Published Date: 2012-04-07 13:21:29
Subject: PRO/AH> Influenza (25): H3N2v, pathogenesis & transmission
Archive Number: 20120407.1093271
INFLUENZA (25): H3N2V, PATHOGENESIS AND TRANSMISSIBILITY
A ProMED-mail posthttp://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseaseshttp://www.isid.org
Date: Fri 6 Apr 2012
Soirce: CIDRAP News [edited]http://www.cidrap.umn.edu/cidrap/conten ... an-jw.html
No increased virulence in novel H3N2 viruses, related swine strains
US researchers say they found no evidence of increased virulence in a novel reassortant H3N2 influenza virus (H3N2v) from one of the 12 human cases identified in the United States last year or in several related H3N2 viruses from pigs. The 12 H3N2v infections detected last summer and fall involved swine-origin H3N2 strains that included the M (matrix) gene from the pandemic 2009 H1N1 (pH1N1) virus. The report in the Journal of Virology [see Abstract reproduced below] says that swine H3N2 viruses with triple-reassortant internal genes (H3N2-TRIG) have been widespread in the United States since 1998. Transmission of the pH1N1 virus from humans to pigs resulted in reassortant H3N2 viruses that included genetic elements from pH1N1, which the authors call rH3N2p. They say their genome analysis of H3N2 viruses collected from swine from 2009 to 2011 revealed six different rH3N2p genotypes in the US swine population, all of which include the M gene from pH1N1. The team compared the pathogenic, transmission, genetic, and antigenic properties of a human H3N2v isolate and two swine H3N2 isolates -- an H3N2-TRIG and an rH3N2p. They found that in pigs, the H3N2v and rH3N2p viruses were no more virulent than the background H3N2-TRIG strain, with most infected pigs showing mild illness. The authors also found that some recent rH3N2p isolates seem to be forming a separate genetic cluster with the human H3N2v strain. The findings, they say, add to the evidence that influenza A viruses readily pass between humans and animals and that pigs play a role in generating reassortant viruses. "Continued monitoring of these H3N2 viruses is necessary to evaluate evolution and potential loss of population immunity in swine and humans," the report concludes.
[Abstract from Journal of Virology manuscript:
Pathogenicity and transmission in pigs of the novel A(H3N2)v influenza virus isolated from humans and characterization of swine H3N2 viruses isolated in 2010-2011.
By Pravina Kitikoon and 10 others. J.Virol., online ahead of publication at: http://jvi.asm.org/content/early/2012/0 ... 2.abstract
"Swine influenza virus (SIV) H3N2 with triple reassorted internal genes (TRIG) has been enzootic in U.S. since 1998. Transmission of the 2009 pandemic H1N1 (pH1N1) virus to pigs in the U.S. was followed by reassortment with endemic SIV, resulting in reassorted viruses that include the novel H3N2 genotypes (rH3N2p).
Between July-December 2011, 12 cases of human infections with swine-lineage H3N2 viruses containing the pandemic matrix (pM) gene (A(H3N2)v) were detected. [see ProMED-mail archived reports listed below]. Whole genome analysis of H3N2 viruses isolated from pigs from 2009-2011 sequenced in this study and other available H3N2 sequences showed six different rH3N2p genotypes present in the U.S. swine population since 2009. The presence of the pM gene was a common feature among all rH3N2p genotypes, but no specific genotype appeared to predominate in the swine population.
We compared the pathogenic, transmission, genetic, and antigenic properties of a human A(H3N2)v isolate and two swine H3N2 isolates, H3N2-TRIG and rH3N2p. Our _in vivo_ study detected no increased virulence in A(H3N2)v or rH3N2p viruses compared to endemic H3N2-TRIG virus. Antibodies to cluster IV H3N2-TRIG and rH3N2p viruses had reduced cross-reactivity to A(H3N2)v compared to other cluster IV H3N2-TRIG and rH3N2p viruses.
Genetic analysis of the haemagglutinin gene indicated that although rH3N2p and A(H3N2)v are related to cluster IV of H3N2-TRIG, some recent rH3N2p isolates appeared to be forming a separate cluster along with the human isolates of A(H3N2)v.
Continued monitoring of these H3N2 viruses is necessary to evaluate evolution and potential loss of population immunity in swine and humans."
These findings discount the likelihood that increased transmissibility and/or virulence is a property of the H3N2 recombinant viruses recovered from children in 2011, and also warn against simplistic explanations for the evolution of epidemic influenza viruses. - Mod.CP]
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