WASHINGTON, Oct 28 (Reuters) - Migrating waterfowl may be carrying avian influenza viruses from Asia to the Americas, U.S. government researchers reported on Tuesday.

They found genetic evidence that some non-dangerous influenza viruses infecting northern pintail ducks in Alaska are genetically more closely related to Asian strains of bird flu than to North American strains.

"Although some previous research has led to speculation that intercontinental transfer of avian influenza viruses from Asia to North America via wild birds is rare, this study challenges that," said Chris Franson, a research wildlife biologist at the U.S. Geological Survey, who helped lead the study.

USGS and U.S. Fish and Wildlife Service experts have been testing birds in Alaska for any evidence they may be carrying highly pathogenic H5N1 bird flu with them from Asia.

Writing in the journal Molecular Ecology, the USGS team said they had collected samples from more than 1,400 northern pintails from throughout Alaska and compared any viruses they found to virus samples taken from other birds in North America and eastern Asia where northern pintails spend the winter.

None of the samples were found to contain completely Asian-origin viruses and none were highly pathogenic. But certain parts of the genes of the viruses resembled Asian strains, they said.

Since 2003, H5N1 has swept through flocks in Indonesia, Korea, China and elsewhere in Asia, Europe, the Middle East and parts of Africa.

It has killed or forced the slaughter of more than 300 million birds.

Not only is it devastating to the poultry industry but it occasionally infects people and has killed 245 out of the 387 infected people so far, according to the World Health Organization.

Birds can carry dozens of different flu viruses, some dangerous and some not. So far there is no evidence any have carried H5N1 with them to North America from Asia.

(Reporting by Maggie Fox, Editing by Sandra Maler)

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