Thailand said Tuesday it had found its first known probable case of a human being infecting another with bird flu, but insisted it was an isolated incident that posed little risk to the greater population. 

The government said a 26-year-old woman who died on September 20 could have caught the H5N1 virus in the village where her daughter lived but probably was infected by the 11-year-old girl while looking after her in hospital. "It would have been due to close and prolonged face-to-face exposure," the government statement said.

The World Health Organization and the US Centers for Disease Control and Prevention have been part of the investigation of the case from the beginning and agreed it "would not pose a significant public health risk," the statement said.

The mother's death took to 10 the number of Thais killed by the H5N1 virus. In Viet Nam, 20 people have died of the disease.

Experts have long feared the H5N1 bird flu virus, which swept through much of Asia early this year, could mutate into a form that could be passed from person to person and set off a pandemic like the one in 1918, which killed 20 million people.

But, they say, the H5N1 virus would have to go through an animal -- most likely a pig, although cats can also contract it -- capable of harboring the human influenza virus with which it could merge to forge a virus that could trigger a pandemic.

The experts agreed "there is no evidence to suggest that the virus has mutated," the statement said.

"This could be just a dead end. That's what it looks like now. But we really need to finish the studies we have ongoing. We'll know more this week," WHO spokesman said.

Thai Prime Minister Thaksin Shinawatra called an emergency meeting of provincial governors today to beef up measures against the disease.

(China Daily September 29, 2004)