Bird flu, or avian influenza, is a type of influenza virus that spreads among birds, including wild and domesticated birds. In rare cases, it can affect humans. Human infections with bird flu viruses can happen when the virus gets into a persons eyes, nose, or mouth, or is inhaled. This can happen when the virus is in the air (in droplets or possibly dust) and a person breathes it in, or possibly when a person touches something that has the virus on it and then touches their mouth, eyes, or nose. The symptoms of bird flu in humans can range from no symptoms or mild illness, such as eye infection or mild flu-like upper respiratory symptoms, to severe disease, such as pneumonia, that can result in death. The reported signs and symptoms of bird flu virus infections in humans have included fever, cough, sore throat, headache, muscle aches, and shortness of breath or difficulty breathing.

Human infections with bird flu viruses have occurred most often after close or lengthy unprotected contact with infected birds or surfaces contaminated with bird flu viruses. However, some infections have been identified where direct contact with infected birds or their environment was not known to have occurred. The spread of bird flu viruses from one infected person to a close contact is very rare, and when it has happened, it has not led to continued spread among people.

It is important to note that there is no clear evidence that the virus can be transmitted from human to human, but scientists are concerned that the bird flu virus may combine with a human flu virus and mutate, which may make transmission between humans possible. The risk of human infection with bird flu viruses is generally low, but people who have regular contact with poultry or wild birds are most at risk. To prevent bird flu, people should avoid direct contact with wild birds, avoid unprotected contact with domestic birds that look sick or have died, and not touch surfaces that may be contaminated with saliva, mucous, or feces from wild or domestic birds.