Bird Flu Is Still Mostly a Concern for the Birds

Birds are having a rough year. During an unusually brutal avian flu season, more than 58 million wild and domestic birds in the United States have contracted the H5N1 virus, devastating farms and contributing to soaring egg prices.

What’s more, the virus has spread far beyond its typical avian hosts. Scientists have detected H5N1 in more than a dozen species in the U.S., including foxes, raccoons, bears, and bottlenose dolphins.

It’s extremely rare for humans to contract bird flu unless they come into close contact with infected animals. But the uptick in mammalian cases is catching scientists’ attention and renewing conversation about whether the disease could spill over into humans, too.

“This is quite an unusual situation,” Kaitlin Sawatzki, PhD, a post-doctoral researcher of infectious diseases at the Cummings School of Veterinary Medicine at Tufts University, told Verywell. “To the best of my knowledge, not only have we not previously seen evidence of mammal-to-mammal [transmission], but we also haven’t seen any large-scale mammalian outbreaks.”

The risk to humans remains low. Currently, only one human case has been reported in the U.S. But the more the virus circulates among animals, the more likely it may be to mutate and find new ways to infect mammalian hosts.

How Does Bird Flu Infect Other Animal Species?

Sawatzki’s research team is tracking infected seals in the northeast U.S. She said that in this and other cases, it’s possible that the animals ate infected birds or were otherwise exposed to the virus through their environment.

Avian flu spreads mainly through the gastrointestinal tract rather than through inhalation of respiratory droplets, as human influenzas do. That means animals that eat or otherwise come in contact with infected animals or their excrement may get sick.

An outbreak at a mink farm in Spain last fall provides the strongest evidence yet that the H5N1 virus can be transmitted from one infected mammal to another. The animals were infected with a new variant, which includes a genetic change that enables some animal-flu viruses to reproduce in mammals.

The virus quickly spread throughout the farm, indicating the minks could be infecting each other. Farm workers culled all 52,000 minks on the farm. Eleven farm workers came in contact with the mink, but they all tested negative for H5N1.

Despite the evidence from the mink farm, scientists haven’t yet found strong indicators of adaptations that would allow H5N1 to spread between mammals, said Kimberly Dodd, DVM, PhD, MS, director of the veterinary diagnostic laboratory at Michigan State University. It’s possible that H5N1 could evolve and eventually collect mutations that further allow it to infect and be transmissible between animals.

“Viruses mutate and this virus—because it’s so widespread and so well established in so many parts of the world—will continue to change and mutate. Whether that means that it’s able to infect humans at some point is a question we don’t have an answer to yet,” Dodd said.

Will Bird Flu Cause an Outbreak in Humans?

Since it first appeared in the 1990s, researchers have studied the virus and its potential to cause outbreaks in humans.

Prior to the COVID-19 pandemic and the 2009 H1N1 swine flu pandemic, H5N1 was considered to be the virus with the most pandemic potential. “The rationale for particular concern about an H5N1 pandemic is not its inevitability but its potential severity,” the authors of a 2007 scientific review wrote.

This is partly because humans don’t have many protective antibodies against the virus. The influenza vaccine has never included an H5 strain, and people generally don’t carry H5N1-fighting antibodies due to a lack of exposure to the virus.

There were four cases of H5N1 in 2022, according to the World Health Organization. A 9-year-old girl in Ecuador recently fell ill with the bird flu. Health officials said she had come in contact with backyard poultry before getting sick. Only one poultry worker in the U.S. got sick from the virus in recent outbreaks.

These cases aren’t nearly enough for scientists to generalize about how the virus would act in humans if there were significant spillover or human-to-human transmission.

Though H5N1 is considered a highly pathogenic avian flu, experts are quick to clarify that the risk remains really low for humans. People who are at the highest risk of getting sick with H5N1 are those who work in high-exposure environments, like those handling chickens on big poultry farms.

People can become infected if they breathe in air that has virus-laden droplets, or if they touch their eyes or mouth after touching a surface or animal carrying the virus, according to the Centers for Disease Control and Prevention.

“You really have to come into contact with a lot of virus and have this high exposure and high risk in order to be infected,” Sawatzki said.

Is It Still Safe to Eat Eggs and Chickens?

Commercial farms and U.S. regulatory bodies often test poultry products for traces of infection and there haven't been any cases of H5N1 in the general U.S. population.

“With cooked chicken and cooked eggs, you are good to go. There is no problem there. The virus absolutely cannot handle an oven,” Sawatzki said. “In general, in the U.S., a chicken that is sick is not going to make it to market.”

People who work closely with chickens and other birds should keep an eye out for sudden death, lethargy, decreased egg production, and other symptoms of illness in poultry, according to the USDA. Wearing personal protective equipment around animals is really only necessary for birds that show clear signs of sickness.  

“This is a really deadly flu for these chickens. If they get it, they are going to succumb to infection, and it's not pretty,” Sawatzki said. “So, if you have a backyard flock and it’s looking healthy—nobody has strange, unusual neurological symptoms, for instance—you can rest assured that those eggs and that chicken is going to be fine.”