Alaskan Ducks Tested for Bird Flu

Stefan Lovgren
for National Geographic News

September 13, 2005

Since late 2003, tens of millions of chickens have either died or been slaughtered in East and Southeast Asia in an attempt to contain the spread of a deadly strain of the avian flu virus.

But there is another possible carrier of the virus far more difficult to control than domesticated chickens: migratory birds.

Migrating birds may have caused the outbreak of avian flu that killed thousands of domestic fowl in Siberia this summer. Scientists have also found birds on Lake Qinghai in China, where many birds come to migrate, to be infected with the strain.

Fearing that the virus may be spreading from Asia to other parts of the world, bird experts in Alaska have in recent weeks been testing migratory birds there for avian influenza.

If avian flu is introduced to North America by migrating birds, "Alaska is the most likely state where it would first arrive, because that's where the … flyways intersect," said Hon Ip, director of the U.S. Geological Survey's (USGS) virology lab in Madison, Wisconsin. His lab is handling some of the tests.

Highway or Flyway?

There are several avian flu strains. The most dangerous is the HPAI H5N1 strain, which first appeared in Asia in 1997 and since 2003 has caused mass mortality in chickens.

Although the strain does not spread easily to humans, more than a hundred people have been infected with the virus. At least 55 people have died.

Scientists worry that H5N1 will combine with a human flu virus strain to create an exceptionally dangerous influenza that could spread easily from person to person and potentially kill millions of people.

Migratory waterfowl—particularly wild ducks—are the natural reservoir of avian influenza viruses. The birds typically do not become ill when infected with the virus. Domestic poultry, on the other hand, are highly susceptible to epidemics of avian flu viruses.

Ip notes that some bird flu epidemics arose after domestic bird flocks came in contact with wild migratory waterfowl. The USGS virologist adds that scientists suspect that H5N1 first arose in the poultry industry in China and that "movement of chickens and poultry workers contributed to spread the virus in the region."

"The $64,000 question is whether the spread [of avian flu] is by the highway or the flyway," he said.

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.

Northern Pintails

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 roulette—time is not on our side."

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