Novel H5N5 Bird Flu Hospitalizes Washington Resident; Officials Urgently Investigate

Washington confirms first human case of H5N5

Health authorities in Washington state have confirmed a human infection with a previously unseen avian influenza, H5N5. The virus was first detected in 2023 in birds and mammals in eastern Canada, and state officials announced the Washington case on Friday.

Patient and exposure

The case involves an older resident of Grays Harbor County on the Olympic Peninsula who has underlying health conditions. Their illness worsened in early November, prompting transfers to hospitals in Thurston County and later King County (Seattle). The patient kept a backyard flock of mixed domestic poultry, which health officials say — along with wild birds — is the most likely source of exposure.

Expert concern and investigation

'Given the rarity of such infections in humans and the fact that this person was hospitalized, there is an urgency to figure out how this person may have come in contact with the virus and whether anyone else was infected,'

said Jennifer Nuzzo, director of the Pandemic Center at Brown University.

Epidemiologists and virologists caution that avian influenza viruses can become a greater threat if they spread and mutate in mammals or humans. Related strains, such as H5N1 detected in North American dairy cattle, are examples of bird influenzas that could require only a small genetic change to spread more easily between people.

What researchers have found so far

Researchers have reported H5N5 infections in multiple species. Henry Niman, an evolutionary molecular biologist and founder of Recombinomics Inc., noted that infected Canadian animals have included a red fox, a cat and a raccoon. Studies published last year found some infected animals carried mutations that could help the virus transmit more readily between mammals.

Samples from a critically ill teenager in Canada previously showed the virus had acquired genes that aided targeting human cells and causing severe disease. Every human spillover increases opportunities for the virus to replicate and potentially acquire mutations, especially if a person is co-infected with another influenza virus.

Public health response and guidance

Melissa Dibble, a spokesperson for the U.S. Centers for Disease Control and Prevention, confirmed the Washington health department's finding and said the CDC is investigating the case with state officials. The agency continues to assess risk and currently considers the likelihood to the general public to be low.

Nevertheless, the CDC recommends caution for people who work with or handle birds, cattle or other potentially infected domestic or wild animals: wear gloves, masks and eye protection. It also advises avoiding raw or undercooked meat and eggs, and steering clear of raw milk or unpasteurized cheeses for people and pets.

Outlook

Some experts urged vigilance but not panic. Richard Webby, an influenza researcher at St. Jude Children's Research Hospital, described the virus as 'interesting' and said there is currently 'no reason to expect an elevated risk.' By contrast, others stress that a severe presentation in the first known human case is concerning and merits careful investigation and genetic analysis of the virus.