Asian countries and regions that have so far escaped the bird flu spreading across the continent stepped up measures Thursday to keep the virus outside their borders.

Hong Kong isolated a woman who returned from Viet Nam with suspicious pneumonia symptom. Singapore intensified a campaign to slaughter crows, scavengers considered potential spreaders of the disease because they could contract the virus from dead birds.

Singapore and Hong Kong were hit hard by severe acute respirtory syndrome last year and both were on high alert to prevent an outbreak of bird flu, which has killed 10 people in recent weeks.

Tens of millions of chickens and ducks have died in 10 countries across the region -- from the disease or in government-ordered slaughters. The virus has jumped to humans in Viet Nam, where eight people have died, and in Thailand, where two have died.

Indonesia ordered all chickens in affected areas killed, reversing its earlier insistence that a wholesale slaughter was not necessary. And Thailand, which for weeks claimed to be bird-flu free, said the disease was spreading rapidly across its countryside.

The World Health Organization warned that the unsafe culling of poultry in Asia is increasing the risk that the bird flu outbreak could take root in humans.

Television and newspaper images of bare-handed people, without goggles or masks, flinging chicken carcasses into mass graves or stuffing live ones into sacks have alarmed officials at the UN health agency.

"They are trying to eliminate the animal reservoir, which is what we want, but if they are exposing themselves to the virus while they're doing that it might defeat the purpose,'' said Maria Cheng, a spokeswoman for WHO's infectious diseases unit.

Scientists say it is especially important to wear protective gear during slaughter as the birds tend to excrete more virus when they are under stress.

The danger is that somebody could become infected with the bird flu virus while already carrying a human variety of influenza.

The two flu viruses could then swap genes, resulting in a hybrid with the virulence of the bird flu and the contagiousness of human flu, triggering the next global flu pandemic.

WHO acknowledged that the problem is probably due to a lack of resources in many of the areas, and the agency has appealed to richer countries to step in with money and technical expertise.

In China, health authorities banned the slaughter of poultry in Beijing, a city of 13 million people, but stepped up chicken slaughters elsewhere.

China said it intends to kill all livestock birds within a two-mile radius of infected sites. It also banned poultry exports from three regions and disinfected cars around a southern town where the virus was found in ducks.

Fears that infected people could travel, spreading the virus across borders as happened with SARS, prompted Hong Kong authorities to isolate a 75-year-old woman, sick with flu-like symptoms, after she returned from hard-hit Viet Nam.

Tests to determine whether she had bird flu came up negative Thursday, but the woman was still being tested for SARS, Hong Kong's Hospital Authority said.

China's Taiwan Province ordered the slaughter of some 50,000 poultry with a mild strain of virus that officials say doesn't infect humans.

Singapore, where no cases of bird flu have been reported to date, boosted its long-running crow culling campaign as a precaution.

Bird flu is believed to be spread by migratory ducks and other wild birds. Most human cases have been traced to direct contact with sick birds and many victims have been young children.

Officials have said there are no indications so far that bird flu is spreading to people who eat properly cleaned and cooked poultry products, but governments worldwide have slapped import bans on poultry from countries affected with bird flu.

The European Union expanded its ban on Thursday to include imports of pet birds from affected countries.

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