Avian flu: Frequently asked questions (Macon Telegraph) QUESTION: What is avian influenza? ANSWER: Avian influenza, or "bird flu," is a contagious disease of animals caused by viruses that normally infect only birds and, less commonly, pigs. Most strains of influenza originate in wild birds and never become deadly to birds or humans. The deadly strain of bird flu now spreading out of Asia is identified by scientists as strain H5N1. [News Source]