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, and sometimes from birds to other animals. Rarely, the virus that causes bird flu can spread to a human. The virus spreads through the air, by handling a sick animal or direct contact with the bedding or stool of the animal. 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.