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Avian (bird) flu is an infection caused by influenza viruses that occur naturally in birds. Symptoms in humans have ranged from common flu-like symptoms (fever, cough, sore throat, and muscle aches) to eye infections, acute respiratory distress, viral pneumonia, and other life-threatening complications. Vaccines to protect humans against H5N1 bird flu are currently under development.
Avian influenza -- commonly called "bird flu" or "avian flu" -- is an infection caused by an influenza virus (avian flu virus) that occurs naturally in birds. Wild birds can carry the avian flu virus, but usually do not get sick from it. However, some domesticated birds, including chickens, ducks, and turkeys, can become infected with the avian flu virus and die.
One strain of avian (bird) flu, the H5N1 virus, is endemic in much of Asia and has recently spread into Europe. Avian H5N1 infections have recently killed poultry and other birds in a number of countries. Strains of avian H5N1 influenza may infect various types of animals, including wild birds, pigs, and tigers. Symptoms in birds and other animals vary, but virulent strains can cause death within a few days.
Avian (Bird) Flu in Humans
Avian (bird) flu H5N1 in humans is currently limited and not a pandemic. Human H5N1 influenza infection was first recognized in 1997, when this virus infected 18 people in Hong Kong, causing six deaths. Since 2003, more than 100 human H5N1 flu cases have been diagnosed in Thailand, Vietnam, Cambodia, Indonesia, and China. Of those cases, more than half have died as a result.
Currently, close contact with infected poultry has been the primary source of human infection for avian (bird) flu. Though rare, there have been isolated reports of human-to-human transmission. Genetic studies confirm that the influenza A virus H5N1 mutates rapidly, which means that should it adapt to allow easy human-to-human transmission, a pandemic could ensue. At this time, it is uncertain whether the currently circulating H5N1 virus will lead to a global disease outbreak in humans -- a pandemic.