Highly pathogenic Avian influenza A (H5N1) virus is an influenza A virus that occurs mainly in birds and can be deadly to them, especially for domestic poultry.
In human, Avian influenza A causes initial symptoms of high fever and an influenza-like illness with lower respiratory tract symptoms. Upper respiratory tract symptoms are present only sometimes. Diarrhea, abdominal pain, vomiting, pleuritic pain, and bleeding from nose and gums have also been reported early in the course of illness in some patients. Virologic diagnosis of influenza A H5N1 is confirmed by viral isolation, the detection of H5-specific RNA, or both methods.