How are avian influenza viruses developed?
Wild birds are considered the reservoir for avian influenza viruses. Strains of influenza viruses are shed in feces and in the nasal, oral, and ocular secretions of wild birds. These strains do not become virulent unless they become established in large farm flocks of poultry, which become infected by contact with free-ranging waterfowl or feed, water, or soil contaminated with feces of wild waterfowl. Normally, wild birds do not carry or become ill from the virulent strains that circulate in poultry. The outbreak of H5N1 in Eurasia is unusual because wild birds have died from the disease, and migratory birds have been implicated in the spread of this virus.
