H3N2v NA N234D Spread To Minnesota
August 29, 2012
The recently released H3N2v sequence from Minnesota, A/Minnesota/11/2012, has NA N234D, which abolishes the glycosylation site and raises concerns that this change may represent adaptation toward more efficient human transmission, as was reported in three H5N1 transmission studies which identified the loss of an HA glycosylation site (N158D) as a critical change in adaptation to human infections.
The NA sequence in Minnesota is identical to eight sequences from Butler County in Ohio (A/Ohio/13/2012, A/Ohio/14/2012, A/Ohio/15/2012, A/Ohio/16/2012, A/Ohio/17/2012, A/Ohio/18/2012, A/Ohio/20/2012, and A/Ohio/24/2012), as well as the two full sequences from LaPorte County in Indiana (A/Indiana/07/2012 and A/Indiana/09/2012) and presumably the other two LaPorte cases (A/Indiana/06/2012 and A/Indiana/08/2012), which have yielded partial sequences that are identical to the two full sequences.
The identity in the NA sequences from isolates in three states highlights the similarities in the H3N2v sequences from July and August isolates from 7 states (Hawaii, Indiana, Ohio, Maryland, Minnesota, Pennsylvania, and Wisconsin). All match the sub-clade initially detected at a West Virginia day care center which had extensive human to human transmission in contacts (A/West Virginia/07/2011) and index case (A/West Virginia/06/2011) with no swine exposure. This sub-clade was also identified in Utah (A/Utah/10/2012) in late March.
However, the recent cases represent a clonal expansion with the closely related sequences in all 8 gene segments. All map to the same branch in phylogenetic analysis and 7 of the 8 branches (all except NP) have evolved directly from the West Virginia sequences.