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Paradigm Shift Intervention Monitoring
St Jude has released a full
set of sequences for an H1N2 isolate from Indiana, A/swine/Indiana/240218/2010,
collected on Feb 12, 2010. It has a pandemic H1N1 genetic background
with a human N2 from 1996 H3N2 and swine H1N1 and NP genes. This
isolate is part of a growing trend of reassortment between pandemic
H1N1 and various swine triple reassortants worldwide.
Moreover, the recent sequences involve H1N2, which is likely linked to the polymerase complex with human PB1 and avian PB2 / PA, which was initially found in H3N2 swine isolates from the 1990’s. Thus, the jump of pandemic H1N1 from humans back to swine may have selected for swine reassortants that included human N2, which was present in all of the H1N2 swine isolates.
All of these constellations were from 2010 isolates in Argentina, England, South Korea, and multiple locations in the United States (South Dakota, North Carolina, and Indiana).
On a related note, all reported trH3N2 infections in humans in the United States involved infections after the spread of pandemic H1N1, and all 2010 sequences have PB1 E618D, which may also represent a linkage between human adaptation and isolates with N2. There have been 5 reported cases in 2010, including two recent cases in Pennsylvania. The Pennsylvania situation remains unclear because of the large number of unsubtypable isolates, and recent weekly reports, which repeat warnings to physicians to be cognizant of the trH3N2 cases in Pennsylvania.