Millions of chickens were slaughtered due to bird flu threat
Emily Elconin/Bloomberg via Getty Images
This year saw the first known deaths from avian influenza in the United States, raising fears that the virus may cause a pandemic among humans. However, it has still contained the outbreak enough to warrant ending the emergency response, but public health experts warn the battle is far from over.
“This is still a pandemic in [non-human] animals,” says Megan Davis at Johns Hopkins University in Maryland. “And the virus is no less deadly now than it was before.”
The pathogen that causes the vast majority of cases, a subtype of avian influenza called H5N1, first emerged in poultry in China in 1996. It then reappeared in 2021, devastating global bird populations and spreading to several mammals, including foxes, seals and cats.
H5N1 is poorly suited to infect humans and is not transmitted from person to person. But it still poses a serious threat, killing nearly half of the nearly 1,000 people known to have contracted it worldwide. since 2003. These deaths likely represent severe cases, with milder cases remaining unreported. Still, there is a risk to people, and it would be even greater if the virus developed the ability to spread from person to person, a scenario that could trigger a pandemic, Davis says.
That's why public health experts were alarmed when H5N1 began circulating among US dairy cows in March 2024first known case of infection in dairy cattle. This not only brought the virus into close proximity to people, especially farm workers, but also provided one of the best opportunities for it to adapt and spread between people. Every time a pathogen infects a human or other mammal, it has a chance to acquire the mutations needed to person-to-person transmission” says Davis.
Since then, H5N1 has been detected in more than 1080 herds in 19 US states.and also persecute poultry farms. From February 2022 to mid-December, the disease infected at least 1,950 flocks across the country, forcing farms to cull nearly 200 million birds.
Outbreaks on farms subsequently led to a surge in human cases. Belonging 71 people of those who have ever tested positive for avian influenza in the United States as of December 2025, all but six contracted it from infected dairy cows or poultry. Of these six cases, three were infected from another animal, while the origin of the remaining three cases remains a mystery, although there is no reason to believe that they were infected from another person.
In most cases, people experienced mild symptoms, such as red eyes, and made a full recovery. However, a man in Louisiana with a background health conditions died from the H5N1 virus in January, the first known death from avian influenza in the United States.
Since then, the country has largely brought the outbreak under control. The last time someone tested positive for H5N1 was in February, he says. Emily HilliardSpokesperson for the US Department of Health and Human Services. However, a man from Washington state tested positive and died due to a different, albeit related, strain of bird flu.caused by H5N5, in November after exposure to infected poultry.
“What is somewhat encouraging is that the reinvestigation of the fatal H5N5 case has not identified any further human cases, but the pandemic potential of H5 viruses remains, especially given the ability of these viruses to infect mammals, including humans, and to spread between mammals,” Davis says. The US Centers for Disease Control and Prevention (CDC) says it is closely monitoring the situation and the risk to the public is low.
H5N1 infections in dairy cattle have also declined sharply, reported only by the United States Department of Agriculture (USDA). two herds tested positive between November and mid-December.
This decline ultimately led the CDC to end the emergency. bird flu response in early July, Hilliard says. The response, which began in April 2024, allowed the agency to deploy additional personnel and resources for surveillance and mitigation, she said.
There are several possible explanations for why the number of cases was rejected. First, in December 2024, the USDA launched its National Milk Testing Strategy, requiring dairy farms to submit raw milk samples for H5N1 testing. “Testing is central to any control strategy,” says Davis. “If you don't know where [H5N1] that is, then introducing additional protective measures or introducing quarantine on farms is simply impossible.”
In February, the USDA also announced a $1 billion strategy to combat the H5N1 virus in poultry plants, including increased funding vaccine research and biosafety measures. One of the goals was to increase protection from wildlife. “The vast majority [bird flu] Reduced levels of the H5N1 virus on farms also likely led to a decline in human disease, given that most infections occurred in dairy workers, Davis said.
However, this may also be due to seasonal variations. “We saw lulls in the summer followed by explosions in the fall and winter,” Davis says. “So what you typically find is that during the migration season, which we're in now, you start to see more cases.”
Migratory birds bring the virus to farms during their travels, which is likely why the number of H5N1 detections in backyard and commercial poultry operations has more than increased. 130 percent between September and October. “What we haven’t had is a lot of people getting sick,” Davis says. But it's unclear whether that's due to increased security measures or reduced surveillance of workers, she says.
“I’m encouraged that we’re seeing a decline in cases,” Davis says. “But I think we still have a lot to do.”
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