The bird flu has jumped to foxes, bears and other mammals. Are humans next?

• As a bird flu outbreak persists into its second year, scientists are on alert for its possible migration to other species, including humans.
• So far there have been only a handful of scattered cases in humans, and a researcher says the barriers to interspecies spread are high.
• But Iowa, with nation-leading populations of laying hens and pigs, could be a "major mixing vessel," a researcher warns, and it's being closely monitored.

This spring, state wildlife veterinarian Rachel Ruden is putting together a team that will test killdeers — shorebirds that nest along rural roads in Iowa — for highly pathogenic avian influenza, the disease that has been disrupting Iowa's nation-leading egg industry and driving up prices.

And there's another lurking worry, though fortunately so far unrealized: that the virus could jump to humans as well.

To contain the virus, U.S. producers have culled a record 58.7 million chickens, turkeys and other poultry, including 16 million domestic birds in Iowa. But the virus is now infecting foxes, bears and other mammals across 23 states, including Iowa. And scientists suspect it moved between animals at a commercial mink farm in Spain, wild seals in Maine and sea lions in Peru.

"It's under those environments we think that's sort of the sweet spot for this virus to make that switch from being a duck virus to being a human virus," said Richard Webby, an infectious disease researcher at St. Jude Children's Research Hospital in Memphis, Tennessee.

Scientists primarily suspect that animals were the source of the coronavirus that swept across the globe in 2020, though there's debate about the possibility of a leak from an immunology research lab. New evidence suggests it was transmitted to humans from raccoon dogs, fox relatives that were illegally traded at the Huanan "wet" market in China. The New York Times reported that one researcher even found a cage full of raccoon dogs there on top of a cage holding birds, "exactly the sort of environment conducive to the transmission of new viruses."

Iowa lies along a major migratory path for wild birds, and ducks and geese descend in vast clouds on Iowa lakes each spring. Wild waterfowl along with killdeer and other shorebirds can carry bird flu without apparent symptoms, spreading it to U.S. domestic flocks. Iowa, with about 58 million laying hens and 11.7 million turkeys, has been the epicenter of the outbreak, which began during the spring wild bird migration in 2022 and hung on through the winter.

More:Bird flu costs accumulate as avian influenza outbreak enters second year

The record 58.7 million culling since spring 2022 is a noteworthy uptick from a 2015 outbreak, the nation's previous record. Then, U.S. producers destroyed 50.5 million birds, including 32.7 million in Iowa. Controls that Iowa producers have used in the current outbreak are credited with holding the state's total to about half of 2015's losses.

So far, the threat to human health is low, Webby said. But that could change, given how widespread the virus is. "It's in many, many different countries, and in many, many different species," Webby said. "So the risk is low, but the opportunity is there for adaptation to take place."

And it has elsewhere, particularly from 2013-17, when bird flu outbreaks among humans in China spread to Hong Kong, Macau, Malaysia, Taiwan and Canada, infecting about 1,500 people and resulting in the deaths of 40% of those hospitalized, according to the U.S. Centers for Disease Control and Prevention.

Disease researcher: Iowa is 'a major mixing vessel,' important to monitor bird flu

Iowa's large poultry and livestock industries make the state an important area to monitor for spillover of the disease from birds to mammals, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. In addition to vast commercial poultry flocks, about 50 million pigs are raised in the state annually ― also the most in the nation.

"Clearly, Iowa is a location that we would call a major mixing vessel," said Osterholm, an epidemiologist. "Meaning, you've got the wild birds coming through in the flyway, and you've got the domestic bird and pig production, often in close proximity.

"Now, could that lead to a human virus that would then be capable of causing a pandemic? I can't say it won't," he said, adding that currently, however, "There's no evidence that we're seeing changes in the virus in which it would likely increase the risk to humans for a pandemic."

More:Iowa reports bird flu outbreak in backyard flock as spring migration begins

Over the past year, Ruden, the Iowa Department of Natural Resource wildlife vet. and other wildlife surveillance officials have tested wild birds and investigated large or unusual wildlife deaths. Red foxes and opossums, as well as eagles, owls and other raptors in Iowa, have died after eating infected birds, Ruden said.

But there have been some extenuating factors, The foxes, for example, were young, without well-developed immune systems to fight the virus, Ruden said.

