U.s. Fish And Wildlife Service  /  AP file
Brian McCaffery, a biologist with the U.S. Fish and Wildlife Service, conducts shore bird research inside the Yukon Delta National Wildlife Refuge in southwest Alaska. The spring migration of birds from Asia to Alaska is expected to start soon, and this year it will encounter a beefed-up federal effort to monitor for bird flu.
updated 4/20/2006 4:37:27 PM ET 2006-04-20T20:37:27

Ducks have a flu season just like people do — and they’re more likely to be sick in the fall than in the spring.

So authorities must keep their guard up even if the government’s mass testing of migrating birds, beginning now in Alaska, doesn’t spot the worrisome H5N1 bird-flu strain right away.

That’s a key warning from a new review, being published Friday, of what scientists know — and don’t know — about how waterfowl constantly incubate influenza, and how much of a role wild birds play as this deadly new flu strain hopscotches around the globe.

And it’s one that federal wildlife officials are taking into account as they determine how many birds to test now, as ducks and other migratory species start flying into Alaska’s breeding grounds from Asia, and how many to test later in the year.

“If results in the spring are entirely negative, we still have that opportunity in the late summer and the fall when many species of birds come into closer contact with one another ... all using the same wetlands at the same time rather than using more discreet breeding areas,” said Grace McLaughlin, who is helping to lead that testing at the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis.

'We must err on the side of caution'
Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, agreed on Thursday that avian flu has shown a seasonality in poultry, but she added, “We don’t know if it will back off this summer.”

“Obviously, it’s a pandemic if you’re a bird, but its certainly not a pandemic if you’re a person,” she said. Nevertheless, “we must err on the side of caution” by preparing for this disease, she told a meeting of the American Association for the Advancement of Science.

Among other research, she said, her agency is planning a study this fall of how non-drug measures such as masks affect the spread of seasonal influenza, information they hope will also be useful if bird flu occurs here.

The virulent H5N1 strain erupted in Asia and has now spread to Europe and Africa, killing or causing the slaughter of more than 200 million animals — and killing 110 people who had close contact with sick birds — since 2003. Health authorities worry that eventually this virus could become easily spread person-to-person, sparking a global epidemic.

Virus expected to make landfall soon
For birds, H5N1 already is an epidemic in much of the world, and authorities fear it could finally reach birds in North America sometime this year.

H5N1 is most lethal to poultry, and outbreaks originated from chickens in China, not from wild birds, said Ron A.M. Fouchier, a virologist at the Netherlands’ Erasmus Medical Center who led the scientific review published in Friday’s edition of the journal Science.

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Facts not fearsThe question is what role wild birds now play as the virus hops across continents. There’s growing suspicion that international smuggling of contaminated live poultry or poultry products, such as fertilizer, may be playing a bigger role.

But wild birds do play some role, Fouchier said, pointing to dead swans found in parts of Europe where no chickens were sick. What isn’t clear is whether the swans were sentinel species, the victims that died after infection from a still unknown source, or were actual flu spreaders.

In Europe last fall, scientists spent three months testing 30,000 live wild birds and couldn’t find the virulent H5N1 strain — but they did find it in 500 of 2,000 dead birds tested, Fouchier said in calling for better global surveillance to quantify and understand flu strains in birds.

The U.S.-based Wildlife Conservation Society, with some government funding, is about to launch a global bird-testing network to help do that, said William Karesh, chief of the nonprofit group’s field veterinary program.

Global patterns of infection
Meanwhile, as the U.S. steps up its effort to detect H5N1’s arrival, Fouchier’s review does provide some reassurance, McLaughlin noted: Over the years, there hasn’t been much mixing of Eurasian and North American strains of bird flu.

Nor do very many species fly from Asia into Alaska.

But, “the chance is certainly not zero,” Fouchier said. “In America, you cannot simply rely on the geographical separation of the continents.”

Fouchier and colleagues in Sweden painstakingly detailed global patterns of flu infections among wild birds, an analysis that suggests that climate and migratory patterns coincide to spur spread.

Flu viruses like cold weather, and cold water — ducks and other birds typically trade influenza through feces in ponds or lakes. Flu viruses can live more than 30 days in near-freezing water but for no more than four days in warm water. Migrating ducks in turn tend to have the most flu infection when young, immune-naive birds are congregating in early fall, to prepare for winter flight to warmer climates.

“This is not the time of year you’d expect it to come in force,” agreed Rob Fergus, science coordinator for the National Audubon Society.

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