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Ag Again

Big Ag, Not Wild Birds, Is What Really Spreads Avian Flu

While wild animals can spread the virus, industrial farms are where it really thrives—and likely originated.

Turkeys are crowded together.
Nathan Howard/Getty Images
The Powers Farm white turkey flock is seen under shelter as part of an effort to prevent exposure to avian influenza, on November 14, 2022, in Townsend, Delaware.

Migratory birds are getting a bad rap right now, as avian influenza cases multiply and appear in new species. “The reason it’s become such a threat is because of how widespread it’s become in wild birds,” journalist Emily Anthes said of H5N1 on The Daily recently. “Wild water birds, in particular, are known for carrying these viruses.” The virus is “widespread among wild birds” in the U.S. and “sometimes infects poultry,” Wenqing Zhang, head of the Global Influenza Program at the World Health Organization, said at a news briefing in Geneva. “How do you stop the birds from migrating to the south for the winter? That’s the big, big thing there,” Lewis “Bud” Dinges, Texas state veterinarian and executive director of the Texas Animal Health Commission, told me recently when I asked how to stop outbreaks on dairy and poultry farms.

It’s true that migratory birds brought H5N1 to North and South America in late 2021, and they can continue spreading it around the globe. But this variant didn’t start with them. Bird flu was first identified among chickens on a farm in Scotland in 1959. In 1996, it began drawing more attention when it was found on a goose farm in Guangdong, China, and then spread to people, killing more than half of those with confirmed infections.

It was only in 2005 that H5N1 began spilling from poultry into wild birds, and it took 16 more years for the birds to bring it to the Americas—where it again began spreading in poultry farms. “It’s like a wildfire moving through a dry forest,” Matthew Hayek, an assistant professor of environmental studies at New York University, told me. Although this is assuredly an undercount, H5N1 has been detected in more than 9,000 wild birds, while the outbreak has affected more than 90 million poultry in the U.S., according to the U.S. Centers for Disease Control and Prevention.

Experts have been warning the public for decades about how industrial animal farming can make disease more likely, leading to the emergence of old or new viruses. Once bird flu gets into a large-scale poultry or, now, a dairy operation, it can spread quickly in cramped confines, and then spread to other farms before spilling back into wild birds and animals. Pigs and, it now appears, cows can also create potentially dangerous new versions of the virus that more readily infect people. It’s also possible that people may spread the virus by tracking the virus into and out of farms on their unwashed boots or transportation vehicles.

We’re getting the story of bird flu backward. The way that we farm animals in the U.S. and the world is amplifying costly and potentially deadly pathogens. Stopping this outbreak and preventing future outbreaks means reckoning with a troubling paradox: Food is essential for our health, but the conditions under which we create our food is making us and the animals around us sick.

With industrial food animal production, there are thousands, even tens of thousands, of genetically similar animals crowded together, sometimes on top of each other, often in their own waste. When those crowded conditions meet a virus that mutates as frequently and quickly as influenza does, “it’s a recipe for disaster,” Jessica Leibler, an associate professor of environmental health at the Boston University School of Public Health and an environmental epidemiologist, told me.

Hayek calls it the “infectious disease trap” of animal agriculture. “As long as we’re producing and consuming this many animals for our Western-style diets, there is no way out of the trap,” he said.

Pigs and cows typically only get tested when they get sick; it’s usually up to their veterinarian whether they order tests, and which ones they do. “In contrast to the poultry and the egg industry, where no influenza virus is tolerated, influenza A viruses are very much tolerated in all the U.S. pig facilities,” Gregory Gray, a professor of infectious diseases at the University of Texas Medical Branch and a public health physician who studies zoonotic respiratory viruses, told me. “There’s no systematic sampling of every pig that goes to the market for influenza viruses, and no sampling on the farms for influenza viruses unless there’s illness.”

That’s dangerous, because pigs are known as “mixing bowls” for influenza viruses; they have receptors similar to humans’ and can mix and match different variants that could be well-suited for spread among people. The more densely packed the pig farms are, “the greater the variety of influenza A virus variants,” Gray said. Cows may also have a similar blend of receptors, according to new research that has not yet been peer-reviewed or published.

