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Comparative Study
. 2003 May;41(5):1936-41.
doi: 10.1128/JCM.41.5.1936-1941.2003.

Comparison of the pathogenesis of two genetically different H3N2 influenza A viruses in pigs

Gabriele A Landolt  1 , Alexander I Karasin, Lynette Phillips, Christopher W Olsen
Affiliations
Comparative Study

Comparison of the pathogenesis of two genetically different H3N2 influenza A viruses in pigs

Gabriele A Landolt et al. J Clin Microbiol. 2003 May.

Abstract

In 1997 and 1998, H3N2 influenza A viruses emerged among pigs in North America. Genetic analyses of the H3N2 isolates demonstrated that they had distinctly different genotypes. The most commonly isolated viruses in the United States have a triple-reassortant genotype, with the hemagglutinin, neuraminidase, and PB1 polymerase genes being of human influenza virus origin, the nucleoprotein, matrix, and nonstructural genes being of classical swine influenza virus origin, and the PA and PB2 polymerase genes being of avian influenza virus origin. In contrast, a wholly human H3N2 virus was isolated from a single baby pig in Ontario, Canada, in 1997, but it did not spread within the swine population. Genetic differences between this wholly human virus and the triple-reassortant viruses may affect their replication efficiencies in pigs. In the present study we compared the pathogenicities and replication kinetics of the wholly human virus and a triple-reassortant virus in 7-week-old pigs that were infected intranasally with 2 x 10(3) to 2 x 10(6) 50% tissue culture infective doses of virus. Our results demonstrate that the wholly human virus replicated to significantly lower titers and that the onset of virus shedding was delayed compared to the replication titers and the time of onset of virus shedding in triple-reassortant viruses. In addition, infection with the triple-reassortant virus was associated with moderate to severe gross pathological and histological pulmonary lesions, while infection with the wholly human virus induced only mild pulmonary changes.

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Figures

FIG. 1.
FIG. 1.
Group means ± SEMs of nasal virus shedding from pigs infected with either Sw/MN (•) or Sw/ONT (○) from the day of inoculation (day 0) to day 7 after inoculation. (A) Pigs infected with 2 × 103 TCID50s of virus; (B) pigs infected with 2 × 104 TCID50s of virus; (C) pigs infected with 2 × 105 TCID50s of virus; (D) pigs infected with 2 × 106 TCID50s of virus. Control animals did not shed virus at any point during the experiment and are not represented in the graphs. *, P ≤ 0.05 between viruses.
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