A resident of Washington State has died from a rare strain of avian influenza, marking the first confirmed human fatality from the H5N5 subtype in the United States. The death, announced Friday by the Washington State Department of Health, occurred after the individual—an older person with pre-existing health conditions who raised backyard poultry—was hospitalized in early November.
The Shift in Strain: This case differs significantly from the recent surge in bird flu infections that have ravaged poultry farms and wildlife. While the dominant strain circulating since late 2021 has been H5N1, this death was caused by H5N5. Both are classified as H5 viruses, meaning they share a common hemagglutinin protein. The critical distinction lies in their neuraminidase proteins, which determine how the virus spreads and interacts with hosts.
Why This Matters: The emergence of H5N5 in a human is not necessarily a sign of increased danger, according to virologist Richard Webby of St. Jude Children’s Research Hospital. However, it does raise concerns about the virus’s ability to mutate and spread. Influenza viruses readily exchange genetic material with other strains circulating in animals, potentially creating new variants that could be more infectious or cause more severe illness in humans.
Tracking the Virus: Scientists have been tracking H5 viruses for decades through surveillance programs monitoring wild bird populations. The H5N5 strain identified in the human case appears to be linked to viruses circulating in shorebirds and gulls in eastern Canada, suggesting it migrated westward rather than emerging spontaneously in humans. This means the virus was already present in the environment, not a sudden, novel mutation.
Limited Human-to-Human Spread: As of now, public health officials have monitored close contacts of the deceased but have found no further human infections. The risk of transmission between people remains low, but the case underscores the dangers of exposure through backyard poultry. The previous U.S. bird flu death, in Louisiana earlier this year, also involved an older person with underlying health conditions who raised chickens.
Preventive Measures: Experts recommend strict biosecurity practices for those keeping backyard poultry:
- Separate domestic birds from wild populations.
- Use dedicated clothing and footwear for poultry care.
- Wear protective gear (masks, goggles) during coop cleaning.
- Thoroughly wash hands after handling chickens, eggs, or the coop.
Beyond poultry owners, the public should avoid contact with dead or sick wild animals.
In conclusion, while this fatality is alarming, it does not yet signal an increased pandemic risk. However, it serves as a critical reminder of the virus’s adaptability and the need for continued surveillance and vigilance in both animal and human populations. The emergence of new subtypes like H5N5 reinforces the importance of proactive public health measures to mitigate the threat of future outbreaks.
