An outbreak of bird flu (search) among migratory waterfowl in China suggests the disease — which could trigger a dangerous flu among people — may be poised to spread to India, Australia, New Zealand and eventually Europe, scientists warn.

If the migrating birds carry the H5N1 flu virus (search) beyond its current stronghold in southeast Asia, it could devastate poultry farms and raise the risk of a deadly flu pandemic in people, experts said.

"They're going to spread this ... thing further and further across central Asia and Europe and who knows where," said Robert G. Webster of the St. Jude Children's Research Hospital in Memphis, Tenn., an author of a report released online Wednesday by the journal Nature.

Another report, released by the journal Science, said the finding of the H5N1 infection in migrant birds at Qinghai Lake in western China "indicates that this virus has the potential to be a global threat."

The reports echo concerns voiced last week by the World Health Organization, which urged China to step up its testing of wild geese and gulls. A WHO official estimated that the flu had killed more than 5,000 wild birds in western China.

The outbreak was first detected about two months ago in bar-headed geese at China's remote saltwater lake, which is a key breeding location for migratory birds that overwinter in southeast Asia, Tibet and India. The virus has hit that species the hardest, but also infected d brown-headed gulls and great black-headed gulls.

The H5N1 virus has been entrenched in poultry in southeast Asia since 2003, and variants of it infect people who come in contact with sick chickens. Webster said the Qinghai Lake virus is genetically different from the one that has been infecting people in Vietnam, but it is a "first cousin ... not far away at all." That implies it has the potential for infecting people, probably by way of domestic chickens or ducks, he said.

If a bird flu virus infects a person who also carries a human flu virus, the result could be a hybrid bug that passes easily from person to person. "That's the spark that sets off the forest fire of a global pandemic, and that's what everyone is worried about," said flu expert Dr. William Schaffner of Vanderbilt University.

The flu outbreak in migratory birds at Qinghai Lake "makes us ever more anxious this event could occur" because it suggests the virus could become more widespread, said Schaffner, who was not involved in the new studies.

Both studies discuss the genetic makeup of virus samples from Qinghai Lake and raise concerns about the potential for spreading through migratory birds. The Science report comes from George F. Gao of the Chinese Academy of Sciences in Beijing with colleagues there and elsewhere in China. In lab experiments, they found the virus killed chickens and mice.

The Nature report is presented by Yi Guan of the University of Hong Kong with Chinese colleagues and Webster, who's affiliated with the Joint Influenza Research Center at Shantou University Medical College in Shantou, China.

Webster called the outbreak "a disaster for poultry industries.... Poultry-raising strategies may have to be changed. Vaccines may have to be considered on a wider scale."

He said countries that have invested heavily in clearing the virus from poultry are at risk, presumably even in Europe at some point because of overlapping migratory paths of wild birds.

"If this virus is really in wild migrating birds, and you've cleaned up your country and your domestic poultry industry," he said, "it's going to come back."

Richard Slemons of Ohio State University, who is studying flu in wild birds, said the Qinghai Lake die-off needs to be investigated. But "is this the prelude to something big and disastrous?" he asked. "We don't know."