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Evidence Suggests Link Between Migration, Bird Flu

MICHELE NORRIS, host:

To keep bird flu from spreading, Europe has announced a continentwide effort to keep chickens and other domestic fowl separated from wild birds. That's because there's growing evidence that migrating birds have moved the virus across Asia and into Europe. NPR's John Nielsen explains.

JOHN NIELSEN reporting:

When the killer version of the bird flu virus started spreading through Asia two years ago, scientists started arguing about how this virus moved from place to place. Hon Ip, a virologist with the National Wildlife Health Center in Madison, Wisconsin, says the basic question sounded simple.

Mr. HON IP (National Wildlife Health Center): Is the H5N1 being carried to these outbreaks by something with wings or by something with wheels?

NIELSEN: In other words, did this virus spread as poultry trucks drove to markets, or were wild birds that landed near chicken farms carrying the virus off to new locations? William Karesh, a bird flu expert with the Wildlife Conservation Society, says he used to be virtually certain that wild birds were not involved.

Mr. WILLIAM KARESH (Wildlife Conservation Society): Because when this H5N1 gets into wild birds, they tend to die.

NIELSEN: `Dead birds do not migrate well,' he used to add. And for a time that was that. But then last May, Karesh and Ip began hearing things that made them reconsider their position. First, in May, there came a strange report from an isolated lake in Qinghai, China. Thousands of bar-headed geese and other waterfowl had started staggering around like drunks and then falling over dead. The cause of death in every case was the bird flu.

Mr. IP: And what ultimately happened was we think that between a thousand to up to 5,000, depending on whose number you believe, bar-headed geese died during this H5N1 outbreak.

NIELSEN: Ip says there weren't many poultry farms or truck routes in the area, and it was a major stopover for migrating birds. In his opinion, that meant one thing.

Mr. IP: Birds brought the virus to the park and then caused an outbreak in the park.

NIELSEN: A few months later another avian flu die-off was reported in Mongolia. When it happened, William Karesh flew in from New York to test thousands of healthy birds. He was hoping to find a species that was capable of carrying this virus without being killed by it. All of the tests came up negative, but in the process Karesh came up with an idea: Maybe the victims moved the virus forward before they died.

Mr. KARESH: Maybe they can fly for a few days before they get sick. So maybe they get infected and can make it a hundred miles, land in another lake; they get sick, but maybe they infect some more birds, who go another 2 or 300 miles. It's like a leapfrog effect.

NIELSEN: The die-off in Mongolia also took place in the middle of a migratory pathway. It funnels birds flying south for the winter toward a massive set of wetlands at the mouth of the Danube River in the Black Sea. If migrating birds were, indeed, carrying this virus, this is where the avian flu would turn up next, and now it has. Recently the H5N1 was found in Turkish poultry and possibly in Romanian waterfowl. Michael Perdue, an influenza expert with the World Health Organization, adds that the virus looks familiar.

Mr. MICHAEL PERDUE (World Health Organization): The virus in Turkey is probably the same virus as what we saw in Qinghai, China, which is 4,000 miles away from the Turkey outbreak. So it's looking more and more like the only mechanism that we could move this virus around is through the migratory waterfowl pathways.

NIELSEN: In the wake of these findings, scientists are stepping up efforts to catch this virus on the wings of migrating birds. So far there's no evidence that it's moving along other migratory pathways, including one that brings Asian waterfowl into the United States through Alaska. John Nielsen, NPR News, Washington. Transcript provided by NPR, Copyright NPR.

John Nielsen
John Nielsen covers environmental issues for NPR. His reports air regularly on NPR's award-winning news magazines, All Things Considered, Morning Edition and Weekend Edition. He also prepares documentaries for the NPR/National Geographic Radio Expeditions series, which is heard regularly on Morning Edition. Nielsen also occasionally serves as the substitute host for several NPR News programs.