Swine influenza in Norway: a distinct lineage of influenza A(H1N1)pdm09 virus.
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.
Section of Virology, Norwegian Veterinary Institute, Oslo, Norway.
Hilde
H
Forberg
Anna G
AG
Hauge
Britt
B
Gjerset
Olav
O
Hungnes
Anette
A
Kilander
D000595:Amino Acid Sequence; D000818:Animals; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D008969:Molecular Sequence Data; D009664:Norway / Q000453:epidemiology; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D010802:Phylogeny; D016415:Sequence Alignment; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000821:virology*
D019267:Hemagglutinin Glycoproteins, Influenza Virus
Influenza A(H1N1)pdm09 virus; Norway; Public health; Swine