While avian influenza hits poultry hard, it’s possible that pigs and cows, which have less deadly courses of illness, are spreading the virus with few or no symptoms. “Unfortunately, what always happens with surveillance efforts is that they’re expensive—resources are limited,” Leibler said. Wastewater monitoring, including of the manure and litter stream from commercial food facilities, could help. But that would require some participation from the farms, which have been reluctant to test at all.

Monitoring the workforce for pathogens would identify whatever is circulating on farms that could affect humans, since farm workers are often the first to be infected by zoonotic diseases, Leibler said. “Obviously, the gold standard would be both—to have active surveillance of animals and surveillance of humans,” she said—“surveillance” meaning periodic testing. “But at minimum, being able to have ongoing surveillance of the workers in these industrial facilities would be really important to try to understand what pathogens they’re being exposed to.” Farm workers’ households might also be the first place human-to-human transmission would show up. Identifying that early would be crucial to stopping transmission before it becomes a pandemic, she said. “We saw this also with Covid. There can be quite a number of background infections before you start to see cases spilling over into the clinic. And the earlier you can identify those cases, the better equipped we are to prevent the virus from spreading further.”

The lack of testing has been a major issue in this outbreak. So far, only about 25 people have been tested for H5N1, despite reports that dairy workers were getting sick around the same time the cows were.

The CDC only recommends testing symptomatic people in close contact with sick animals, and until recently, the U.S. Department of Agriculture was only testing up to 20 symptomatic cows per herd; that changed with the realization that infection can happen asymptomatically, and with news of how widespread inactivated viral particles are in commercial milk.

But the bigger barrier to testing seems to be coming from the farms, many of which have been reluctant to allow officials from the CDC and USDA to test workers and animals. One Texas agricultural representative warned that federal officials need to “back off.”

Gray understands farmers’ reluctance to test: “‘Why should we report this to the government when it’ll just hurt us more?’” he said. Poultry farmers who detect avian influenza get reimbursed by the federal government for culling their flock. But livestock farmers don’t have similar compensation schemes for drops in milk production and sick or dying cows. “So I don’t blame them, I really don’t,” Gray said. “If there was some sort of compensation, then there will be motivation to do better reporting.”

Financial help for farmers to reduce diseases could go beyond active outbreaks. While a poultry farmer may receive federal funds to replace sick flocks, they can’t get the same assistance to convert their operation to, say, grow mushrooms instead, Hayek said. “There are lots of incentives to keep producers producing longer than is economically viable. So change those incentives to give producers the most options—let them get out if they want to get out.”

Regulators and farmers should also pay more attention to ventilation, transportation, manure management, and labor practices on farms. The alphabet soup of federal agencies—CDC, FDA, USDA, OSHA, USFWS—coordinating the response to zoonotic outbreaks need to cooperate more smoothly, Leibler said. It might be time to vaccinate farm animals in the U.S., Gray said, despite logistical and financial challenges. “It looks to me like that’s the best course.” When it comes to measures like these that could prevent another pandemic, Leibler said, “we can’t really rely on the different companies to do it on behalf of the world.”

But controlling how far and how much this virus spreads means addressing long-standing gaps in agricultural policy. “We have a regulatory bubble of agriculture in the United States,” Hayek said. “They’re exempt from all sorts of laws that every other business is obligated to follow, including clean air and clean water.”

In order to reduce the risks of amplifying viruses like H5N1, a 2023 report from the Food and Agriculture Organization of the United Nations acknowledged, governmental agencies need to reassess “the nature and sustainability of poultry production systems.” Now that the virus is spreading among cows, cattle operations will likely need new consideration as well.

“What it takes is changing production and consumption, in addition to better access and the political will and courage to measure farms where potentially pandemic diseases are now endemic,” Hayek said. “It takes probably eating less meat and dairy than we do, and it also takes providing incentives for producers who want to get out to let them get out.”