Estimating the fitness advantage conferred by permissive neuraminidase mutations in recent oseltamivir-resistant A(H1N1)pdm09 influenza viruses.

Jeff Butler,Lucia Reh,Sophie Vitesnik,Lumin Xue,Chantal Baas,James M Mccaw,Sebastian Maurer-Stroh,Sook-Kwan Leang,Stephen Petrie,Teagan Guarnaccia,Anne Kelso,Aeron C Hurt,Kathryn A Hooper,Jodie Mcvernon,Raphael Lee,Ian G Barr,Jesse D Bloom,Daniel R Perez

doi:10.1371/journal.ppat.1004065

Abstract

Oseltamivir is relied upon worldwide as the drug of choice for the treatment of human influenza infection. Surveillance for oseltamivir resistance is routinely performed to ensure the ongoing efficacy of oseltamivir against circulating viruses. Since the emergence of the pandemic 2009 A(H1N1) influenza virus (A(H1N1)pdm09), the proportion of A(H1N1)pdm09 viruses that are oseltamivir resistant (OR) has generally been low. However, a cluster of OR A(H1N1)pdm09 viruses, encoding the neuraminidase (NA) H275Y oseltamivir resistance mutation, was detected in Australia in 2011 amongst community patients that had not been treated with oseltamivir. Here we combine a competitive mixtures ferret model of influenza infection with a mathematical model to assess the fitness, both within and between hosts, of recent OR A(H1N1)pdm09 viruses. In conjunction with data from in vitro analyses of NA expression and activity we demonstrate that contemporary A(H1N1)pdm09 viruses are now more capable of acquiring H275Y without compromising their fitness, than earlier A(H1N1)pdm09 viruses circulating in 2009. Furthermore, using reverse engineered viruses we demonstrate that a pair of permissive secondary NA mutations, V241I and N369K, confers robust fitness on recent H275Y A(H1N1)pdm09 viruses, which correlated with enhanced surface expression and enzymatic activity of the A(H1N1)pdm09 NA protein. These permissive mutations first emerged in 2010 and are now present in almost all circulating A(H1N1)pdm09 viruses. Our findings suggest that recent A(H1N1)pdm09 viruses are now more permissive to the acquisition of H275Y than earlier A(H1N1)pdm09 viruses, increasing the risk that OR A(H1N1)pdm09 will emerge and spread worldwide.

Highlights

The influenza NA inhibitor antiviral drug oseltamivir is a key element of public health defences against influenza, and was used during the early stages of the A(H1N1)pdm09 influenza pandemic to lessen the burden of disease in infected patients [1,2]
Using reverse engineered viruses we demonstrate that a pair of permissive secondary NA mutations, V241I and N369K, confers robust fitness on recent H275Y A(H1N1)pdm09 viruses, which correlated with enhanced surface expression and enzymatic activity of the A(H1N1)pdm09 NA protein
We demonstrate that two novel amino acid changes present in virtually all recent A(H1N1)pdm09 viruses (NA V241I and N369K) enable the acquisition of the NA H275Y oseltamivir resistance mutation without compromising viral fitness

Summary

Introduction

The influenza NA inhibitor antiviral drug oseltamivir is a key element of public health defences against influenza, and was used during the early stages of the A(H1N1)pdm influenza pandemic to lessen the burden of disease in infected patients [1,2]. The most common oseltamivir resistance (OR) mutation detected in A/H1N1 viruses is the NA H275Y mutation. Prior to 2007, the incidence of OR influenza viruses was generally low (,1%) [3,4,5,6,7]. In vitro and in vivo virological studies demonstrated that OR seasonal A(H1N1) viruses had attenuated viral replication kinetics in cell culture, mice and ferrets [8,9,10], and were considered to pose only a minimal threat to public health [8]. In 2008, OR (H275Y) seasonal A(H1N1) viruses emerged and spread globally within 12 months, in the absence

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