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Absence of Utah / West Virginia H3N2v Constellation In Swine
Recombinomics Commentary 19:45
April 13, 2012

About half of the 12 infections in 2011 with H3N2v viruses like this one involved the patients being exposed to swine before becoming ill. The prevalence of this virus in swine is unknown, but it has been detected in U.S. swine through the United States Department of Agriculture’s (USDA) swine influenza surveillance program.

The above comment by the CDC with regard to 2011 sequences similar to the 2012 H3N2v sequences from the Utah case (A/Utah/10/2012) does not distinguish the clear difference in the constellation of the first 10 H3N2v human sequences in 2011 and the two sequences from West Virginia (A/West Virginia/06/2011 and A/West Virginia/07/2011), which have an N2 that matches the lineage found in North American swine H3N2 triple reassortant sequences, which is distinct from the N2 found in the first 10 human cases, which is from North American swine H1N2 triple reassortants.

The sequences from the first 10 cases in 2011 arose via reassortment with an H3N2v similar to the dominant sequence found in 2010 human H3N2v isolates (which contributed PB2, PA, HA, NP, NS), and an H1N2 sequence from Ohio, A/swine/Ohio/FAH10-1/2010, which contributed PB1, NA, MP.  This constellation was initially detected in human cases from Indiana and Pennsylvania in July and August.  It was subsequently identified in swine from New York and Iowa (A/swine/NY/A01104005/2011 and A/swine/Iowa/A01202640/2011) suggesting the swine infections were from humans.

Similarly, the constellation found in West Virginia was identified in two human isolates, but 22 additional contacts had influenza-like illness, strongly suggesting that these contacts were also infected with the novel constellation with an N2 from swine H3N2.

The release of sequences from the Utah case matches the two sequences from West Virginia, so once again the novel H3N2 constellation was found in humans prior to detection in swine, in spite of an enhanced USDA surveillance program.

Thus, the CDC comments above are misleading, because the H3N2v constellation found in West Virginia and Utah have never been reported in swine, and are likely transmitting via humans. The confirmed cases in West Virginia had no swine exposure, and the H3N2v in contacts was likely due to linkage to the Mineral County day care center, where the index case and confirmed contacts were students.

The finding of this novel constellation in West Virginia and Utah in the absence of any confirmed cases in swine, strongly supports human to human transmission and suggests more such human cases will be identified in 2012, as seasonal H3N2 levels decline.

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