Avian influenza is an infectious viral disease caused by avian influenza A viruses that primarily affects birds, but can sometimes infect humans and other animals.

What to know: 

• Naturally occurs in wild birds, especially waterfowl, and can spread to domestic poultry

• Some strains (such as H5N1, H5N2, or H7N9) can cause severe illness and high mortality in birds and humans

• Human infection is rare and usually occurs through direct contact with infected birds or contaminated environments

• Has the potential to pose a public health risk if a virus adapts for easy human-to-human spread

• Primarily infects wild birds and domestic poultry

• First identified in 1996 and has caused recurring outbreaks worldwide

• H5N1 among birds spreads through saliva, nasal secretions, feces, and contaminated environments
• H5N1 among humans usually spreads through direct contact with infected birds, dead birds, or contaminated surfaces
• In July 2025, the CDC announced it had ended its emergency response to the H5N1 avian flu.