HANOI, Vietnam -- After days of denying it had a problem, Thailand became the latest flashpoint in the bird flu crisis Thursday with claims that a village boy is infected. The World Health Organization warned the virus could mutate into a form deadlier to humans.
Bird flu has killed five people in Vietnam and infected millions of chickens across Asia. Together with the re-emergence of severe acute respiratory syndrome, the fast-spreading virus has put Asia on a region-wide health alert.
A WHO team and six scientists from the U.S. Centers for Disease Control are in Hanoi hoping to track down exactly how the H5N1 virus has jumped from poultry to people.
Scientists believe people get the disease through contact with sick birds. So far, there has been no evidence of person-to-person transmission.
But health officials worry that the avian virus could mutate to allow human transmission, which could make the disease a bigger health crisis than SARS. That disease, also a virus, killed nearly 800 people worldwide last year.
"The more widespread it becomes, the greater the possibility that the (bird flu) virus could become altered and become more of a threat to the human population," said WHO spokesman Bob Dietz.
In Bangkok, Thai Prime Minister Thaksin Shinawatra denied claims that the country's first bird flu case in humans had been confirmed by a laboratory.
A Thai senator, Nirun Phitakwatchara, accused officials of covering up "for political and business reasons" the case of a boy in central Suphanburi province, whom he said tested positive for the disease. The child is one of three people being tested for bird flu in Thailand.
The country is among the world's top five poultry exporters and stocks in its multibillion-dollar industry plunged as much as 7.1 percent on its stock exchange.
Thailand insists it has not been hit by bird flu, which has attacked millions of chickens in Vietnam, Japan and South Korea. However Japan announced a ban on Thai chicken meat imports Thursday as a precaution.
Fears over Asia's bird flu outbreak grew when worst-hit Vietnam admitted Wednesday that nearly 900,000 chickens possibly exposed to the deadly virus had been sold to the public.
The chickens, which came from the two hardest-hit southern provinces, were sold on the market in early January before the country ordered a mass cull, a senior veterinary official said.
Jittery governments struggled with ways to contain the disease. Several countries have banned poultry imports from Vietnam, South Korea and Japan. Mainland China, which is battling a resurgence of SARS, has been especially vigilant at its southern borders with Vietnam.
In Hong Kong, a dead falcon tested positive for bird flu Wednesday, prompting officials to step up surveillance there.
It is the first such bird flu epidemic in Japan since 1925, and the first ever documented in Vietnam and South Korea.
The deadly H5N1 virus crossed over from chickens to humans in Hong Kong in 1997 and killed six people.
International health experts have started work on a human vaccine but expect it will be months before one is ready.