Avian Influenza, also known as ‘avian flu’ or ‘bird flu’ is an infection- usually of wild birds- but sometimes also of commercial or domestic poultry.  Water birds are the natural host of Avian Influenza. Avian influenza viruses are within the group of ‘influenza A viruses’ and are classified into subtypes according to two proteins found on the surface of the virus: haemagglutinin (H) and neuraminidase (N).