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. 2013 Dec;7 Suppl 4(Suppl 4):21-6.
doi: 10.1111/irv.12194.

Swine influenza in Norway: a distinct lineage of influenza A(H1N1)pdm09 virus

Hilde Forberg  1 , Anna G Hauge, Britt Gjerset, Olav Hungnes, Anette Kilander
Affiliations

Swine influenza in Norway: a distinct lineage of influenza A(H1N1)pdm09 virus

Hilde Forberg et al. Influenza Other Respir Viruses. 2013 Dec.

Abstract

Background: Since the influenza A(H1N1)pdm09 virus was first introduced to the Norwegian pig population in September 2009, it has repeatedly been detected in pigs in Norway. No other subtypes of influenza virus are circulating in Norwegian pigs.

Objective: To follow the diversity of A(H1N1)pdm09 viruses circulating in pigs in Norway and to investigate the relationship between viruses circulating in Norwegian pigs and in humans.

Methods: Between January 2011 and January 2013, nasal swabs from 507 pigs were tested for A(H1N1)pdm09 virus by real-time RT-PCR. The hemagglutinin (HA) gene of virus-positive samples was sequenced and compared with publically available sequences from viruses circulating in humans at the time.

Results: Sequencing and phylogenetic analysis of the HA gene showed that the A(H1N1)pdm09 virus circulating in Norwegian pigs early in 2011 resembled the A(H1N1)pdm09 virus circulating in humans during this time. Viruses detected in pigs by the end of 2011 had acquired four characteristic amino acid substitutions (N31D, S84I S164F, and N473D) and formed a distinct phylogenetic group.

Conclusions: A(H1N1)pdm09 virus detected in Norwegian pigs by the end of 2011 formed a distinct genetic lineage. Also, our findings indicate that reverse-zoonotic transmission from humans to pigs of the A(H1N1)pdm09 virus is still important.

Keywords: Influenza A(H1N1)pdm09 virus; Norway; Public health; Swine.

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Figures

Figure 1
Figure 1
Phylogenetic reconstruction of the hemagglutinin gene (HA1 subunit) of influenza A(H1N1)pdm09 viruses from pigs in Norway, together with viruses from humans in Norway and elsewhere during the corresponding period. An alignment of the 981 nucleotides encoding the HA1 subunit was used. The evolutionary history was inferred using the neighbor‐joining method, from pairwise evolutionary distances computed using the Kimura 2‐parameter method. Bootstrap scores of 70 or higher (1000 replicates) are shown next to the branches. Norwegian isolates are in color. Viruses from pigs are in bold italics. International reference strains are in bold. The clade emerging in Norwegian pigs in late 2011 is indicated with a square.
See this image and copyright information in PMC

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