So far this spring, she said, she's seeing fewer infections in wildlife compared to a year ago, giving her hope that the amount of virus being spread is lower — or that the birds and mammals exposed to it over the past year "may have developed antibodies against it," Ruden said.

Some eager for an avian influenza vaccine, but there are obstacles to overcome

Why not just stamp out the bid flu with a vaccine?

Sheila Larson, who raises turkeys with her husband, son and in-laws near Ellsworth in north central Iowa, is ready for that to happen.

A year ago, one of the Larsons' barns was hit with highly pathogenic avian influenza.

"I think everyone is nervous" about the return of migrating birds, said Larson, whose family worked intensively for two months to cull 26,000 turkeys, compost the birds, and clean and disinfect their barns. Officials tested the facility to ensure the virus was gone before allowing the family to bring birds back in.

"This virus is not going away. We have to figure out how to fight it and keep birds healthy," Larson said.

With egg prices spiking 32% last year, and forecast by the USDA to climb nearly 38% this year, the Biden administration feels pressure to act. But U.S. Agriculture Secretary Tom Vilsack told the Senate Agriculture Committee in March that developing a vaccine that is effective "is a long way away."

Rosemary Sifford, the USDA's chief veterinary officer, said the agency is testing vaccines, but "we want to make sure that any vaccine we would use would be well-matched to the current outbreak strain," she said.

More:2023 USDA outlook calls for big yields, lower crop prices; more pigs, fewer cattle

Additionally, inoculating millions of birds is a logistics nightmare. "Each individual bird would have to be handled ... and they'd need boosters," said Sifford, adding that the agency is looking for ways to administer a vaccine through the birds' drinking water or "in ovo," while the embryo is in late-stage development, rather than with traditional injection.

And there are thorny trade issues. Some researchers worry that a vaccine could make matters even worse, masking outbreaks until deadly mutations take place and it's too late to stop them. That's especially a concern with exporting live birds.

"There are a number of countries that will basically shut off exports … if the poultry has been vaccinated," Vilsack told lawmakers.

Sifford said the U.S. would need affordable tests that can distinguish between the vaccine and the virus affecting wild birds to help satisfy trade concerns.

Yuko Sato, an Iowa State University assistant professor in veterinary diagnostics, said getting agreement within the U.S. poultry industry to use a vaccine would be difficult, "especially when we have all these other questions about the vaccine."

What would trigger the U.S. to use a vaccine? Sifford said the nation would need to see the outbreak could not be "controlled appropriately through our traditional stamping-out methods, such that we might see the virus spreading through domestic flocks, without us having the ability to slow it down or stop it.

"And that is definitely not the case so far in this outbreak," she said.

Why bird flu faces obstacles to human spread

While there are big obstacles to implementing a vaccine, there also are major obstacles for the virus to jump between species.

Webby said three complicated changes are required before the virus could adapt to humans.

"One of those changes the virus can do pretty readily," he said. "The other two are quite large barriers to overcome."

Still, Webby said, scientists "get a little bit more worried when we see mammalian infections. ... We think if this virus is going to change, there's probably more chance it was going to change in a mammalian host."

The World Health Organization director-general, Tedros Adhanom Ghebreyesus, warned earlier this year that the virus spillover into mammals should be monitored closely. "For now, the risk to humans is low ... but we cannot assume that will remain the case," he said.

Some scattered cases in humans have been reported in the current outbreak. Last year, a Colorado man tested positive for the H5N1 avian influenza after helping to clean an infected poultry facility. This year, a 9-year-old girl in Ecuador became ill after coming into contact with an infected backyard flock. And an 11-year-old girl died and her father tested positive, though he was without symptoms, in Cambodia.

The virus hitting the Ecuadorian family was a different variant than is now circulating in birds, the CDC said in March.

"Looking at the viruses that have been sequenced … it really doesn't look like the virus had made those key changes yet, which, of course, is a good thing," Webby said. "It's more evidence that the barriers that this virus has to become human viruses are pretty high."

As for Iowa, Osterholm, the Minnesota scientist, said the state "has not had a human case this year, and you've been swimming in the virus."

More:A dog died after getting bird flu in Canada. Here's how to keep your pets safe.

Donnelle Eller covers agriculture, the environment and energy for the Register. Reach her at deller@registermedia.com or 515-284-8457.