Highly Pathogenic Avian Influenza A (H5N1) Virus

Highly pathogenic avian influenza A (H5N1) virus – referred to as HPAI H5N1 and sometimes shortened to H5N1 – is a virus that occurs mainly in birds, is highly contagious among birds, and can be deadly to them, especially domestic poultry. Though relatively rare, sporadic human infections with this virus have occurred and caused serious illness and death.