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The University of Maryland has released
full sequences from two isolates in Argentina. These sequences
have seasonal H and N genes circa 2003 which have reasserted with
pandemic H1N1 sequences to produce new reassortants with 6 gene
segments from pandemic H1N1 in association with seasonal H and N
from H1N1 or H1N2 circulating in humans in 2003.
The H1N1 sequence, A/swine/Argentina/CIP051-BsAs76/2009, was from Buenos Aires and collected in October, 2009. The H1N2 sequence, A/swine/Argentina/CIP051-StaFeN2/2010, was from Santa Fe and collected in May, 2010.
The number of swine sequences from countries south of the United States has been limited. Mexico reported a sequence from an early 2009 isolate which may have been a precursor of the pandemic H1N1 strain, while Argentina had released sequences from swine isolates thought to have originated from workers infected with pandemic H1N1. Chile has also released pandemic H1N1 isolated from turkeys.
However, the two recent sequences represent the first examples of reassortants with multiple pandemic genes reasserted with human seasonal genes (an earlier swine isolate in China had one pandemic H1N1 gene segment), which is a very dangerous situation since all six pandemic gene segments have been found in humans worldwide and the H and N genes were in humans in 2003. Therefore, these reassortants should be transmissible in humans and the H and N genes have not been widely reported in humans since 2003.
Since the H1 sequences are related to seasonal H1N1, it is unclear if current screening for H1 serotypes would distinguish these 2003 sequences from contemporary seasonal H1, which has been rare since the pandemic strain emerged, but is still being reported at low levels.
More information on seasonal H1 sub-typing activity against these 2003 sequences would be useful as would full sequencing of seasonal H1 isolates.