A newly arrived bird flu is sweeping through wild bird populations in the United States, and that may mean trouble for poultry farmers who have been doing their best to control this flu outbreak in their flocks.

Some 24 million poultry birds like chicken and turkeys have already been lost, either because they died from the virus or were killed to prevent its spread. But unlike a similar bird flu outbreak seven years ago, this one is unlikely to just burn itself out.

That's because this particular flu virus seems capable of hanging around in populations of wild birds, which can pass the virus on to poultry farms. While chickens and turkeys with the virus quickly sicken and die, some waterfowl can remain healthy with the virus and carry it long distances.

Scientists believe that wild migratory birds brought this virus to North America a few months ago. Since then, more than 40 wild bird species in more than 30 states have tested positive. This strain of bird flu virus has turned up in everything from crows to pelicans to bald eagles.

"It's somewhat surprising how widespread it is already in North America," says Jonathan Runstadler, an influenza researcher at Tufts University. "It's clearly able to persist and transmit from year to year in parts of Asia, Europe, Africa, and I don't think we should be surprised if that's going to be the case here."

As the virus moves across the country, and potentially settles in for the long haul, it will encounter new animal species that could get infected. This pathogen will also get a chance to genetically mingle with the flu viruses that are already circulating in the U.S.

"What that means for the virus in terms of how it evolves, how it changes, we just don't really know," says Richard Webby, a flu researcher at St. Jude Children's Research Hospital.

There has been only one known human case

So far, the risk to humans seems low.

But since related bird flu viruses have repeatedly jumped into people in the past, public health experts are watching for any signs of genetic changes that could make the virus able to move into humans.

"We're concerned with any avian influenza virus that's circulating in domestic poultry or wild birds," says Todd Davis, an expert on animal-to-human diseases at the Centers for Disease Control and Prevention (CDC). "Because humans have no prior immunity to these viruses typically, if they were to be infected and spread the virus to other humans, then we could have another pandemic virus on our hands."

This virus doesn't have genetic features previously associated with related bird flus that have infected humans. And the only person known to have contracted this particular bird flu virus was an elderly person in the United Kingdom who lived in close quarters with ducks; while some of the ducks got sick and died, their owner never had any symptoms.

The CDC has been monitoring the health of more than 500 people in 25 states who were exposed to infected birds, says Davis. Although a few dozen people did develop flu-like symptoms, all were tested and none were positive for this virus.

Raptors could be especially hard hit

Wildlife experts have long known that highly pathogenic bird flus like this one were circulating in Europe and Asia. And they have worried about the possible threat these viruses might pose to American birds.

Then, in December of 2021, chickens and other fowl got sick and started dying on a farm on the island of Newfoundland, Canada. Tests showed this deadly bird flu virus had made it across the Atlantic.

"The very first moment it got to North America, it was a heads up to us," says Bryan Richards, the emerging diseases coordinator at the U.S. Geological Survey's National Wildlife Health Center.

In January, government officials announced its arrival in the U.S. after a wigeon duck in South Carolina tested positive. The last time a dangerous bird flu entered the country, Richards says, "the number of instances where we picked that particular virus up in wild birds was very, very limited."

In contrast, this latest bird flu virus is being detected in sick and dying birds all over.

"This outbreak in the wild bird population is a lot more extensive than we saw in 2014 and 2015," says David Stallknecht, an avian influenza researcher with the University of Georgia. "Just a lot more birds appear to be affected."

Waterfowl, and raptors that eat their dead bodies, are bearing the brunt of it.

In Florida, for example, more than 1,000 lesser scaup ducks have succumbed to the virus. In New Hampshire, about 50 Canada geese died in a single event. In the Great Plains states, wildlife experts have seen mass die-offs in snow geese.

"In addition, there's a host of other species, including black vultures and bald eagles and some of the other scavenging species, that were likely infected by consuming the carcasses of those waterfowl," says Richards.

It remains to be seen how much of a toll this virus will take on American bird species.

In Israel, when this virus hit an area where about 40,000 common cranes had gathered for the winter, "they lost a reported 8,000 of these birds over the course of a couple weeks," says Richards. "So when you start thinking about losing 20% of a specific population of wild birds, that's a pretty substantial impact."

Poultry farmers cull their flocks

Chickens and turkeys raised by the poultry industry have suffered the most deaths, and farmers are bracing themselves for even more.

The bird flu that struck in 2014 and 2015 resulted in the deaths of more than 50 million birds and cost the industry billions of dollars. Back then, the greatest number of cases occurred in the month of April.

"So I think I am kind of holding my breath this month," says Denise Heard, director of research programs for the U.S. Poultry & Egg Association.

The virus has a number of ways to get from wild birds into poultry, says Heard. Since the last outbreak, the industry has worked to educate farmers about how to protect their flocks.

"Wild migratory waterfowl are always flying over the top and when they poop, that poop gets on the ground," she says, explaining that the virus can then get tracked into bird houses on boots or inadvertently moved from farm to farm on vehicles.

Heard says there currently seems to be less spread of the virus from farm to farm than was seen during the last major outbreak. Instead, there are more isolated cases popping up, perhaps because wild birds are bringing the viruses to farms and backyard flocks.

If this virus sticks around in wild bird populations — which some scientists think is likely — poultry farmers may need to just learn to live with this problem.

"I hope that this is not the case. I hope that in the U.S. this infection will die off soon, and the virus will go away again like it did in 2014," says Ron Fouchier, a virologist at Erasmus Medical Center in the Netherlands. "But there's no guarantee for that, as we've seen in Europe now that this virus has remained present for several years in a row."

Since December, farmers in Europe have had to cull more than 17 million birds. "So that's very similar to the situation in the U.S.," says Fouchier. "And we are seeing massive die-offs in wild birds."

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