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Commentary
trH1N1
Transmission In South Dakota Prior to 2009 Pandemic
Recombinomics Commentary 14:11
September 16, 2011
Of 99 event pig-exposed students, 72 (73%) participated in the investigation, and 42 (42%) provided serum samples, of whom 17 (40%) were seropositive and 5 (12%) met case criteria. Of 9 students exposed to other pigs, 2 (22%) were seropositive. Of 8 index case-exposed persons and 10 without exposures, none were seropositive. Pig-exposed persons were more likely to be seropositive than persons without pig exposure (37% vs 0%, P < .01).
The results above are from a recent 2011 paper entitled, “A Pre-Pandemic Outbreak of Triple-Reassortant Swine Influenza Virus Infection Among University Students, South Dakota, 2008”, which demonstrate the ease of transmission of a trH1N1 in late 2008 (40% of tested samples from students with swine exposure had trH1N1 antibodies), prior to the 2009 H1N1 pandemic. These results were similar to the data from the Huron County Fair in Ohio in 2007 where trH1N1 was isolated (A/Ohio/02/2007 and A/Ohio/01/2007) from a presenter (10F) and her father (36M), respectively, and two dozen fair attendees had flu-like symptoms. These events signal efficient transmission of trH1N1 to humans.
Sequences from the H1N1 isolate, A/South Dakota/03/2008, from the student (19M) have been released at GISAID and GenBank and these sequences create a clustering with other human cases identified prior to the 2009, including several isolates from Iowa (most closely related HA sequence, , A/Iowa/05/2007, was from a 2M, who lived on a farm and was in close proximity to swine. The clustering signaled evolution toward human transmission.
Remarkably, the M gene from this case was related to clustering trH3N2 sequences from 2010, highlighting the importance of the M gene in transmission to humans, raising concerns that the acquisition of the M gene from the 2009 H1N1 signals the significant acceleration of the trH3N2 pandemic.
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