Characterization of drug-resistant influenza A(H7N9) variants isolated from an oseltamivir-treated patient in Taiwan

J Infect Dis. 2015 Jan 15;211(2):249-57. doi: 10.1093/infdis/jiu447. Epub 2014 Aug 14.


Background: Patients contracting influenza A(H7N9) infection often developed severe disease causing respiratory failure. Neuraminidase (NA) inhibitors (NAIs) are the primary option for treatment, but information on drug-resistance markers for influenza A(H7N9) is limited.

Methods: Four NA variants of A/Taiwan/1/2013(H7N9) virus containing a single substitution (NA-E119V, NA-I222K, NA-I222R, or NA-R292K) recovered from an oseltamivir-treated patient were tested for NAI susceptibility in vitro; their replicative fitness was evaluated in cell culture, mice, and ferrets.

Results: NA-R292K led to highly reduced inhibition by oseltamivir and peramivir, while NA-E119V, NA-I222K, and NA-I222R caused reduced inhibition by oseltamivir. Mice infected with any virus showed severe clinical signs with high mortality rates. NA-I222K virus was the most virulent in mice, whereas virus lacking NA change (NA-WT) and NA-R292K virus seemed the least virulent. Sequence analysis suggests that PB2-S714N increased virulence of NA-I222K virus in mice; NS1-K126R, alone or in combination with PB2-V227M, produced contrasting effects in NA-WT and NA-R292K viruses. In ferrets, all viruses replicated to high titers in the upper respiratory tract but produced only mild illness. NA-R292K virus, showed reduced replicative fitness in this animal model.

Conclusions: Our data highlight challenges in assessment of the replicative fitness of H7N9 NA variants that emerged in NAI-treated patients.

Keywords: E119V; H7N9; I222K; I222R; R292K; ferrets; influenza virus; mice; oseltamivir; peramivir.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antiviral Agents / therapeutic use*
  • Disease Models, Animal
  • Drug Resistance, Viral*
  • Ferrets
  • Humans
  • Influenza A Virus, H7N9 Subtype / drug effects*
  • Influenza A Virus, H7N9 Subtype / enzymology
  • Influenza A Virus, H7N9 Subtype / genetics
  • Influenza A Virus, H7N9 Subtype / isolation & purification
  • Influenza, Human / drug therapy*
  • Influenza, Human / virology*
  • Mice, Inbred BALB C
  • Microbial Sensitivity Tests
  • Mutant Proteins / genetics
  • Mutation, Missense
  • Neuraminidase / genetics
  • Orthomyxoviridae Infections / pathology
  • Orthomyxoviridae Infections / virology
  • Oseltamivir / therapeutic use*
  • Viral Proteins / genetics
  • Virus Cultivation
  • Virus Replication


  • Antiviral Agents
  • Mutant Proteins
  • Viral Proteins
  • Oseltamivir
  • NA protein, influenza A virus
  • Neuraminidase