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Avian influenza

Definition

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


Causes

Historically, avian influenza viruses infected pigs and mixed with pig influenza viruses. The viruses exchanged genetic information, which led to the formation of a new virus. This new virus could then infect humans and easily spread from person to person. Previous worldwide flu epidemics (pandemics) have started this way.

The first avian influenza virus to infect humans directly occurred in Hong Kong in 1997, during an avian flu epidemic on the island. This outbreak was linked to chickens and classified as avian influenza A (H5N1).

Since the Hong Kong outbreak, the bird flu virus has spread across Asia. In October 2005 it was discovered in poultry in Turkey and Romania.

The wider the area over which the avian flu virus spreads, the greater the chances of a worldwide outbreak. There is tremendous concern that H5N1 poses an enormous pandemic threat.

Farmers and other people working with poultry, as well as travelers visiting affected countries, have a higher risk for getting the bird flu. Handling an infected bird can cause infection. People who eat raw or undercooked poultry meat are also at an increased risk for avian influenza.

Highly infective avian flu viruses, such as H5N1, have been shown to survive in the environment for long periods of time. Infection may be spread simply by touching contaminated surfaces. Birds who recover from the flu can continue to shed the virus in their feces and saliva for as long as 10 days.

Health care workers and household contacts of patients with avian influenza may also be at an increased risk of the bird flu.


Symptoms

Symptoms of avian flu infection in humans depend on the strain of virus. Infection with the H5N1 virus in humans causes more classic flu-like symptoms, which might include:

  • Cough (dry or productive)
  • Diarrhea
  • Difficulty breathing
  • Fever greater than 100.4F (38C)
  • Headache
  • Malaise
  • Muscle aches
  • Runny nose
  • Sore throat

Treatment

Different types of avian flu virus may cause different symptoms. Therefore, treatment may vary.

In general, treatment with the antiviral medication oseltamivir (Tamiflu) or zanamivir (Relenza) may make the disease less severe -- if you start taking the medicine within 48 hours after your symptoms start.

Oseltamivir may also be prescribed for persons who live in the same house as those diagnosed with avian flu.

The virus that causes human avian flu appears to be resistant to the antiviral medicines amantadine and rimantadine. Therefore these medications should not be used if an H5N1 outbreak occurs.

People with severe infection may need to be placed on a breathing machine. Experts recommend that persons diagnosed with avian flu be put in isolation.

Doctors recommend that people get an influenza (flu) shot to reduce the chance of an avian flu virus mixing with a human flu virus, which would create a new virus that may easily spread.

The U.S. Food and Drug Administration has approved a vaccine to protect humans from the avian flu. Experts say the vaccine could be used if the current H5N1 virus starts spreading between people.


Prognosis

The outlook depends on the severity of infection and the type of avian influenza virus that caused it. The current death rate for patients with confirmed H5N1 infection is more than 50%.

The H7N7 avian flu outbreak in the Netherlands resulted in 89 confirmed human cases but only one death. The avian flu virus H9N2 infected three children in Asia; all of them recovered.


Prevention

Travelers should avoid visits to live-bird markets in areas with an avian flu outbreak. People who work with birds who might be infected should use protective clothing and special breathing masks. Avoiding undercooked or uncooked meat reduces the risk of exposure to avian flu and other foodborne diseases.