Co-infection of chickens with H9N2 and H7N9 avian influenza viruses leads to emergence of reassortant H9N9 virus with increased fitness for poultry and enhanced zoonotic potential

Abstract

SUMMARYAn H7N9 low pathogenicity avian influenza virus (LPAIV) emerged through genetic reassortment between H9N2 and other LPAIVs circulating in birds in China. This virus causes inapparent clinical disease in chickens, but zoonotic transmission results in severe and fatal disease in humans. We evaluated the consequences of reassortment between the H7N9 and the contemporary H9N2 viruses of G1 lineage that are enzootic in poultry across the Indian sub-continent and the Middle East. Co-infection of chickens with these viruses resulted in emergence of novel reassortant H9N9 viruses carrying genes derived from both H9N2 and H7N9 viruses. These reassortant H9N9 viruses showed significantly increased replication fitness, enhanced pathogenicity in chicken embryos and the potential to transmit via contact among ferrets. Our study highlights that the co-circulation of H7N9 and H9N2 viruses could represent a threat for the generation of novel reassortant viruses with greater virulence in poultry and an increased zoonotic potential. Graphical AbstractIn BriefH9N2 viruses have a high propensity to reassort with other avian influenza viruses. We found that co-infection of chickens with H9N2 and H7N9 led to the emergence of reassortant viruses including the H9N9 subtype. Some reassortant H9N9 viruses exhibited increased replication fitness, increased pathogenicity in the chicken embryo, greater avidity for human and avian cell receptors, lower pH fusion and contact-transmission to ferrets. This study demonstrated the ability of viruses that already exist in nature to exchange genetic material, highlighting the potential emergence of viruses from these subtypes with increased zoonotic potential. There are nine H9 influenza A subtypes carrying different neuraminidase (NA) genes, including H9N9 viruses, while they are not common they do exist in nature as wildtypes (CDC).HighlightsCo-infection of chickens with H7N9 and H9N2 led to emergence of reassortant H9N9 virusesReassortant H9N9 viruses had an increased replication rate in avian and human cellsReassortant H9N9 viruses had a lower pH fusion and significantly higher receptor binding to α 2,3 sialoglycansReassortant H9N9 replicated in ferrets at similar levels compared to H7N9 and transmitted via direct contactFerrets exposed to reassortant H9N9 by aerosol contact were also found to be seropositiveExperimental simulation of events that may occur naturally with circulating viruses has demonstrated the risk of emergence of viruses with increased zoonotic potential.