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2011 Ohio Swine H3N2v Matches With 2011 IN and PA Cases
Recombinomics Commentary 17:00
January 8, 2013

JCVI in association with Ohio State University has released full sets of sequences from isolates described in the EID report entitled “Subclinical Influenza Virus A Infections in Pigs Exhibited at Agricultural Fairs, Ohio, USA, 2009–2011.”  The 2011 sequences were from 6 agricultural fairs and, as reported, all 5 sets (see list below) of H3N2 sequences had an H1N1pdm09 M gene.  This distribution was markedly different than the 2011 and 2012 swine sequences released by the USDA, where most H3N2 sequences hade an M gene from triple reassortant swine lineages in North America.

More remarkable however, was the match of all of the Ohio swine sequences with the initial human isolates in 2011 (those from Indiana and Pennsylvania).  The USDA swine sequences from 2011 had matches with human cases, but most of the swine H3N2v sequences with an H1N1pdm09 M gene did not match human H3 and N2 lineages, and most that did match the human cases matched those from Maine, Iowa, or the latter sequence from Indiana, which were distinct from the initial case in Indiana (A/Indiana/08/2011( as well as the three cases in Pennsylvania (A/Pennsylvania/09/2011, A/Pennsylvania/10/2011, A/Pennsylvania/11/2012).

Like the USDA 2011 sequences, none of the 2011 Ohio swine sequences had the N2 lineage found at the West Virginia day care center in late 2011
(A/West Virginia/06/2011 and A/West Virginia/07/2011) or virtually all human H3N2 cases in 2012 (only three cases from Michigan had the N2 lineage which was common in H1N2, but the three cases from Michigan also had a PB1 gene found in human 2010 cases, which had E618D).

Although the above paper isolated H3N2v from asymptomatic at 5 of the 6 fairs, the ability of asymptomatic swine to transmit H3N2v to humans remains unclear.  There were no reported H3N2v human cases in Ohio in 2011 and the frequency of swine to human transmission in Pennsylvania was also unclear.  No H3N2v was isolated from swine at the Washington County fair, where three human cases were confirmed.  Further investigation of attendees identifies through a phone survey of 4-H families who presented at the fair identified 4 children with H3N2v antibodies and almost 80 additional attendees who had influenza-like illness.  Thus, these cases support human to human transmission between symptomatic cases, but don’t address transmission by asymptomatic swine or humans.

Interspecies transmission was clearly supported in Ohio fairs in 2012, as well as other agricultural fairs.  However, the direction of that transmission (human to swine or swine to human) remains unclear.  Virtually all 2012 human cases had an N2 that was distinct from the N2 frequently found in H1N2 swine (including asymptomatic swine at the 2011 Ohio fairs), and the N2 found in 2012 human cases was rarely found in swine collections made prior to the human cases identified at the 2012 fairs.

This discordance supports human to swine transmission, which is followed by swine to swine transmission and a significant increase in swine carrying the H3N2v found in humans.

H3N2 swine matches with 2011 human cases

A/swine/Ohio/11SW87/2011    August 5
A/swine/Ohio/11SW93/2011    August 5
A/swine/Ohio/11SW94/2011    August 5
A/swine/Ohio/11SW95/2011    August 5
A/swine/Ohio/11SW96/2011    August 5
A/swine/Ohio/11SW97/2011    August 5
A/swine/Ohio/11SW98/2011    August 5
A/swine/Ohio/11SW103/2011  August 5
A/swine/Ohio/11SW108/2011  August 5
A/swine/Ohio/11SW109/2011  August 5
A/swine/Ohio/11SW112/2011  August 5
A/swine/Ohio/11SW113/2011  August 5
A/swine/Ohio/11SW114/2011  August 5
A/swine/Ohio/11SW115/2011  August 5
A/swine/Ohio/11SW118/2011  August 5
A/swine/Ohio/11SW119/2011  August 5
A/swine/Ohio/11SW161/2011  August 8
A/swine/Ohio/11SW163/2011  August 8
A/swine/Ohio/11SW166/2011  August 8
A/swine/Ohio/11SW168/2011  August 8
A/swine/Ohio/11SW169/2011  August 8
A/swine/Ohio/11SW170/2011  August 8
A/swine/Ohio/11SW171/2011  August 8
A/swine/Ohio/11SW172/2011  August 8
A/swine/Ohio/11SW173/2011  August 8
A/swine/Ohio/11SW175/2011  August 8
A/swine/Ohio/11SW178/2011  August 8
A/swine/Ohio/11SW179/2011  August 8
A/swine/Ohio/11SW180/2011  August 8
A/swine/Ohio/11SW183/2011  August 8
A/swine/Ohio/11SW184/2011  August 8
A/swine/Ohio/11SW185/2011  August 8
A/swine/Ohio/11SW186/2011  August 8
A/swine/Ohio/11SW187/2011  August 8
A/swine/Ohio/11SW189/2011  August 8
A/swine/Ohio/11SW191/2011  August 8
A/swine/Ohio/11SW195/2011  August 8
A/swine/Ohio/11SW196/2011  August 8
A/swine/Ohio/11SW197/2011  August 8
A/swine/Ohio/11SW200/2011  August 8
A/swine/Ohio/11SW201/2011  August 12
A/swine/Ohio/11SW203/2011  August 12
A/swine/Ohio/11SW206/2011  August 12
A/swine/Ohio/11SW209/2011  August 12
A/swine/Ohio/11SW211/2011  August 12
A/swine/Ohio/11SW212/2011  August 12
A/swine/Ohio/11SW213/2011  August 12
A/swine/Ohio/11SW217/2011  August 12
A/swine/Ohio/11SW218/2011  August 12
A/swine/Ohio/11SW226/2011  August 18
A/swine/Ohio/11SW227/2011  August 18
A/swine/Ohio/11SW347/2011  August 19

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