Senior health officials from the United Nations and the United States are warning that the world community must prepare for the possibility that a virulent strain of bird flu could mutate into a form that could infect large numbers of people. The officials issued the warning in Thailand, as they began a trip to several Southeast Asian nations hit by the virus.

Jong Woo Lee (file photo)

World Health Organization Director-General Jong Woo Lee says avian influenza, known as bird flu, is already endemic in Asia. "The burning question is will there be a human influenza pandemic? I believe, on behalf of WHO, I can tell you there will be," he said.

Health officials fear that a pandemic will occur if a recent strain of the virus, which has killed one-half of the humans it has infected, mutates into a form that can be transmitted between people. The virus has only infected humans who came into contact with contaminated birds.

The strain (called H5N1) has killed 60 people in four Southeast Asian nations, and led to the culling of 140 million birds. The strain has been found in 10 Asian countries, and, carried by migrating wild birds, has recently spread to Russia, Romania, and Turkey.

The head of the delegation, U.S. Health Secretary Michael Leavitt, said this strain of flu is similar to the strain that killed more than 20 million people in 1918.

"The doctrine of the United States in dealing with pandemic flu is that, if it happens anywhere, there is risk everywhere, and that we must form a network of collaboration to deal with it," said Mr. Leavitt.

The U.S. and Thai governments are calling for international participation in a partnership pursuing several lines of defense - containment of outbreaks among poultry stocks, surveillance, so that they do not spread, and regional stockpiles of vaccines and anti-viral drugs to fight outbreaks among humans.

The Thai government announced that it has 700,000 capsules of flu vaccine, and will contribute five-percent of these to a regional stockpile.

But the health officials noted that stocks and manufacturing capacity for the only known bird flu drug (Oseltamivir, known as Tamilflu) are well below those needed in a pandemic. They also say that governments must not hide outbreaks, but share information so that new strains of the virus can be identified, and better containment measures launched.

After Thailand, the delegation is to visit Cambodia, Laos, Vietnam and Indonesia.