Airborne Transmission of Avian Origin H9N2 Influenza A Viruses in Mammals.

C Joaquín Cáceres,Daniela S Rajao,Daniel R Perez

doi:10.3390/v13101919

Abstract

Influenza A viruses (IAV) are widespread viruses affecting avian and mammalian species worldwide. IAVs from avian species can be transmitted to mammals including humans and, thus, they are of inherent pandemic concern. Most of the efforts to understand the pathogenicity and transmission of avian origin IAVs have been focused on H5 and H7 subtypes due to their highly pathogenic phenotype in poultry. However, IAV of the H9 subtype, which circulate endemically in poultry flocks in some regions of the world, have also been associated with cases of zoonotic infections. In this review, we discuss the mammalian transmission of H9N2 and the molecular factors that are thought relevant for this spillover, focusing on the HA segment. Additionally, we discuss factors that have been associated with the ability of these viruses to transmit through the respiratory route in mammalian species. The summarized information shows that minimal amino acid changes in the HA and/or the combination of H9N2 surface genes with internal genes of human influenza viruses are enough for the generation of H9N2 viruses with the ability to transmit via aerosol.

Highlights

Influenza A viruses (IAV) are members of the family Orthomyxoviridae with a segmented RNA genome of negative polarity
IAVs of avian origin are classified into high pathogenicity avian influenza viruses (HPAIVs) and low pathogenicity avian influenza viruses (LPAIVs) based on the pathotype in chickens and/or the presence of a polybasic amino acid cleavage site composed of Arginine (R) or Lysine (K) [10]
Recent H9N2 isolates from Asia and Middle East have increasingly shown the presence of a tri-basic HA cleavage site, which was associated with increased pathogenicity and transmission in chickens in comparison with viruses with mono-basic cleavage sites [16]

Summary

Introduction

Influenza A viruses (IAV) are members of the family Orthomyxoviridae with a segmented RNA genome of negative polarity. Recent H9N2 isolates from Asia and Middle East have increasingly shown the presence of a tri-basic HA cleavage site, which was associated with increased pathogenicity and transmission in chickens in comparison with viruses with mono-basic cleavage sites [16]. These viruses with the tri-basic cleavage site did not demonstrate a HPAI phenotype but rather an intermediate step towards a gain in pathogenicity, and were still considered LPAIV. Viruses of the H5 or H7 subtypes have been associated with the HPAI pathotype

H9N2 Avian Influenza Viruses

Molecular Mechanisms Associated with Interspecies Transmission of IAVs

Directly inoculated 5

Natural Infection of H9N2 IAV in Mammals

Findings

Directly inoculated