US resident infected with rare H5N5 bird flu, health experts say ‘No one actually knows…’

A Washington state resident has been diagnosed with bird flu, marking the first human case in the U.S. since February. Health officials announced Friday that the case involves a different strain of bird flu than previous infections, as reported by AP.

The patient, an older adult with underlying health conditions, remains hospitalised. The preliminary diagnosis was reported on Thursday and later confirmed on Friday.

The person was infected with a bird flu called H5N5, state officials said, AP reported.

State and federal health officials said it appears to be the first known human infection with the H5N5 bird flu virus.

That version is not believed to be a greater threat to human health than the H5N1 virus behind a wave of 70 reported human infections in the U.S. in 2024 and 2025. Most of those have been mild illnesses in workers on dairy and poultry farms.

Experts' insights

“I think it’s clear it’s not an easy leap for this virus to make, to switch from being a duck virus to being a human virus. I think that’s pretty clear, but I certainly wouldn’t put money on the fact that it can’t make that leap,” said Webby, director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds, as reported by CNN.

“It’s going to take a little bit of the biological stars aligning for that to happen. We could argue exactly how likely that is, but no one actually knows. Only time will tell us, unfortunately.”

“These viruses behave similarly,” said Richard Webby, a prominent flu researcher at St. Jude Children’s Research Hospital in Memphis, Tennessee. “My gut instinct is to consider it the same as H5N1 from a human health perspective.”

The Centers for Disease Control and Prevention on Friday issued a similar statement that said no information would suggest "the risk to public health has increased as a result of this case.”

The agency is awaiting a specimen from Washington to conduct additional testing.

The distinction between H5N5 and H5N1 lies in a protein involved in releasing the virus from an infected cell and promoting spread to surrounding cells.

The Grays Harbor County resident, who has not been identified, has a backyard flock of domestic poultry that had been exposed to wild birds, health officials said. They believe the domestic poultry or wild birds are the most likely source of exposure, but say they are still investigating.

In 2024 and early 2025, infections were reported in 70 people in the U.S. — most of them workers on dairy and poultry farms. One person died, but most of the infected people had mild illnesses.

While the U.S. had not reported a human bird flu infection in months, there have been recent cases in poultry flocks and livestock. Over the past month, nearly 70 U.S. poultry flocks—both commercial and backyard—have been affected, with more than 1.7 million birds impacted, according to the U.S. Department of Agriculture (USDA). The last confirmed case in livestock was about a month ago in Idaho dairy cows.

The CDC has stated that the risk to the general public remains low, though it is higher for individuals working with cattle and poultry or those in contact with wild birds.

(With inputs from agencies)