Avian influenza (AI) is an infectious viral disease caused by strains of influenza A virus. It mainly affects birds. Waterfowl such as ducks, swans and geese (Anseriformes) and gulls, terns and shorebirds (Charadiformes) are the natural reservoirs for avian influenza A viruses.
Since 2020, a new strain of avian influenza called HPAI H5N1 clade 2.3.4.4b (known as H5 avian influenza or H5 bird flu) has been causing unprecedented outbreaks of disease in wild birds, wild mammals and some domesticated mammals across every continent except Australia.
