Avian (Bird) Flu: An Overview
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 them. However, some domesticated birds, including chickens, ducks, and turkeys, can become infected with the avian flu virus and die.
Avian (Bird) Flu: H5N1 in Animals
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. Avian (bird)
flu symptoms in birds and other animals vary, but virulent strains can cause death within a few days.
Avian (Bird) Flu: H5N1 in Humans
Avian (bird) flu H5N1 in humans is currently very limited and not a
pandemic. Human H5N1 influenza infection was first recognized in 1997, when this virus infected 18 people in Hong Kong, causing 6 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 of the avian flu virus.
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 of avian (bird) flu. 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.
Pandemic Versus Seasonal Outbreak of Avian (Bird) Flu
Scientists are worried that avian (bird) flu could become an
influenza pandemic. An
influenza pandemic is different from a seasonal outbreak or "epidemic" of influenza. Seasonal outbreaks are caused by subtypes of influenza viruses that already circulate among people, whereas influenza pandemic outbreaks are caused by new subtypes, by subtypes that have never circulated among people, or by subtypes that have not circulated among people for a long time. Past influenza pandemics have led to high levels of illness, death, social disruption, and economic loss.
Symptoms of Avian (Bird) Flu
The reported symptoms of avian (bird) flu in humans have ranged from typical influenza-like symptoms (fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), acute respiratory distress, viral pneumonia, and other severe, life-threatening complications.
Prevention and Treatment of Avian (Bird) Flu
Vaccines to protect humans against
H5N1 avian (bird) flu are currently under development. In addition, research is underway on methods to make large quantities of avian (bird)
flu vaccine more quickly. So far, research suggests that two antiviral medicines, oseltamavir (
Tamiflu®) and zanamavir (
Relenza®), may be useful treatments for H5N1 avian (bird) flu. However, H5N1 viruses are generally resistant to two other available antiviral medications,
amantadine and
rimantadine, which cannot be used to treat avian (bird) flu.
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