Avian influenza is an infectious disease of birds caused by the influenza A virus. Birds are the hosts for most avian influenza viruses and a variety of influenza subtypes can be found in birds, particularly in water fowl and shore birds. Domestic poultry are especially vulnerable and the virus can rapidly cause epidemics in flocks.
Human infections with avian influenza are rare. However, some viruses, such as H5N1 or H7N9, have been associated with human disease.
The symptoms of avian influenza in humans vary considerably depending on the strain or subtype of the virus involved. Most infections take the form of a flu-like illness (fever, cough, body or muscle pain, sore throat, runny nose). Other symptoms can include conjunctivitis (red, sore and discharging eyes).