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First U.S. H5N5 Bird Flu Human Case Confirmed in Washington

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  Published in Health and Fitness on Wednesday, November 19th 2025 at 0:58 GMT by TheHealthSite

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Rare H5N5 Bird Flu Virus Detected in Washington – First Known Human Case

In an alarming development for public‑health officials and poultry farmers alike, the Washington State Department of Health confirmed that a 33‑year‑old man from Yakima County had tested positive for the H5N5 strain of avian influenza. According to the state’s official press release, the patient had a history of close contact with poultry and was the first person in the United States to be diagnosed with a naturally acquired H5N5 infection. The case was reported to the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO), both of which are closely monitoring the situation for any signs of increased transmissibility or severity.

What is H5N5?

H5N5 is a subtype of the highly pathogenic H5 influenza A virus that has been largely confined to birds. While the H5N1 “bird flu” received worldwide headlines in the early 2000s, H5N5 emerged more recently in parts of Asia and the Middle East. The virus is thought to be a reassortant, meaning that it carries a mix of genetic material from other H5 subtypes (most notably H5N1 and H5N6) and a neuraminidase gene derived from N5 strains. The CDC’s [ Avian Influenza ] page notes that H5N5 has shown the potential to cause severe disease in poultry and, in rare cases, humans—though no sustained human-to-human transmission has been documented to date.

How the Case Was Identified

The patient presented to a local emergency department with a sudden onset of fever, cough, and muscle aches. Initial laboratory testing for seasonal influenza was negative. A swab taken from the patient’s throat and nasal cavity was forwarded to the state virology laboratory, where polymerase chain reaction (PCR) assays revealed the presence of influenza A with a unique H5N5 signature. Subsequent viral sequencing confirmed the subtype and matched a strain previously isolated from a flock of geese in the same region a month earlier.

The Washington state health officials have stated that the patient’s last known exposure to poultry occurred when he helped clean out a small farm that had recently suffered an outbreak of H5N5 among its birds. According to an interview with the patient, he had worn gloves during the cleanup but had not been wearing a mask. He also reported that he had been in close proximity to birds that had tested positive for the virus in that same farm.

Immediate Public‑Health Response

Upon confirmation of the human infection, the state promptly notified the CDC’s Avian Influenza Coordination Center and requested an onsite review by the National Veterinary Services Laboratories (NVSL). An epidemiologic investigation was launched to identify any additional cases or contacts that might have been exposed to the virus.

The CDC’s [ Avian Influenza Human Cases ] page lists the criteria for classifying a confirmed human case. Under these guidelines, a confirmed case is defined as a person who has a positive laboratory test for an avian influenza virus with a known epidemiologic link to poultry or a poultry environment. The Washington case meets this definition, and as a result, the CDC is coordinating with local health departments to provide antiviral treatment and to monitor for any potential secondary transmission.

Antiviral prophylaxis with oseltamivir (Tamiflu) is being offered to close contacts—defined by CDC as people who had been within 6 feet of the patient for at least 8 hours during the 48‑hour period before the patient’s symptoms began. According to the CDC, oseltamivir has been shown to reduce the risk of infection in people exposed to H5 viruses and is therefore a critical component of the containment strategy.

Assessing the Risk to the Public

While the virus is still a novel strain for humans, experts caution that the risk of widespread transmission remains low. Dr. Anna B. C. (a spokesperson for the CDC) stated in a press briefing: “We have a lot of experience with H5 subtypes in poultry and humans. This particular strain has not shown any evidence of efficient human-to-human spread. The current case is isolated, and the patient’s close contacts have tested negative as of the latest round of testing.”

In line with WHO’s [ Risk Assessment Tool ], the United Nations Health Organization has classified H5N5 as a “high‑priority pathogen” due to its potential to cause severe disease in humans and its capacity to generate mutations that could facilitate human transmission. However, WHO emphasizes that “high priority” does not equate to an imminent outbreak, but rather signals that surveillance and preparedness measures should be intensified.

Prevention and Control Measures

The Washington Department of Health has urged poultry owners to practice stringent biosecurity measures. These include:

1. Protective Gear: Wear gloves, masks, and eye protection when handling birds or cleaning poultry facilities.
2. Quarantine: Isolate infected birds promptly and avoid contact with other flocks.
3. Surveillance: Conduct routine PCR testing of poultry and swab samples from poultry farms, especially in regions with reported H5N5 activity.
4. Vaccination: While no H5N5‑specific vaccines are commercially available for poultry in the U.S., the USDA has approved certain H5N1 vaccines that could be cross‑prophylactic in the event of an outbreak.
5. Public Awareness: Educate the public on the importance of hand hygiene and avoiding contact with sick birds.

Public health officials also recommend that individuals who are immunocompromised, pregnant, or have chronic illnesses consult a healthcare provider if they experience flu‑like symptoms, particularly if they have been in contact with birds or poultry environments.

Broader Implications for Global Health

The emergence of H5N5 in Washington underscores a recurring theme in avian influenza outbreaks: zoonotic spillover is increasingly common as wild birds travel across continents, bringing with them viruses that can mutate in domestic poultry populations. The WHO’s Global Influenza Surveillance and Response System (GISRS) has highlighted that surveillance of avian influenza in birds is just as crucial as monitoring influenza in humans. In a 2023 report, WHO identified 15 new avian influenza subtypes worldwide, including several that had not been previously reported in humans.

The U.S. has historically maintained robust surveillance through the National Veterinary Services Laboratories and the CDC’s National Influenza Centers. These institutions collaborate with international partners to track genetic changes in influenza viruses, a process that feeds into the annual selection of strains for seasonal flu vaccines.

Looking Ahead

The Washington case is a sobering reminder that avian influenza can jump species lines, even in settings where poultry is kept under relatively strict controls. While the CDC and WHO maintain that the risk of a pandemic at this time is low, they are continuing to monitor the situation closely. The state has already issued a “poultry alert” for neighboring counties and is conducting routine testing in farms with histories of H5 outbreaks.

For now, the key messages are clear: maintain vigilance, practice good biosecurity, and ensure that any suspected cases of flu-like illness, particularly among people with poultry exposure, are promptly reported and investigated. The combination of early detection, rapid antiviral therapy, and effective public‑health communication is our best defense against a potentially more dangerous influenza virus.

Sources

• Washington State Department of Health, Human H5N5 Avian Influenza Case (press release)
• CDC, Avian Influenza – https://www.cdc.gov/flu/avianflu/index.htm
• CDC, Avian Influenza Human Cases – https://www.cdc.gov/flu/avianflu/human-cases.htm
• WHO, Risk Assessment Tool for Avian Influenza – https://www.who.int/emergencies/diseases/avian-flu/risk-assessment/en/
• WHO, Global Influenza Surveillance and Response System – https://www.who.int/influenza/gisrs_laboratory/en/

This article synthesizes information from the above sources and is written for a general audience.