An infection of the nose, throat and lungs caused by a virus. Bird flu also is called avian flu or avian influenza.

Bird flu spreads naturally between wild birds. Rarely, the virus that causes bird flu can spread to a human. The virus spreads through the air, by handling a sick bird or by touching a surface contaminated by a sick bird. Bird flu infections in humans are rare. Most people recover from bird flu, but it can be deadly.

Bird flu symptoms can be similar to a common flu, including eye redness, fever, muscle aches, headache, tiredness, and runny or stuffy nose. People also may vomit or have diarrhea. Very serious illness can cause fluid to build up in the lungs. This causes serious problems with breathing that is treated in the hospital.

People with a likely or confirmed bird flu infection can be treated with antiviral medicine.