Avian influenza-the bird flu - is a virus that infects birds, particularly wild birds such as ducks and geese, but can spread to domestic poultry, such as chickens and turkeys.here are numerous different strains of avian influenza; however, most do not cause illness in people. H5N1 is a strain of avian influenza, and is a concern among the scientific and medical community with regard to its potential to cause a pandemic. The H5N1 strain can infect birds, other animals and people.