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 mutate (change) to easily infect humans. Such mutation can start a deadly worldwide epidemic.

Alternative Names

Bird flu; H5N1

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 flu pandemics (worldwide epidemics) 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, and in October 2005 was discovered in poultry in Turkey and Romania. So far, hundreds of people have been infected by H5N1. Many people have died.

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, and 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 particular strain of virus. In case of the H5N1 virus, infection in humans causes more classic flu-like symptoms, which might include:

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

Exams and Tests

If you think you have been exposed to avian influenza, call your health care provider before your visit. This will give the staff a chance to take proper precautions that will protect them and other patients.

In February 2006, the U.S. Food & Drug Administration approved a new, faster test for diagnosing strains of bird flu in people suspected of having the virus. The test is called the Influenza A/H5 (Asian lineage) Virus Real-time RT-PCR Primer and Probe Set. The test gives preliminary results within 4 hours. Older tests required 2 to 3 days.

Your doctor might also perform the following tests:

• Chest x-ray  
• Nasopharyngeal culture  
• Blood differential
• Auscultation (to detect abnormal breath sounds)

Other tests may be done to look at the functions of your heart, kidneys, and liver.

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 cannot 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.

Outlook (Prognosis)

Prognosis 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. An avian flu virus designates H9N2 infected 3 children in Asia; all three recovered.

Possible Complications

Pneumonia  and acute respiratory distress are seen with H5N1 infections. Infection with this virus may also lead to sepsis and organ failure.

When to Contact a Medical Professional

Call your health care provider if you develop flu-like symptoms within 10 days of handling infected birds or traveling to an area with a known avian flu outbreak.

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 food borne diseases

US Food and Drug Administration. FDA Approves First U.S. Vaccine for Humans Against the Avian Influenza Virus H5N1. Rockville, MD: National Press Office; April 17, 2007. Release P07-68

US Centers for Disease Control and Prevention. New Laboratory Assay for Diagnostic Testing of Avian Influenza A/H5 (Asian Lineage). MMWR. February 3, 2006/55(Early Release);1.

World Health Organization. Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO. Geneva, Switzerland: World Health Organization; 2006.

Beigel JH, Farrar J, Han AM, et al. Avian Influenza A (H5N1) Infection in Humans. N Engl J Med. 2005;353:1374-85.