Avian influenza is an influenza A virus infection of poultry that affects primarily the respiratory tract, but in its highly pathogenic form it becomes a systemic, multi‑organ disease with high mortality. LPAI (low pathogenic) strains (e.g. H9N2) remain largely confined to the respiratory and intestinal tracts, whilst HPAI (high pathogenic) strains (H5, H7) spread throughout the body and cause severe lesions and death.
