In early November 2025, public health authorities in Washington state confirmed what appears to be the first-ever human infection with the H5N5 strain of avian influenza.
The Washington State Department of Health announced that a Grays Harbor County resident who was already hospitalized with flu-like symptoms has tested positive for the Influenza A H5 virus.
Further laboratory testing identified the virus as H5N5, a subtype previously seen in animals but never previously documented in humans.
Patient profile
The confirmed case is an older adult with serious health problems. According to state officials, the patient developed a high fever, confusion and respiratory distress.
The person stays in hospital and authorities are closely monitoring health care employees and other contacts, although no additional infections have been identified to this point.
Probable source of infection
Researchers suspect that the source of the infection was the patient’s backyard flock of poultry, on condition that these domestic birds had contact with wild birds, which frequently carry various avian influenza viruses.
The Washington State Department of Health is working with agricultural authorities to research exposure routes from each animals and the environment.
Public health assessment
Despite the novelty of this infection with the human H5N5 virus, public health experts don’t currently consider it a significant threat to the final population.
Both the Centers for Disease Control and Prevention (CDC) and Washington health officials have said the danger to the general public stays low. They emphasize that to this point there isn’t a evidence of everlasting transmission of this strain from individual to individual.
Comparison with other strains of bird flu
H5N5 belongs to the identical broader family of H5 bird flu viruses that cause sporadic infections in humans in other forms – most notably H5N1.
The H5N1 subtype has been probably the most continuously reported in humans in recent times, while H5N5 has been detected in wild birds but has not previously been known to contaminate humans.
According to an influenza researcher at St. Children’s Research Hospital. Jude, the H5N5 strain “behaves similarly” to the H5N1 virus by way of its risk to human health.
Meaning
The confirmation of H5N5 in humans is a noteworthy event for several reasons. Expands our knowledge of the zoonotic potential of bird flu, i.e. the flexibility of bird flu viruses to spread from birds to humans.
Such cross-species unwanted side effects are rare, but after they occur they deserve close scientific scrutiny. This case highlights that even strains previously present in animal reservoirs can infect humans under the suitable conditions.
At the identical time, sanitary authorities appeal for calm. The proven fact that the H5N5 virus has not yet been documented in a couple of case suggests that its ability to spread amongst humans could also be limited – not less than in its current form, in response to the CDC.
Precautions and ongoing investigation
In response to this case, public health and veterinary authorities are intensifying their investigations. Epidemiology teams interview patient contacts, monitor symptoms, and conduct tests as needed.
On the animal side, efforts are underway to trace the route of infection through the patient’s poultry flock and any possible contact with wild birds.
American authorities are also strengthening general preventive recommendations: people raising backyard poultry or having contact with wild birds are asked to make use of personal protective equipment, especially when involved with birds.
They also appeal to right away report sick or dead animals and avoid direct contact with potentially infected birds.
