Bird flu, also called avian influenza, is a viral infection that can also infect humans and other animals. Read on to learn how it's diagnosed and. Avian influenza — known informally as avian flu or bird flu — refers to "influenza caused by viruses adapted to birds." The type with the greatest risk is highly History · Genetics · Subtypes · Spread. Bird flu, or avian flu, causes symptoms such as fever, cough, and sore throat. Learn about vaccination, transmission, treatment, prevention, and.