Avian influenza: implications for Australia

Avian influenza (AI) or ?bird flu? is a highly contagious viral infection of birds. Some AI viruses, called ?highly pathogenic avian influenza? (HPAI) viruses, can cause sudden high mortality (up to 100%) in domestic fowl (chickens). AI viruses are classified into subtypes on the basis of haemagglutinin (H) and neuraminidase (N) projections on their surface. There are 16 H and nine N types and, to date, all outbreaks of HPAI have been caused by H5 or H7 viruses.