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Paradigm Shift Intervention Monitoring
Swine Solves H3N2pdm11 Pandemic Puzzle
Five of the eight gene segments of H3N2pdm11 (PB2, PA, HA, NP, NS) matched the dominant human trH3N2 sequences from 2010, represented by A/Pennsylvania/40/2010 and A/Wisconsin/12/2010, but the source for PB1 was unclear. The 2010 trH3N2 sequences had a PB1 that had evolved from the trH1N1 sequences from the Huron County Fair in Ohio, A/Ohio/01/2007 and A/Ohio/02/2007) and included the acquisition of E618D, but the H3N2pdm11 sequences had an earlier version, more closely related to H1N1 PB1 sequences, represented at Genbank by A/swine/OH/511445/2007 and A/swine/Ohio/24366/2007.
In addition to the PB1 sequence from A/swine/Ohio/FAH10-1/2010, OSU released two addition sets of sequences from trH1N1 swine, A/swine/Ohio/FAH2-1/2008 and A/swine/Ohio/FAH1-1/2007. The 2007 isolate emerged from the Huron County Fair sequences, as did the 2008 isolate, but the 2008 trH1N1 isolate, A/swine/Ohio/FAH2-1/2008, had a PB1 which was identical to the 2010 trH1N2 isolate, A/swine/Ohio/FAH10-1/2010, which fell onto a branch with earlier sequences, A/swine Kansas/77778/2007 and A/swine South Dakota/152B/2009 (which was H1N2 but had swine M gene). However, the Ohio sequences were much closer to the H3N2pdm11 PB1 found in the 10 human and 1 swine H3N2pdm11 isolates from 2011.
Thus, the 2010 Ohio trH1N2 isolate had acquired the 2008 trH1N1 PB1 sequence, which then created H3N2pdm11 through reassortment between the 2010 Ohio trH1N2 swine sequence and the 2010 human trH3N2 sequence. The adaptation to humans seen in the identities between A/Pennsylvania/40/2010 and A/Wisconsin/12/2010 was completed in the reassortant which acquired PB1, NA, and MP from A/swine/Ohio/FAH10-1/2010.