First Human Death from H5N5 Bird Flu Strain Confirmed
Health authorities have reported the first known human fatality from the H5N5 avian influenza virus, marking a significant development in the ongoing monitoring of bird flu strains. The victim, an elderly resident of Grays Harbor County in Washington State, succumbed to the infection on November 21 after being hospitalised earlier in the month.
The patient, who had underlying health conditions, first developed severe flu-like symptoms in early November. These included high fever, respiratory distress, and confusion, leading to their admission to hospital. Laboratory tests confirmed the presence of the H5N5 avian influenza virus on November 14.
Understanding the H5N5 Virus
H5N5 belongs to the family of influenza A viruses that primarily infect birds. Like the more widely known H5N1 strain, H5N5 is classified as a high pathogenicity avian influenza, meaning it causes severe disease in poultry. The classification refers to its impact on agricultural birds rather than necessarily predicting its effects on humans.
The naming convention for influenza A viruses reflects differences in two surface proteins: haemagglutinin (HA) and neuraminidase (NA). While H5N1 and H5N5 share the same H5 subtype of haemagglutinin, they have different neuraminidase proteins. Genetic analysis confirms this H5N5 strain is distinct from the H5N1 variant currently circulating in global bird populations.
Transmission and Risk Assessment
Investigators believe the infection likely occurred through contact with backyard poultry kept by the patient. The birds had known exposure to wild birds, which are natural carriers of H5N5 viruses. This represents a classic spillover event where an animal virus jumps to a human host.
Despite this tragic outcome, health officials emphasise that the risk to the general public remains low. There is no evidence of person-to-person transmission, which is the critical threshold for pandemic concern. Most avian influenza infections in humans remain isolated events, though their severity can vary unpredictably from mild conjunctivitis to severe respiratory illness.
Scientists monitor several warning signs that might indicate a virus is adapting to human transmission, including:
- Sustained human-to-human spread
- Genetic changes favouring human cell infection
- Clusters of cases without animal exposure
None of these red flags have been observed in this case.
Broader Implications and Monitoring
While the immediate threat to human populations appears contained, H5N5 represents both an ecological and agricultural concern. Controlling avian influenza in poultry currently relies on surveillance, enhanced biosecurity measures, and as a last resort, culling infected flocks. Vaccines exist but face political and economic barriers to widespread implementation in the United States.
In the long term, avian influenza viruses like H5N5 demand careful monitoring because of their pandemic potential. Influenza viruses have demonstrated greater ability to jump between species than other viruses, though this remains a difficult evolutionary step. The vast majority of spillover infections reach dead ends in the first human host.
This case serves as a sobering reminder that as H5N5 and other avian influenza subtypes continue to circulate in bird populations, opportunities for cross-species transmission will persist. Vigilant surveillance and research remain crucial for early detection of any changes in viral behaviour that might increase human risk.
