There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds.

“Human influenza virus” usually refers to those subtypes that spread widely among humans. There are three known A subtypes of influenza viruses (H1N1, H1N2, and H3N2) currently circulating

Chinese health care provider wearing double respiratory protection.

among humans. It is likely that some genetic parts of current human influenza A viruses came from birds originally. Influenza A viruses are constantly changing, and they might adapt over time to infect and spread among humans. Studies done in laboratories suggest that some of the prescription medicines approved in the United States for human influenza viruses should work in treating avian influenza infection in humans. However, influenza viruses can become resistant to these drugs, so these medications may not always work.

Influenza A (H5N1) virus – also called “H5N1 virus” – is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to them. H5N1 virus does not usually infect people, but infections with these viruses have occurred in humans. Most of these cases have resulted from people having direct or close contact with H5N1-infected poultry or H5N1-contaminated surfaces.

So far, the spread of H5N1 virus from person to person has been limited and has not continued beyond one person. Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could be able to 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 H5N1 virus were to gain the capacity to spread easily from person to person, an influenza pandemic (worldwide outbreak of disease) could begin.

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.

Ref: Avian Influenza (Bird Flu) - Facts -CDC

Patients with a history of travel within 10 days to a country with avian influenza activity and are hospitalized with a severe febrile respiratory illness, or are otherwise under evaluation for avian influenza, should be managed using isolation precautions identical to those recommended for patients with known Severe Acute Respiratory Syndrome (SARS). These include:

• Standard Precautions
  • Pay careful attention to hand hygiene before and after all patient contact or contact with items potentially contaminated with respiratory secretions.
• Contact Precautions
  • Use gloves and gown for all source contact.
  • Use dedicated equipment.
• Eye protection (i.e., goggles or face shields)
  • Wear when within 3 feet of the source.
• Airborne Precautions
  • Use a fit-tested respirator, at least as protective as a National Institute of Occupational Safety and Health (NIOSH)-approved N-95 filtering facepiece (i.e., disposable) respirator, when entering the room containing a source.
  
  
  Ref: Avian Influenza (Bird Flu)- Infection Control -CDC

• White House Policy for Preparing and Protecting Against Pandemic Flu (USA Gov)
• National Strategy for Pandemic Influenza (pdf)
• Health Officials Keep Close Watch on Bird Flu (NPR)
• U.S. Not Prepared for Bird Flu (ABC News)
• PandemicFlu.Gov (USA Gov)
• Africa 'not prepared' for bird flu (Malawi)
• Prevention of Avian Flu (UK)
• Protective Clothing for Avian Flu (pdf)