Avian influenza (bird flu) refers to the disease found in bird species caused by influenza (flu) Type A viruses. The disease varies in severity, i.e., low pathogenicity (LPAI), no symptoms or death to highly pathogenic (HPAI), highly infectious, high death rates in birds, and sometimes in humans, other mammals, and domestic animals. For more information, read the Avian Influenza Virus Health Alert.