Influenza A virus subtype H1N1 - Wikipedia, the free encyclopedia

Influenza A virus subtype H1N1 - Wikipedia, the free encyclopedia: "H1N1 is a subtype of the species Influenza A virus. The 'H' refers to the Hemagglutinin protein, and the 'N' refers to the Neuraminidase protein. H1N1 has mutated into various strains including the Spanish Flu strain (now extinct in the wild), mild human flu strains, endemic pig strains, and various strains found in birds. A variant of H1N1 was responsible for the Spanish flu pandemic that killed some 50 million to 100 million people worldwide from 1918 to 1919.[1] A different variant exists in pig populations.

'When he compared the 1918 virus with today's human flu viruses, Dr. [Jeffery] Taubenberger noticed that it had alterations in just 25 to 30 of the virus's 4,400 amino acids. Those few changes turned a bird virus into a killer that could spread from person to person.'[2]

Low pathogenic H1N1 strains still exist in the wild today, causing roughly half of all flu infections in 2006.[3]

The New York case has been confirmed as Influenza A Virus, which meets the Centers for Disease Control and Prevention (or CDC) definition of a probable case of swine flu. Tests are still underway to determine if this flu virus is the new strain of H1N1. Two cases have been confirmed in Kansas. Kansas state health officials confirmed two cases of swine flu in Kansas on 25th April 2009, just minutes after New York health officials said they had eight probable cases.

http://www.cdc.gov/flu/weekly/