The above comments from a recent paper entitled “Virulence and transmissibility of H1N2 influenza virus in ferrets imply the continuing threat of triple-reassortant swine viruses” describe the results of a transmission study using H1N2v. Like recent H5N1 studies , the virus under investigation was passed in ferrets and assayed for droplet transmission and pathological effects. The isolate of interest acquired non-synonymous changes in HA (D225G) and NA (S315N).

Prior studies in H1N1pdm09 have identified the association of HA D225G with severe and fatal human cases, which appears to also apply to the above H1N2v isolate from Korea. Although this isolate had genes found in North American swine, the virus has been transmitting in Korea for multiple years and the HA is most closely related to Korean H1N2v isolates.

Korea has not reported any human H1N2v cases. In contrast, the United States has reported six cases including four recent cases linked to the Minnesota State Fair. The first US case was in 2007, but last year there was a Minnesota case A/Minnesota/19/2011 which had no swine linkage. That isolates, like the first US H3N2v case, A/Kansas/13/2009, and all six cases in 2010, had an PB1 gene with E618D, which is present in all H1N1pdm09 cases (human and swine).

The four 2012 H1N2v cases have an M gene from H1N1pdm09 , which is also true for the H1N1v cases in 2011 (A/Wisconsin/28/2011) and 2012 (A/Missouri/12/2012), as well as all 2011 and 2012 H3N2v cases. Sequences from three of the H1N2v cases have been released (A/Minnesota/12/2012,

Although most of the TRSw viruses were moderately pathogenic, one [A/Swine/Korea/1204/2009; Sw/1204 (H1N2)] was virulent in ferrets, causing death within 10 d of inoculation, and was efficiently transmitted to naive contact ferrets via respiratory droplets.the Sw/1204 virus acquired mutations in hemagglutinin (HA) (Asp-225-Gly) and neuraminidase (NA) (Ser-315-Asn) proteins during the single ferret passage.