BANGKOK (AFP) - The World Health Organization said it suspected bird flu had passed from human to human in northern Thailand, marking what could be the first such transmission of the lethal virus.
"From the existing data ... we are suspecting human-to-human transmission" of bird flu, the WHO's acting Thailand representative Kumara Rai told AFP after studying information from Kamphaeng Phet province where a girl and boy are suspected to have died from the virus.
The 11-year-old girl's mother, who lived near Bangkok but traveled north to visit her daughter in hospital and then attend her funeral, returned to the Thai capital where she too fell ill and died. Her death is also on the suspect list.
Laboratory tests on the three fatalities, as well as on the girl's aunt who is hospitalised with severe pneumonia, were being conducted to detect the virus that has already killed 28 people in Asia since last December.
Health Minister Sudarat Keyuraphan said Thailand has been put on full alert as a precautionary measure but quickly sought to downplay the fears, stressing preliminary test results from the aunt showed no bird flu.
"Initial test results (from the aunt) were negative, so at the moment it's a relief for the ministry concerning whether the virus has jumped from human to human or not," Sudarat told AFP. "But we still need to double check a final test."
However, Rai said the WHO was still "very much concerned, but we are awaiting the laboratory confirmation", which is expected as early as Monday.
Health ministry officials have confirmed the girl and the 13-year-old boy in Kamphaeng Phet had come into contact with sick households' chickens, but Rai and others have said it was not clear whether the mother and the aunt had contact with the birds.
Rai met Friday with field epidemiologists, Thai-based officials from the US Centers for Disease Control and senior Thai health ministry officials to establish whether the women had come into contact with the fowl.
"We are still almost firm that there was no contacts with sick birds," Rai said.
Charal Trinvuthipong, director general of the disease control department, said in a Thai daily he was concerned that the women may have caught the virus directly from the girl because the mother identified as Pranee and the aunt, Pranom, had "no history of direct contact with chickens".
"If we find the virus in Pranom, and both Pranom and Pranee had no direct contact with the chickens and merely tended to their sick girl, it could mean that the virus jumped from human to human," Matichon newspaper quoted him as saying.
Charal said the aunt's condition had stabilised but her six-year-old son was hospitalised with fever and pneumonia and was now listed as the kingdom's fifth suspected bird flu case.
Several people have been placed on Thailand's suspect list in recent months but nearly all of them have since been cleared.
Rai said he had contacted the UN health agency's headquarters in Geneva to urge them to send experts to Thailand to assist in the investigation.
Avian influenza's lethal H5N1 strain has killed 19 people in Vietnam and nine in Thailand in the past 10 months in two waves of Asian outbreaks which also caused the deaths or culling of more than 100 million chickens.
The WHO fears H5N1 could mutate into a highly contagious form and trigger a global human flu pandemic.
When asked if a confirmed viral leap between humans in the Thai cases would mark the first step in such a feared mutation, Rai said, "I think so."
The WHO suspected human-to-human transmission of bird flu once before in Vietnam during the height of the first wave of outbreaks in February, but was proven wrong, Rai said.
"Hopefully the same holds true for this outbreak."
Since the second wave of bird flu began in early July, Thai authorities have confirmed 149 outbreaks in 30 provinces.
Thai Prime Minister Thaksin Shinawatra on Saturday lashed out at government agencies for failing to contain the new outbreaks.
"I have instructed the public health and agriculture ministers to supervise the tackling of bird flu and the focus on human safety. They have failed to report when poultry is dying," he said in his weekly radio address.