rge scale global outbreak of bird flu can occur any time given the current conditions, a Chinese scientist has warned. "It's bird flu that renders the current situation so serious," said Zhong Nanshan, an academician of the Chinese Academy of Engineering. He said a mutated flu virus might present a more dangerous threat, Prensa Latina news agency reported.

Bird Flu or avian influenza has infected more than 100 people in Asia and killed about half of them since 2004, three health agencies, including the World Health Organisation, said last month.

"But we can't pin down a specific time for the outbreak so far," Zhong, told the Information Time.

He said a global flu outbreak generally took place every 20 to 50 years and the last such epidemic had occurred more than 20 years back.

"Till date, we still can't tell whether bird flu viruses can join human flu viruses to create some viruses that could live inside humans," he said.

He recommended, especially the aged, children, patients and medical workers, who have proved to be particularly vulnerable to infection, should get inoculation during the September-October period, the time immediately before flu outbreak season.

More than 140 million chickens have been slaughtered in South East Asia because of concern that H5N1, a deadly strain of the virus, may mutate into a form easily transmissible between humans.

Of the 15 avian influenza viruses, the H5N1 mutates rapidly and can acquire genes from viruses infecting other animal species, according to the WHO website.