Recent outbreaks of avian flu in Kazakhstan, Mongolia, and southwestern Siberia in Russia have been attributed to H5N1. The incidents mark the first time the virus has extended into the regions, though there is no confirmation that migratory birds brought the disease there.
But a study of birds found sick or dying on China's Lake Qinghai last spring showed that they carried H5N1. The lake is a breeding center for migrant birds from Australia to Siberia.
"A lot of waterfowls will come to the lake and mix together," said George Gao, a biologist at the Chinese Academy of Sciences in Beijing, who conducted the study. "This might help spread the virus once [the healthy birds] fly out again."
Birds that are not sickened by the virus pose the biggest threat for its spread. If the virus kills a bird quickly, the animal is less likely to spread the disease.
"These birds easily spread the virus, because they can still fly," said Michael Lai, a virologist at the University of Southern California in Los Angeles and the Academia Sinica in Taiwan.
Some avian flu viruses have in the past made their way from Europe and Asia into North America.
"It does not occur very frequently," said Ip, of the USGS. "But it has happened, and it will happen again in the future."
The avian flu surveys underway in Alaska have been piggybacked on already scheduled efforts to examine certain bird species, band them, and track their movements before hunting season.
Working at several Alaskan sites, bird experts have collected samples from geese and ducks by taking swabs from the birds' tailpipes to see if the birds are carrying the virus in their feces.
Among the target species is the Northern pintail, a migratory duck common in Alaska. Some Alaskan pintails are known to summer in Russia.
"If there is transmission of avian flu going on among the wild population of birds, pintails could potentially become infected and bring the virus to North America," said Russ Oates, the chief of the waterfowl branch at the U.S. Fish and Wildlife Service in Anchorage.
So far, there is no evidence of avian flu in North America. But Ip worries that it might just be a matter of time before the disease spreads out of Asia.
"The longer the virus persists in poultry, the greater the chance that, at some point, it will spread to species of wild birds that can carry the virus to new areas," the USGS virologist said. "It is like playing Russian roulettetime is not on our side."
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