Genetic characterization of H3N2 influenza viruses isolated from pigs in North America, 1977–1999: evidence for wholly human and reassortant virus genotypes

Abstract

Since 1998, H3N2 viruses have caused epizootics of respiratory disease in pigs throughout the major swine production regions of the U.S. These outbreaks are remarkable because swine influenza in North America had previously been caused almost exclusively by H1N1 viruses. We sequenced the full-length protein coding regions of all eight RNA segments from four H3N2 viruses that we isolated from pigs in the Midwestern U.S. between March 1998 and March 1999, as well as from H3N2 viruses recovered from a piglet in Canada in January 1997 and from a pig in Colorado in 1977. Phylogenetic analyses demonstrated that the 1977 Colorado and 1997 Ontario isolates are wholly human influenza viruses. However, the viruses isolated since 1998 from pigs in the Midwestern U.S. are reassortant viruses containing hemagglutinin, neuraminidase and PB1 polymerase genes from human influenza viruses, matrix, non-structural and nucleoprotein genes from classical swine viruses, and PA and PB2 polymerase genes from avian viruses. The HA proteins of the Midwestern reassortant swine viruses can be differentiated from those of the 1995 lineage of human H3 viruses by 12 amino acid mutations in HA1. In contrast, the Sw/ONT/97 virus, which did not spread from pig-to-pig, lacks 11 of these changes.

Pandemic influenza planning: Shouldn’t swine and poultry workers be included?

“…In recent years a number of such novel viruses have emerged to cause epidemics among swine. [22][23][24]. It is important to note that while avian influenza viruses are rarely detected among swine, swine influenza viruses are rather commonly detected among domestic avian species.…”

Human Case of Swine Influenza A (H1N1) Triple Reassortant Virus Infection, Wisconsin

“…Triple reassortant swine infl uenza viruses (containing genes derived from human, swine, and avian infl uenza A viruses) have been isolated from swine in the United States since 1998 (9,10), and human infections with swine reassortant viruses have been documented (11)(12)(13). We report a case of respiratory illness in an adolescent boy associated with swine infl uenza A (H1N1) triple reassortant virus infection.…”

Isolation of novel triple‐reassortant swine H3N2 influenza viruses possessing the hemagglutinin and neuraminidase genes of a seasonal influenza virus in Vietnam in 2010

“…The Vietnamese isolates lost five potential glycosylation sites at positions 8, 122, 133, 144, and 165 that are conserved among human isolates (Table 3). 13 Among them, glycosylation sites at positions 122 and 133 are located in the vicinity of the receptor‐binding site that is conserved in humans but not in swine isolates 14 . The loss of the glycosylation sites at those positions could affect receptor recognition of the SIVs.…”