The Influenza Division at the Centers for Disease Control (CDC) reported in Science that the genes found in the H1N1 (Swine flu) genome have been circulating in the environment for an extended period of time but have now combined in a new way to cause infection.
By sequencing full or partial genomes of isolates of the virus found in Mexico and the United States, the researchers found combinations of 8 influenza gene segments that had not been previously described in either human or swine viruses.
The scientists found that all segments had originated in avian (bird) hosts and then entered into the swine (pig) population sometime between 1918 and 1998. Two of the segments were derived from Eurasian swine viruses that had not been detected previously outside Eurasia. The other six segments included DNA from human, swine and avian sources that had been circulating since 1998.
Where and how these various segments came together is not clear. They do know that the event lead to the genesis of the novel H1N1 virus that has antigenic properties that are distinct from seasonal human influenza but are similar to other swine-origin influenza viruses.
The CDC reports 6764 probable and confirmed cases of H1N1 in the United States. There have been 10 fatalities to date in the U.S.
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