A reassortant H9N2 influenza virus containing 2009 pandemic H1N1 internal-protein genes acquired enhanced pig-to-pig transmission after serial passages in swine

Xavier Saelens,Kristien Van Reeth,Wenjun Ma,José Carlos Mancera Gracia,Juergen A Richt,Silvie Van Den Hoecke

doi:10.1038/s41598-017-01512-x

Xavier Saelens, Kristien Van Reeth + Show 4 more

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https://doi.org/10.1038/s41598-017-01512-x

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Abstract

Avian H9N2 and 2009 pandemic H1N1 (pH1N1) influenza viruses can infect pigs and humans, raising the concern that H9N2:pH1N1 reassortant viruses could emerge. Such reassortants demonstrated increased replication and transmissibility in pig, but were still inefficient when compared to pH1N1. Here, we evaluated if a reassortant virus containing the hemagglutinin and neuraminidase of A/quail/Hong Kong/G1/1997 (H9N2) in the A/California/04/2009 (pH1N1) backbone could become better adapted to pigs by serial passaging. The tropism of the original H9N2:pH1N1 (P0) virus was restricted to the nasal mucosa, with no virus detected in the trachea or lungs. Nevertheless, after seven passages the H9N2:pH1N1 (P7) virus replicated in the entire respiratory tract. We also compared the transmissibility of H9N2:pH1N1 (P0), H9N2:pH1N1 (P7) and pH1N1. While only 2/6 direct-contact pigs showed nasal virus excretion of H9N2:pH1N1 (P0) ≥five days, 4/6 direct-contact animals shed the H9N2:pH1N1 (P7). Interestingly, those four animals shed virus with titers similar to those of the pH1N1, which readily transmitted to all six contact animals. The broader tissue tropism and the increased post-transmission replication after seven passages were associated with the HA-D225G substitution. Our data demonstrate that the pH1N1 internal-protein genes together with the serial passages favour H9N2 virus adaptation to pigs.

Highlights

Avian H9N2 and 2009 pandemic H1N1 influenza viruses can infect pigs and humans, raising the concern that H9N2:pH1N1 reassortant viruses could emerge
The sporadic isolation of avian H9N2 influenza viruses from pigs and humans in China increases the possibility of co-infections with endemic swine or human influenza viruses, which could result in the generation of novel reassortant viruses with enhanced transmissibility in mammals
We have examined the replication and transmissibility after ten serial pig passages of a reassortant virus containing A/quail/Hong Kong/G1/1997 (H9N2) surface-protein genes and NP gene within the A/California/04/2009 background to evaluate if the pH1N1 backbone confers an advantage in H9N2 adaptation to pigs

Summary

Introduction

Avian H9N2 and 2009 pandemic H1N1 (pH1N1) influenza viruses can infect pigs and humans, raising the concern that H9N2:pH1N1 reassortant viruses could emerge. A significant proportion of poultry H9N2 field isolates contains a leucine instead of glutamine residue at position 226 in the hemagglutinin (HA) receptor-binding site (RBS) (HA-Q226L, H3 numbering used throughout) This mutation has been shown to enhance HA binding to terminal α2,6-linked sialic acids (Siaα2,6Gal) and to improve the replication of H9N2 viruses in human airway epithelial cells in vitro, supporting concerns about their pandemic potential[10,11,12]. The sporadic isolation of avian H9N2 influenza viruses from pigs and humans in China increases the possibility of co-infections with endemic swine or human influenza viruses, which could result in the generation of novel reassortant viruses with enhanced transmissibility in mammals

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