FEB. 27, 2025, by S. Rust and K. Kaplan
Credit: Pixabay/CC0 Public Domain
When the deadly H5N1 bird flu virus made its first appearance at a U.S. poultry farm in February 2022, roughly 29,000 turkeys at an Indiana facility were sacrificed in an attempt to avert a larger outbreak.
It didn't work. Three years later, highly pathogenic avian influenza has spread to all 50 states. The number of commercial birds that have died or been killed exceeds 166 million and the price of eggs is at an all-time high.
Poultry producers, infectious disease experts and government officials now concede that H5N1 is likely here to stay. That recognition is
prompting some of them to question whether the long-standing practice of culling every single bird on an infected farm is sustainable over the long-term.Instead, they are discussing such strategies as targeted depopulation, vaccinations, and even the relocation of wetlands and bodies of water to lure virus-carrying wild birds away from poultry farms.
But each of these alternatives entails a variety of logistical, economic and environmental costs that may eclipse the intended savings.
"People talk about common-sense solutions to bird flu," said Dr. Maurice Pitesky, a veterinarian and commercial poultry expert at UC Davis. "But that's what mass culling is. There's a reason we've been doing it: It's common sense."
The current version of the bird flu—known as H5N1 2.3.4.4b—is both highly contagious and highly lethal. It has plowed through the nation's commercial chickens, turkeys and ducks with a mortality rate of nearly 100%.
"There's a reason why they call it 'highly pathogenic avian influenza,'" said Angela Rasmussen, a virologist at the University of Saskatchewan's Vaccine and Infectious Disease Research Organization. "It just goes straight through a flock like a hot knife through butter."
And it's why most researchers and veterinarians promote mass culling, describing it as humane and cost-effective.
A natural death from H5N1 is not pleasant for a chicken, said Rasmussen. The virus produces a gastrointestinal infection, so the birds wind up dying of diarrhea along with respiratory distress.
"It's like Ebola without the hemorrhage," she said.
Sparing birds that don't look sick is a gamble. They may be infected and able to spread the virus through their poop before they have any outward signs of illness. The only way to know for sure is to test each bird individually—an expensive and time-consuming prospect. And if even a single infected bird is missed, it can spread the virus to an entire flock of replacements, Rasmussen said.
Besides, she said, all of the extra work that would go into making sure some chickens can stay alive would only drive up labor costs and ultimately make eggs more expensive.
It also has the potential to increase the total amount of virus on farms, which is dangerous for human poultry workers, said Dr. Ashish Jha, dean of the Brown University School of Public Health.
"One of the reasons to cull early is that you don't want a lot of bird-human exposures," he said. "The more infections we introduce to humans, the more mutations we're going to see that increase the risk of a broader epidemic or pandemic."
For all of these reasons, international trade agreements require mass culling—also known as "stamping out"—so that importers don't get a side of H5N1 with their poultry, said Dr. Carol Cardona, a veterinarian and avian influenza researcher at the University of Minnesota.
That's not the only financial incentive for mass culling.
The USDA reimburses farmers for eggs and birds that have to be killed to contain an outbreak, but not for birds that die of the flu.Yet at times, this has meant killing more than 4.2 million birds, most of which may have been healthy.
Bill Mattos, president of the California Poultry Federation, said a more targeted approach could be feasible when all birds are not living under the same roof. In California, for instance, farms that raise broiler chickens typically operate multiple stand-alone buildings with separate ventilation systems, entryways and exits.
Biosecurity measures like these can keep pathogens from spreading between barns, Cardona said. Risks could be reduced further by requiring workers to change their clothes and boots when moving from barn to barn, or by assigning workers to a single barn, she said.
But others, including Dr. John Korslund, a veterinarian and former USDA researcher, are skeptical that such a practice could work, considering the virulence of H5N1.
"Chickens are infected and shedding virus very early, often before visible evidence of clinical illness," Korslund said. "Odds are that 'healthy' buildings on infected premises may be in reality in the early stages of incubating infections," he said.
While it was possible some buildings might remain virus-free, and some birds could be salvaged, the downsides of this approach are huge, Korsland said. "A lot of additional virus will be put into the environment," he said.
Indeed, flu particles from one facility can escape exhaust fans and travel great distances, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. Studies have shown that "the movement of virus from farm to farm was associated with wind direction and speed," he said.
Bird flu vaccines may offer some protection. Both China and France use them, and the USDA granted a conditional license this month for an H5N2 vaccine designed for chickens, according to Zoetis, the company that developed it.
While some are heralding vaccines as a potential tool to inoculate the nation's poultry farms, others say the costs could be too much.
Most U.S. trade partners are not keen to import poultry products from countries that vaccinate their birds due to concerns that the shots can mask the presence of the virus. And most will blackball a nation's entire poultry portfolio, even if just one region or type of poultry is infected.
The U.S. exports more than 6.7 billion pounds of chicken meat each year, second only to Brazil, according to the National Chicken Council. So as long as foreign buyers are resistant to vaccination, the shots probably won't be deployed even if egg-laying hens are getting wiped out by the virus.
As members of the U.S. Congressional and Senate Chicken Caucuses wrote in a letter this month to the USDA, "if an egg-laying hen in Michigan is vaccinated for HPAI, the U.S. right now would likely be unable to export an unvaccinated broiler chicken from Mississippi."
The new H5N2 vaccine might allay such concerns. While it would offer protection against H5N1, it would elicit antibodies that look distinct from the ones that arise from an actual infection, Cardona said.
Pitesky said that none of these measures will work if we don't do a better job with flu surveillance and farm placement.
Wildlife and agriculture officials should ramp up their testing of wild birds to determine where the virus is moving and how it is evolving, he said. That will require global coordination because infected birds can travel back and forth between the U.S., Canada, Russia, East Asia and Europe.
Poultry farms near ponds, lagoons or wetlands that attract wild birds should be on high alert during migration season, Pitesky said. Farmers should use apps such as eBird, BirdCast or the Waterfowl Alert Network to keep tabs on when the birds are nearby so they can step up their biosecurity measures as needed, he said.
It may be possible to lure wild birds away from agricultural facilities by bolstering wetlands in more remote areas, he said.
"I keep pushing the idea of starting to reflood some of those wetlands, but we haven't done it in any kind of strategic fashion," Pitesky said.
The idea makes sense, but has been brushed off as "pie in the sky, which I push back on," he said. "I'm like, what we're doing right now is obviously not working."
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