Avian influenza (bird flu) is a viral disease of wild and domestic birds. 

The disease can vary from mild to severe, depending on the virus strain involved.  The current bird flu virus causing concern around the world is a severe strain (highly pathogenic) known as H5N1.  It has been found in parts of Asia, Europe, and Africa.  There is some concern that H5N1 may mutate so that it could also become widespread among humans. 

Currently, H5N1 is not present in the United States.