BF strain could be hard to spot in migratory birds

    Deadly bird flu strain could be hard to spot in migratory birds


Posted: 04/20/2006 07:00:31

WASHINGTON (AP) -- Ducks have a flu season just like people do -- and they're unlikely to be sick 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 allocate 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.

"Even if we don't have any significant die-off during that breeding season, there is the possibility that when birds really start congregating to prepare for (winter) migration and start migrating, that we could see some outbreaks," said Grace McLaughlin, who is helping to lead that testing at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis.

The virulent H5N1 strain has 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.

But it's already an epidemic for birds everywhere except the Western Hemisphere. Authorities fear it could afflict 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.

The question is what role wild birds now play as the virus hops across continents. There's growing suspicion that international smuggling of contaminated poultry and poultry products may be playing a bigger role.

But wild birds do play some role, Fouchier said, pointing to the rash of 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 spreaders of it.

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 do just that, said William Karesh, chief of the nonprofit group's field veterinary program.

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.

Fouchier and colleagues in Sweden painstakingly detailed global patterns of flu infections among wild birds, an analysis that suggests that climate and migratory patterns must 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. Ducks in turn tend to have the most flu infection when young, immune-naive birds are congregating in early fall, to prepare for winter migration 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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