officials mobilized roadside sterilization stations and inspected markets after 545 chickens and ducks died from H5N1 in the central province of Hunan, the Ministry of Agriculture said in a report filed to the World Organization for Animal Health (OIE).

According to the OIE website, precautionary measures had been taken, including vaccinations and the disinfection of infected areas. The state news agency Xinhua said the outbreak was effectively under control.

Croatian officials said they too had been able to stem the spread of the virus.

"All the measures which we already adopted were justified," Savic told reporters, referring to a precautionary mass slaughter of thousands of chickens and other poultry in the affected areas.

European nations are stepping up defenses against the virus, stockpiling anti-viral agents and preparing crisis measures for a feared pandemic.

The European Union also barred

imports of pet birds following the detection of the H5N1 strain in a dead parrot held in quarantine in Britain.

British officials said the infection -- the first confirmed case within a European Union country -- most likely was spread from other quarantined birds from Taiwan, something Taiwanese officials rejected Wednesday as "unlikely".

Tests on 32 birds which died in British quarantine up to mid-October found that some had an as-yet unspecified strain of bird flu, the British government said. But the full circumstances of the deaths had not yet been established.

The European Food Safety Authority said Wednesday there was no proof people can catch the disease by eating chicken or eggs, but it advised people to properly cook such foodstuff to avoid any risk.

With newspapers around the continent running a spate of sometimes lurid stories about the possible impact of a flu pandemic, many shoppers have begun shunning poultry and eggs, prompting concern from producers and vendors.

"I haven't sold a single egg since Saturday," lamented a stallholder at Zagreb's popular Dolac outdoor market.