Avian influenza is flu infection in birds. The disease(commonly known as bird flu) is of concern to humans, who have no immunity against it. The virus that causes this infection in birds can mutate to infect humans. Such mutation could start a deadly worldwide epidemic.

Avian influenza is an infectious disease of birds. Avian influenza viruses are rarely transmitted from birds to humans, and most of these cases have occurred from direct or close contact with infected poultry or contaminated surfaces. H5N1 virus does not usually infect people; however, a few cases of human-to-human spread of H5N1 virus have occurred.

Two main implications for human health from avian influenza are following:

• The first implication is of contracting a direct infection if the virus passes from the infected bird to humans, resulting in very severe disease. H5N1 has caused the largest number of cases of severe disease and death in humans. Primary viral pneumonia and multi-organ failure are common among people with avian influenza. The disease caused by H5N1 follows an unusually aggressive clinical course, with rapid deterioration and high fatality. More than half of those infected with the virus have died in the present outbreak.
• A second implication is that, the virus – if given enough opportunities – may mutate into a form that is extremely contagious for humans and spreads easily from person to person. Such a change could mark the start of a pandemic (a global outbreak).