Avian Influenza Carol J. Cardona, Extension Poultry Veterinarian, University of California, Davis Avian influenza is caused by type A influenza virus. More avian influenza viruses have been isolated from ducks than any other species although most free-flying birds may also be infected including shorebirds, gulls and other seabirds.
Waterfowl are more resistant to avian influenza than are domestic poultry.
Among domestic poultry species, turkeys are more commonly infected than are chickens. Transmission Waterfowl act as a reservoir of avian influenza virus by carrying the virus in their intestinal tract and shedding it in their feces. Avian influenza viruses are spread to susceptible birds through inhalation of influenza particles in nasal and respiratory secretions and from contact with the feces of infected birds. Signs of disease Signs of avian influenza are extremely variable. AI can also be manifest as respiratory, enteric, reproductive or nervous system disease.