H5N6 is a subtype of avian influenza A virus, commonly known as bird flu. It primarily circulates among bird populations and can cause severe disease in infected birds. First identified in poultry in 2013, the virus has since spread globally among wild and domestic birds.
Understanding H5N6
H5N6 is classified as a highly pathogenic avian influenza (HPAI) virus, causing severe illness and high death rates in infected poultry. The “H” and “N” refer to hemagglutinin (HA) and neuraminidase (NA), two proteins on the virus’s surface that help it enter and exit host cells.
The virus’s genetic makeup results from reassortment, a process where different influenza viruses exchange genetic material when they co-infect the same host. This allows the virus to acquire new characteristics, influencing its ability to infect and cause disease.
Impact on Animal Populations
H5N6 outbreaks have a devastating impact on bird populations, especially domestic poultry such as chickens and ducks. The virus spreads rapidly within flocks, often leading to sudden, unexplained deaths. The mortality rate in infected chickens can be nearly 100% within 48 hours, causing significant losses for poultry farmers.
Wild migratory birds also play a role in the long-distance spread of H5N6, carrying the virus to new geographic regions. This widespread dissemination among both wild and domestic birds leads to substantial economic consequences for the poultry industry. These impacts include the direct loss of birds due to disease or preventative culling, as well as trade restrictions and reduced consumer demand. For instance, outbreaks in 2024 and 2025 led to the culling of millions of birds in the United States, incurring costs exceeding $1.4 billion.
Human Health Considerations
Human infection with H5N6 is considered rare, typically occurring through direct and prolonged contact with infected birds or environments contaminated with the virus. The virus enters a person’s body through the eyes, nose, mouth, or by inhalation. While human-to-human transmission has not been sustained, sporadic cases and small clusters can occur due to exposure.
Symptoms in human cases can range from mild, flu-like illness to severe respiratory infections, including pneumonia and acute respiratory distress syndrome (ARDS). The incubation period for human infection typically ranges from 1 to 13 days, with an average of 4.3 days. As of January 2025, 93 laboratory-confirmed cases of human infection with H5N6, including 57 deaths, have been reported to the World Health Organization in the Western Pacific Region since 2014, indicating a case fatality rate of approximately 61%.
Controlling the Spread
Controlling the spread of H5N6 involves a multi-faceted approach, starting with robust surveillance programs in both poultry farms and wild bird populations. This includes monitoring for symptoms, collecting samples for testing, and investigating exposure histories. Early detection through surveillance systems allows for more timely mitigation of the disease.
Biosecurity measures are also implemented to prevent the introduction and spread of the virus on farms. These measures include strict hygiene protocols, such as using disinfection booths for personnel and changing boots between sheds, and isolating flocks. When outbreaks occur, rapid culling of infected and exposed birds is performed to prevent wider dissemination of the virus. International cooperation and information sharing among health organizations are also integral to managing and preventing further spread.