Indonesia confirmed on Wednesday its first deaths from bird flu, saying tests on a father and his two young daughters who died recently showed they had the virus.

Avian influenza, which arrived in Asia in late 2003, has so far killed 40 people in Vietnam, half of them since December, 12 in Thailand and four Cambodians.

Health authorities fear the virus will mutate and become easily passed between humans, causing a global pandemic.

“Test results from a Hong Kong laboratory which I received this morning confirmed they were positive for the H5N1 virus,” Indonesian Health Minister Siti Fadillah Supari told reporters.

Asked if the three died from bird flu, Supari said: “Yes.”

“It is not yet known how they got infected, but we continue to conduct an investigation on the ground,” she said.

“The results show (the virus is) a conventional one, and not a new virus. Therefore, there is no need to worry about human-to-human transmission.”

Authorities have taken samples of more than 300 people who had contact with the family on the outskirts of Jakarta.

They also plan to carry out extensive tests on animals within a 20-km (12-mile) radius of the family’s house and slaughter those infected.

World Health Organisation representative Georg Petersen told British Broadcasting Corporation that an in-depth investigation was needed, adding that in other countries the source of infection was often not known straight away.

However, chicken sellers and residents in Jakarta appeared unconcerned.

“I heard about bird flu. It doesn’t affect our sales. Moreover we have a shortage of chicken supply,” said Leo, a vendor in the capital.

Last month, Indonesia reported its first human case in a poultry worker, but the man did not develop symptoms and is healthy.

The agriculture ministry has reported sporadic H5N1 virus outbreaks killing more than nine million fowl in 21 provinces, out of a total of 33, across the archipelago since late 2003.

Indonesian policy favours vaccinating animals rather than culling to stop the spread of bird flu, due to lack of funds to compensate farmers.

The World Health Organisaton has questioned the effectiveness of vaccines and say culling is the best weapon.

The virus has already jumped species in Indonesia and was discovered in pigs in May on densely populated Java island.

Pigs can carry human flu viruses, which can combine with avian viruses, swap genes and create virulent new strains, health experts say.

However, pig farming in Indonesia, the world’s most populous Muslim country, is not widespread. Islam regards pigs as unclean animals.