Survival of hosts has avian flu scientists worried

And the bad news is getting worse.

What has scientists newly worried is not the fact that the avian flu virus H5N1 already has killed at least 60 people overseas. Or that it has spread from Southeast Asia to China and Russia.

What has them convinced about the diminishing odds of escaping a worldwide health catastrophe -- one study estimates that fatalities in the United States could surpass half a million -- is that wild birds overseas no longer seem to be dying.

That means the virus is mutating, and scientists fear it has now adapted so that it can survive the annual migration of wild birds from Asia to North America without killing its hosts.

"That's a real danger sign," said veterinarian Carol Cardona of the University of California Davis.

Cardona is part of the growing army of scientists and health-care professionals gearing up to fight what could become the first flu pandemic since 1918, when a Spanish flu virus -- also believed to have been spread by birds -- killed between 20 million and 40 million people around the world.

More Americans died in that outbreak than were killed in World War I. And already the projections are that the next pandemic, perhaps just months away, will kill similar numbers of people.

So far, the virus has not mutated or combined with other influenza viruses so that it can spread from human to human.

"Most experts believe it is not a question of if, but when," said David Daigle of the Centers for Disease Control and Prevention in Atlanta.

According to a recent report by the Trust for America's Health, the U.S. toll could top 540,000.

While scientists and health officials stress that there is no evidence of an Asian variety of the H5N1 virus in the United States now, it could arrive at any time with passengers unloading from an overseas flight from Thailand, China or Russia.

Or it could arrive on the wings of an infected bird.

Cardona, who also is a spokeswoman for the Department of Homeland Security's National Center for Animal and Zoonotic Disease Defense at UC Davis, is helping oversee in California a national effort to detect the virus's avian arrival.

This year, she said, some 2,000 nonmigratory wild birds will be checked to see if they have any signs of the Asian H5N1 virus. The nonmigratory birds are easier to locate and swab, she said, and they are likely to pick up the disease from waterfowl and other birds migrating south from Alaska on the Pacific Flyway.

In Alaska, veterinarian Jonathan Runstadler is overseeing state-funded research doing a similar thing to migratory birds that have flown from Asia to their summer nesting grounds.

Runstadler said they hope to swab 5,000 birds before the fall migration begins in a matter of weeks.

The concern is that migratory birds from Asia, already in Alaska, will mix with other birds soon to be headed south to the mainland United States. Because ducks and geese carry other flu viruses that already have made the leap to human-to-human transmission, the concern is that the deadly H5N1 strain will combine with one of them to produce the killer bug.

"This may be the place where new viruses are created," said Runstadler, an assistant professor at the University of Alaska's Institute for Arctic Biology.

In California, the goal is to keep the virus from poultry farms in the Central Valley and southern part of the state before they become incubators or, worse yet, breeding grounds for a deadly form that can be transmitted from human to human.

"We all believe that wild birds are not likely to cause a pandemic without an intermediate host for the virus," Cardona said. "And poultry are likely to be that host."

Already, she said, poultry growers and backyard farmers are being urged to keep the water and feed for their chickens and ducks protected from wild birds so that the virus can't be passed along.

The deadly strain of the H5N1 virus was first detected in Southeast Asia more than two years ago. Tens of millions of domestic ducks and chickens have been slaughtered and burned to stop its spread, but the virus quickly migrated to China and then Russia and now other countries as well, carried by wild birds.

More than 60 people who have come into contact with sick birds have died.

While there have been no reports of the virus being transmitted between people, British researchers reported finding the H5N1 virus in the spinal fluid of a young Vietnamese boy earlier this year, indicating that the virus is mutating to the point it can infect the human brain.

Researchers working on an anti-viral drug to fight the virus have been surprised by its accelerating mutation.

Recently there have been reports from the National Institutes of Health that a drug known commercially as Tami-flu has shown promise in studies involving rats that it could suppress the spread of the virus.

"That's very encouraging," said Ken August, spokesman of the California Department of Health Services. "But to produce enough for all Americans and then to distribute it to all who need it would be an enormous challenge."