Avian influenza

 

Avian influenza

Avian influenza, commonly known as bird flu, is a contagious viral disease caused by type A influenza viruses that primarily infect birds and occasionally mammals, including humans. It remains a major global zoonotic concern due to its potential to mutate and trigger severe outbreaks or pandemics.

Key facts

• Causative agent: Avian influenza A viruses (e.g., H5N1, H5N6, H7N9)

• Primary hosts: Wild waterfowl and domestic poultry

• Transmission to humans: Direct or close contact with infected birds or contaminated environments

• Current risk (2025–26): Low for the general public, according to CDC and WHO

• First major human cases: 1997 Hong Kong H5N1 outbreak

Virology and variants

Avian influenza viruses are classified by combinations of hemagglutinin (H) and neuraminidase (N) surface proteins. Highly pathogenic avian influenza (HPAI) forms such as H5N1 and H7N9 cause severe disease and high mortality in birds and, occasionally, humans. Low pathogenic forms (LPAI) usually produce mild or no symptoms in birds but can evolve into HPAI through mutation

Transmission and human infection

The viruses spread among birds through saliva, nasal secretions, and feces. Human infections occur mostly after unprotected contact with infected poultry, wild birds, or contaminated materials such as litter or water. Rare transmission has also been linked to exposure to infected mammals, including dairy cattle in the U.S. Limited human-to-human transmission has been reported but not sustained.

Symptoms and severity

Human illness ranges from mild conjunctivitis and fever to severe pneumonia, acute respiratory distress, and multiorgan failure. Symptoms typically appear within 1–10 days after exposure. The fatality rate for H5N1 infections historically exceeded 50% globally.

Prevention and control

Preventive measures emphasize avoiding contact with sick or dead birds, practicing hand hygiene, cooking poultry and eggs thoroughly, and using personal protective equipment for animal handlers. Seasonal flu vaccination is advised to prevent coinfection with avian and human influenza viruses. No commercial human vaccine against avian influenza is currently recommended, though candidate vaccines exist for pandemic preparedness.

Global situation and response

Avian influenza outbreaks in poultry and wild birds are widespread, with recent detections of H5N1 clade 2.3.4.4b across continents. National health authorities—including the CDC, WHO, and EMA—maintain surveillance, preparedness, and vaccine development programs under a One Health framework linking human, animal, and environmental health.