Influenza A virus causes influenza in birds and some mammals, and is the only species of the genus "Alphainfluenzavirus" of the virus family "Orthomyxoviridae". Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans. Occasionally, viruses are transmitted from wild aquatic birds to domestic poultry, and this may cause an outbreak or give rise to human influenza pandemics.