Avian Flu

H5N1 is a subtype of the species called avian influenza virus (bird flu). Avian flu is a disease and avian flu virus is a species. The avian flu virus subtypes are labeled according to an H number and an N number.

The avian influenza subtypes that have been confirmed in humans, ordered by the number of known human deaths, are:

• H1N1 caused "Spanish Flu",
• H2N2 caused "Asian Flu",
• H3N2 caused "Hong Kong Flu",
• H5N1 is the current pandemic threat,
• H7N7 has unusual zoonotic potential,
• H1N2 is currently endemic in humans and pigs,
• H9N2, H7N2, H7N3, H10N7.
  

The annual flu (also called "seasonal flu" or "human flu") kills an estimated 36,000 people in the United States each year. The dominant strain of annual flu virus in January 2006 was H3N2 which is now resistant to the standard antiviral drugs amantadine and rimantadine.

Avian influenza virus H3N2 is endemic in pigs ("swine flu") in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment.) with H5N1, swapping genes and mutating into a form which can pass easily among humans. A combination of these two subtypes of the species known as the avian flu virus in a country like China is a worst case scenerio.