H3N2v Sequences Refute CDC Swine Exposure Message
September 6, 2012
Found in U.S. pigs in 2010 and humans in July 2011, this H3N2v virus appears to spread more easily from pigs to people than other variant influenza viruses. Most reported cases to date have occurred in people who are exhibiting or helping to exhibit pigs at fairs this season after close and prolonged contact with pigs. “So far more than 90 percent of cases have occurred in people who are exhibiting or helping to exhibit pigs, or who are family members of these people. That is why our message is so targeted,” says Finelli.
The above comments are from the August 31 CDC update on H3N2v and the comment that “this H3N2v virus” appearing first in humans in July 2011 clearly refers to the sub-clade represented by A/Indiana/08/2011, which has an H1N1pdm09 M gene. However, the claim that this sub-clade was found in pigs in 2010 is not supported by any public data, and is unlikely to be supported by any private data. Although the presence of the H1N1pdm09 M gene in H3N2 was found in swine in 2010, those isolates were easily distinguished from the 2011 sub-clade and have never been reported in human cases.
Moreover, the initial human H3N2v cases in 2011 were formed via reassortment between the dominant human H3N2v sub-clade in 2010 (which did not have an H1N1pdm09 M and contributed 5 gene segments (PB2, PA, HA, NP, NS) and swine H1N2, which contributed PB1, NA and an H1N1pdm09 M gene.