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WSN/33 Recombination and 1918 Pandemic
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The significance of WSN/33 in 2004 Korean swine might be best demonstrated on page 70 of the January 2005 edition of Scientific American. The article on the "Mystery of 1918" begins on page 64 and gives some detail on the pandemic as well as efforts that lead to the sequences acquired from fixed tissue samples from 1918 victims.
Attempts are made to explain the 1918 data using reassortment, which of course ends in hand waving about unknown viruses emerging from unknown species, but the real story is seen on page 70 which has a "flu family tree". Just below the 1918 isolates is "Iowa 1930" which is A/swine/Iowa/15/30(H1N1), a classical H1N1 swine isolated from Iowa in 1930. Just above the 1918 isolates is "Wilson Smith N 1933", which is A/WSN/33(H1N1). The 1918 pandemic strains were formed by recombination between swine sequences like "Iowa 1930" and human sequences like "Wilson Smith N 1933".
The human sequences, Wilson Smith N 1933 are WSN/33, the sequences in Korean swine in 2004.