A man in Washington has been diagnosed with a strain of the bird flu that’s never been detected in humans before. The individual ― an older adult with underlying conditions who has been hospitalized since early November ― tested positive for a subtype called H5N5.
According to a press release from the Washington State Department of Health, the man likely contracted the virus from the domesticated poultry he kept in his backyard, which were exposed to wild birds known to carry several strains of the bird flu.
Public health officials say human-to-human spread is unlikely.
“The risk of avian influenza in humans is primarily confined to those who interact with infected avian species, infected cattle species and (potentially) unpasteurized milk drinkers. The risk to the general public is currently low outside those risk groups,” Dr. Amesh Adalja, an infectious diseases expert and senior scholar at the Johns Hopkins University Center for Health Security, told HuffPost.
What should we know about this subtype of the bird flu?
In 2021 and 2022, the H5 subtype of the bird flu developed mutations that allowed it to infect, or spill over, into many more types of mammals more easily, according to Benjamin Anderson, an assistant professor and One Health Center of Excellence associate director at the University of Florida College of Public Health and Health Professions.
As a result, migratory waterfowl started spreading the virus, causing large outbreaks among poultry, wild animals, and, as of last year, cows on dairy farms.
Infected animals can spread avian flu to humans via their saliva, mucous, feces, or other Bodil fluids (like milk), according to the Centers for Disease Control and Prevention.
Every year, there are sporadic avian influenza cases in people, including H5N1, H7N9, H9N2, H5N6 and H7N7, according to Adalja. In the United States alone, there have been 70 cases of avian flu since 2024.
But this is the first time H5N5 has been detected in a human. According to Adajla, there were likely wild birds that harbored H5N5 that passed it to the man’s domestic poultry that eventually transmitted it to him.
“Now that the virus is so prevalent and recurring seasonally ― in the fall and winter ― as migratory birds move, it is not surprising that a human case associated with backyard poultry has occurred, as this is one of the environments where we have seen a greater amount of transmission risk over the last two to three years,” Anderson said.
Could this case trigger a bigger outbreak ― or, worse, a pandemic?
Avian influenza, in general, can cause one-off infections in humans, but does not spread readily between people right now, Anderson said. That said, there is always a concern that influenza viruses could evolve and gain the ability to spread between humans.
For this to happen, the virus would need to undergo several mutations that enable it to bind to human receptors, according to Adalja. The virus could also reassemble and create a new offshoot in an animal simultaneously infected with an avian influenza strain and a human strain, he added.
But is this likely? Probably not.
“Every bird flu strain has pandemic potential but this particular strain seems to have less pandemic potential than others since there has only ever been one human case (the current one), indicating that it is not especially prone to infect humans,” Dr. David Diemert, a professor of microbiology, immunology and tropical medicine at the George Washington University School of Medicine & Health Sciences, told HuffPost.
The most likely scenario: There may be sporadic, isolated H5N5 cases in people linked to avian exposure, as is typical with avian influenza strains, according to Adalja.
Still, the potential risk highlights the need for ongoing surveillance. Health officials say anyone who’s been in contact with the affected individual should monitor themselves for symptoms and seek testing and treatment if they suspect they’ve contracted the virus.
So far, no other people have tested positive for H5N5.
Here’s what you can do to stay safe
If you keep backyard birds or have contact with poultry or dairy cattle, keep an eye out for any signs of illness in your animals. Steer clear of any sick or dead animals that may be infected, the CDC advised.
If need be, wear personal protective equipment when handling the animals. And if any of your animals appear sick or experience an unusual death, report it to the United States Department of Agriculture.
“The only way it seems that this strain could be contracted is by having close contact with birds, such as having flocks of birds that are kept outside and that could come into contact with wild birds that carry the virus,” Diemert said.
Poultry is safe to eat — as always, it should be cooked to an internal temperature of 165°F.
It’s also a good idea to get vaccinated against the flu.
“Even if the strains of the virus covered by the vaccine do not exactly match the bird flu strain, there is likely still protection that will be induced that could protect against severe disease,” Diemert noted.
