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Avian Influenza A (H5N1)

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Avian influenza is an infection caused by avian (bird) influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, avian influenza is very contagious and can make some domesticated birds, including chickens, ducks and turkeys, very sick and kill them. Usually, "avian influenza virus" refers to influenza A viruses found chiefly in birds, but infections can also occur in humans.

Unlike seasonal influenza, in which infection usually causes only mild respiratory symptoms in most healthy people, H5N1 infection may follow an unusually aggressive clinical course, with rapid deterioration and high fatality. Primary viral pneumonia and multi-organ failure have been common among people who have become ill with H5N1 influenza.

Who's at Risk?

The risk from avian influenza is generally low to most people, because the viruses do not usually infect humans. However, since 1997, there have been some confirmed cases of human infection from several subtypes of avian influenza. Most cases of avian influenza in humans have resulted from contact with infected poultry (e.g., domesticated chicken, ducks, and turkeys) or surfaces contaminated with secretion/excretions from infected birds.

The spread of avian influenza viruses from one ill person to another has been reported very rarely, and transmission has not been observed to continue beyond one person. Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could possibly infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. If the H5N1 virus were to gain the capacity to spread easily from person to person, an influenza pandemic could begin.

Can it Be Prevented?

There currently is no commercially available vaccine to protect humans against H5N1 virus that is being seen in Asia and Europe. However, vaccine development efforts are taking place. Research studies to test a vaccine to protect humans against H5N1 virus began in April 2005, and a series of clinical trials is under way.

Antivirals may help prevent infection in people at risk and lessen the impact of symptoms in those who become infected with influenza. It is unlikely that antivirals would substantially modify the course or contain the spread of an influenza pandemic.

The Bottom Line

Although the risk of humans contracting the avian influenza virus is low, certain precautions should be taken to reduce the risk of infection.

  • Americans are advised not to handle feather or bird-related products from countries experiencing outbreaks of the H5N1 virus.
  • Currently the Centers for Disease Control and Prevention advises travelers to countries with known outbreaks of H5N1 influenza to avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals.
  • In the event of an avian influenza pandemic, sick and exposed people should be treated with antivirals; sick people should be identified and quarantined in hospitals, homes, or other facilities; schools and workplaces should be closed as needed; and travel should be restricted.
  • In addition, people should protect themselves by staying away from people who are sick, staying home if they are sick; and washing their hands frequently with soap and water.

Case Examples

  1. A poultry farmer in Thailand notices that several of his chickens have died. He gets in touch with local authorities who contact the federal government. The World Health Organization is called in to investigate. They conclude that the chickens had the H5N1 virus. In an attempt to prevent the spread of the virus, all of the poultry farmers' chickens are killed.
  2. A young girl in California finds two dead birds in her backyard and informs her mother. Her mother is alarmed and immediately contacts the local health department. The birds are tested and the health deparment informs the woman that the cause of death was not bird flu. The mother is very relieved to hear the good news.
 
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  • Page last reviewed: February 2, 2011
  • Page last updated: February 2, 2011
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