Thailand said tonight 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 World Health Organization (WHO) said there was no evidence yet the bug had mutated into a feared strain easily transmitted by humans.
The Thai government said a 26-year-old woman who died on September 20th 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.
The WHO and the US Centers for Disease Control and Prevention had been part of the investigation of the case from the start and agreed it "would not pose a significant public health risk," the statement said.
International health officials have been on alert for signs that H5N1, the avian flu hitting parts of Asia and which is normally transmitted by birds, can jump the species barrier and evolve into a potentially devastating human virus and spark a pandemic like one in 1918 which killed 20 million people.
The head of the WHO's global influenza program, Dr Klaus Stohr, said in Geneva there were no signs yet the Thai case was the feared signal a human epidemic could be on the way.