Compatibility of H9N2 avian influenza surface genes and 2009 pandemic H1N1 internal genes for transmission in the ferret model

Abstract

In 2009, a novel H1N1 influenza (pH1N1) virus caused the first influenza pandemic in 40 y. The virus was identified as a triple reassortant between avian, swine, and human influenza viruses, highlighting the importance of reassortment in the generation of viruses with pandemic potential. Previously, we showed that a reassortant virus composed of wild-type avian H9N2 surface genes in a seasonal human H3N2 backbone could gain efficient respiratory droplet transmission in the ferret model. Here we determine the ability of the H9N2 surface genes in the context of the internal genes of a pH1N1 virus to efficiently transmit via respiratory droplets in ferrets. We generated reassorted viruses carrying the HA gene alone or in combination with the NA gene of a prototypical H9N2 virus in the background of a pH1N1 virus. Four reassortant viruses were generated, with three of them showing efficient respiratory droplet transmission. Differences in replication efficiency were observed for these viruses; however, the results clearly indicate that H9N2 avian influenza viruses and pH1N1 viruses, both of which have occasionally infected pigs, have the potential to reassort and generate novel viruses with respiratory transmission potential in mammals.

Replication and transmission of mammalian-adapted H9 subtype influenza virus in pigs and quail

“…To test the effect of mammalian-adapted (ferret-adapted) mutations of the H9 HA (Kimble et al, 2011;Sorrell et al, 2009) for replication and transmission in pigs and quail, five viruses were prepared (Table 1). Viruses containing the ferret-adapted H9 HA gene segment from the A/ferret/ Maryland/P10_UMD/2008 (H9N2) virus (2P10 : 6WF10, 2P10 : 6pdm and 1P10 : 7pdm) were rescued in the context of the avian-origin A/guinea fowl/Hong Kong/WF10/ 1999 (H9N2) (WF10, G1 lineage) or the pandemic-origin A/Netherlands/602/2009 (H1N1) (H1N1pdm).…”

“…We reported previously that three amino acid changes in the surface genes of an avian H9N2 virus conferred efficient airborne transmission of a reassortant H9N2 : H3N2 virus in the ferret model (Sorrell et al, 2009). We further showed that, on the H1N1pdm backbone, the two changes in the HA alone were sufficient for airborne transmission in ferrets without further adaptation (Kimble et al, 2011). In this study, we sought to determine whether the ferret-adaptive mutations would restrict the host range of these viruses in other natural hosts of influenza.…”

“…We further showed that following mammalian adaptation of the 2WF10 : 6M98 virus in ferrets, a ferret-adapted virus emerged, 2P10 : 6M98, in which only three amino acid changes in the surface genes (T189A in HA1, G192R in HA2 and I28V in the NA) were sufficient for airborne transmission to indirect-contact ferrets (Sorrell et al, 2009). Transferring the HA gene segment of the 2P10 : 6M98 virus (with or without the NA gene segment) into the H1N1pdm backbone (1P10 : 7pdm or 2P10 : 6pdm) also allowed efficient airborne transmission in ferrets (Kimble et al, 2011(Kimble et al, , 2014.…”

“…In this regard, it is important to note that the ferret is widely used as an animal model to study airborne transmission of influenza viruses; adaptive changes that lead to such a phenotype have been identified in the H9, H7 and H5 subtypes (Herfst et al, 2012;Imai et al, 2013;Kimble et al, 2011;Ku et al, 2014;Li et al, 2014;Sorrell et al, 2009;Sutton et al, 2014;Wan et al, 2008). However, further studies are lacking to demonstrate whether the ferret-adaptive mutations increase or restrict the host range of the virus.…”

“…Homosubtypic and heterosubtypic H9N2 reassortants have been isolated from both birds and swine in nature (Abolnik et al, 2007;Cong et al, 2007;Wang et al, 2012;Wu et al, 2015;Yu et al, 2008Yu et al, , 2011. Under experimental conditions, H9N2 viruses also demonstrate compatibility for reassortment, especially with regard to human seasonal H3N2 and H1N1pdm viruses, with many reassortants showing increased infectivity, transmissibility and pathogenicity in mice and ferrets (Kimble et al, 2011(Kimble et al, , 2014Qiao et al, 2012;Sorrell et al, 2009;Sun et al, 2011;Wan et al, 2008) We previously reported that a reassortant virus having surface genes from an avian H9N2 virus (A/guinea fowl/ Hong Kong/WF10/1999) and internal genes from a human H3N2 virus (A/Memphis/14/1998) -herein referred to as 2WF10 : 6M98 -were transmitted only to direct-contact (DC) ferrets (Wan et al, 2008). We further showed that following mammalian adaptation of the 2WF10 : 6M98 virus in ferrets, a ferret-adapted virus emerged, 2P10 : 6M98, in which only three amino acid changes in the surface genes (T189A in HA1, G192R in HA2 and I28V in the NA) were sufficient for airborne transmission to indirect-contact ferrets (Sorrell et al, 2009).…”