First Worldwide Human Case of H5N5 Avian Influenza Reported in Washington

Public health officials have identified the first human case of highly pathogenic avian influenza (HPAI) A(H5N5) worldwide. The case, reported in Washington state, underscores the ongoing risk of avian influenza jumping from birds to humans, a phenomenon that continues to cause significant concern for medical professionals due to the potential for severe illness and broader transmission.

The Fatal Case in Washington

In November 2025, Washington reported a fatal human infection of HPAI A(H5N5). According to a report from the Centers for Disease Control and Prevention (CDC), the individual infected was a backyard flock owner. This marks the first time this specific subtype, H5N5, has been documented in a human being.

The severity of this case stands in contrast to many other recent human infections with H5 viruses, highlighting the unpredictable nature of how different avian influenza strains affect human health. The findings were also detailed in the New England Journal of Medicine, which noted that H5N5 can cause severe illness when transmitted to humans.

The Broader Landscape of H5 Viruses

While the H5N5 case is a new development, highly pathogenic avian influenza A(H5) viruses have been circulating among wild birds in the United States since 2022. These viruses are known for their high mortality rates in bird populations and their ability to cross species barriers.

The CDC has tracked a rising number of human infections associated with these strains:

• Recent Trends: Since 2024, 70 human cases of influenza A(H5) have been reported in the United States, though most of these resulted in mild illness.
• Washington State History: Prior to the H5N5 case, 14 human cases of influenza A(H5N1) had already been identified within Washington.

What is HPAI A(H5N5)?

Highly Pathogenic Avian Influenza (HPAI) refers to strains of the influenza A virus that cause severe disease in poultry. The “H” and “N” refer to the proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). While H5N1 has been the most widely discussed strain in recent years, the emergence of H5N5 in a human demonstrates that other subtypes within the H5 group can also pose a lethal threat to people.

The primary risk of these viruses is their potential to adapt for more efficient human-to-human transmission, which could lead to wider outbreaks. Currently, most human cases are linked to direct exposure to infected birds or contaminated environments.

Risk Factors and Prevention

The Washington case highlights a critical risk factor: the ownership of backyard flocks. Individuals who maintain small-scale poultry operations often have close, frequent contact with birds, increasing the likelihood of zoonotic transmission.

To reduce the risk of infection, health experts recommend:

• Avoiding direct contact with wild birds or sick/dead poultry.
• Using personal protective equipment (PPE) when handling birds.
• Practicing strict hygiene, including frequent handwashing after any potential exposure to animal environments.

Key Takeaways

• First Global Case: A fatal human infection of HPAI A(H5N5) was reported in Washington in November 2025.
• High-Risk Group: The infected individual was a backyard flock owner, emphasizing the danger of direct poultry contact.
• Widespread Circulation: H5 viruses have been present in U.S. Wild birds since 2022.
• Varying Severity: While many H5 cases since 2024 have been mild, the H5N5 strain has shown the capacity to cause severe, fatal illness.

Frequently Asked Questions

Can H5N5 spread from person to person?

The current reports focus on zoonotic transmission (bird-to-human). While public health officials remain concerned about the possibility of human-to-human transmission, the primary driver of these cases remains direct exposure to infected animals.

Is this part of a larger outbreak?

Yes, this is part of a broader trend of HPAI A(H5) viruses circulating in the U.S. Since 2022. While H5N1 is more common, the emergence of H5N5 indicates that multiple subtypes are circulating and capable of infecting humans.

What are the symptoms of avian influenza in humans?

Symptoms can range from mild—similar to a common cold or seasonal flu—to severe respiratory distress and pneumonia, as seen in fatal cases.