Hanoi, Feb. 4 (Reuters): The death toll from Asia’s bird flu outbreak rose to 15 today as the virus ravaged poultry flocks in 10 countries and, most worrying, spread in China.

Vietnam said a 17-year-old woman had died of the disease and Thailand said tests confirmed a six-year-old boy who died earlier in the week was infected with the H5N1 virus.

The H5N1 bug, which can cross the species barrier, is still spreading despite a mass slaughter of poultry the UN’s Food and Agriculture Organisation says it estimates at 50 million birds.

Guangdong, the southern Chinese province from which the Sars virus emerged before affecting 30 countries last year and killing nearly 800 people, definitely has the H5N1 avian virus.

Now 12 of the vast country’s 31 provinces have confirmed or suspected outbreaks of bird flu. The FAO said bird flu had been confirmed in 53 of Vietnam’s 64 provinces. China has yet to report any human infections, unlike badly hit Thailand with 17 suspected cases as well as five confirmed and two probable deaths from the disease.

Most of the deaths have been attributed to direct contact with infected fowl, like the Thai boy who was present when his grandfather killed chickens.

But Guangdong, where people live cheek by jowl with poultry and other farm animals, is widely regarded as a breeding ground for viruses which could cause a pandemic in humans.

That is still regarded as a remote threat and the WHO said the possibility that two Vietnamese sisters might have caught bird flu from their brother did not mean a pandemic was any nearer. But, WHO spokesman Peter Cordingley said, the battle against bird flu was not being won.

“We are looking at a very serious situation in terms of the virus in the poultry world,” he told Reuters Television in Manila. “At the moment, we are losing more than we are winning.”

The FAO also said in a statement a smaller outbreak in Laos, sandwiched between China, Vietnam and Thailand, had not been stopped despite cullings on 20 farms. Thailand is one country which believes it is winning the fight. Its “red zones”, the 5-km area around a confirmed outbreak within which the government orders the slaughter of all poultry, were down to just 14 in seven provinces.