Ongoing genetic evolution of H9N2 avian influenza viruses in Iranian industrial poultry farms

Abstract

Despite the use of wide-scale vaccination programmes against the H9N2 virus, enzootic outbreaks of H9N2 avian influenza (AI) have often occurred and caused serious nationwide economic losses, particularly in broiler chickens. In this study, the haemagglutinin (HA) and neuraminidase (NA) genes of nine recent H9N2s and a common vaccine strain were fully sequenced and compared with other representative Iranian viruses. Phylogenetic analysis revealed that all Iranian viruses were grouped into the G1 sub-lineage with different clusters in which recent isolates (2014–2017) formed a distinct cluster compared to the vaccine group (1998–2004). All Iranian H9N2s exhibited low pathogenicity AI connecting peptide feature with an R/KSSR motif. Amino acid 226, located in the 220 loop of the receptor binding site, was leucine among the recent Iranian viruses, a characteristic of human influenza viruses. With an overall gradual increase in the genetic diversity of H9N2s, Bayesian skyline plots of Iranian HA and NA genes depicted a fluctuation and a relative stable situation, respectively. It is recommended to apply constant surveillance to assess any increase in viral human adaptation and evolutionary changes in circulating field H9N2s. Moreover, antigenic characterisation of the prevailing H9N2 viruses seems to be necessary for evaluating the possible antigenic drift from the vaccine strain.

Wild bird trade at live poultry markets potentiates risks of avian influenza virus introduction in Iran

“…For several of these clusters an immediate ancestor can be found in one of the neighboring countries of Iran, Iraq, or Pakistan. This suggests incursions of G1-like H9N2 to Iran by transboundary poultry trade rather than by wild birds [ 28 , 29 ]. Unlike the Y439 wild bird H9N2 viruses examined here, the Iranian G1-like viruses harbor mutations (e.g., HA Q226L) that increase their zoonotic potential [ 28–30 ].…”

“…This suggests incursions of G1-like H9N2 to Iran by transboundary poultry trade rather than by wild birds [ 28 , 29 ]. Unlike the Y439 wild bird H9N2 viruses examined here, the Iranian G1-like viruses harbor mutations (e.g., HA Q226L) that increase their zoonotic potential [ 28–30 ]. In addition, sets of internal genes of H9N2 viruses have been widely implicated in reassortment events with HPAIV of the gs/GD lineage and with other subtypes, including H10 [ 10–12 ].…”