Avian influenza

Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A virus, which is enzootic (continually present) in many bird populations.

Symptoms of avian influenza vary according to both the strain of virus underlying the infection, and on the species of bird or mammal affected. Classification of a virus strain as either low pathogenic avian influenza (LPAI) or high pathogenic avian influenza (HPAI) is based on the severity of symptoms in domestic chickens and does not predict severity of symptoms in other species. Chickens infected with LPAI display mild symptoms or are asymptomatic, whereas HPAI causes serious breathing difficulties, significant drop in egg production, and sudden death. Domestic poultry may potentially be protected from specific strains of the virus by vaccination.

Humans and other mammals can only become infected with avian influenza after prolonged close contact with infected birds. In mammals including humans, infection with avian influenza (whether LPAI or HPAI) is rare. Symptoms of infection vary from mild to severe, including fever, diarrhoea, and cough.

Influenza A virus is shed in the saliva, mucous, and feces of infected birds; other infected animals may shed bird flu viruses in respiratory secretions and other body fluids (e.g., cow milk). The virus can spread rapidly through poultry flocks and among wild birds. A particularly virulent strain, influenza A virus subtype H5N1 (A/H5N1) has the potential to decimate domesticated poultry stocks and an estimated half a billion farmed birds have been slaughtered in efforts to contain the virus.

Avian flu or bird flu mainly affects chickens, geese, pigeons, quail and similar domesticated birds. There is also evidence that wild bird populations serve as reservoirs for the virus. The virus can be transmitted directly from fowl to humans leading to serious illness and death. Two characteristics of "bird flu" make it potentially pandemic: (1) it represents a new strain of influenza and (2) people have no natural immune resistance to it. To date it is unproven whether the virus can be transmitted person to person or is solely contracted from direct contact with diseased fowl. The human symptoms of "bird flu" are classic for influenza; sore throat, fever and muscle ache, but can become deadly in the young, elderly or infirm.