Characterisation of Influenza H1N1 viruses resistant to Oseltamivir

Session VII – Lackenby, Angie – Young Investigator Applicant

Title of Contribution: Characterisation of Influenza H1N1 viruses resistant to Oseltamivir

Author(s): Angie Lackenby1, Catherine Thompson1, Patrick Collins2, Monica Galliano1, Joanna Ellis1, Vicky Gregory2, Rod Daniels2, Alan Hay2 and Maria Zambon1

Affiliation(s): 1Respiratory Virus Unit, Centre for Infection, Health Protection Agency, London, UK; 2MRC National Institute for Medical Research, Department of Virology, London UK

Abstract:
Influenza A H1N1 viruses resistant to the neuraminidase inhibitor oseltamivir emerged in the last quarter of 2007 and early 2008. These viruses were antigenically similar to A/Brisbane/59/2007, and an H275Y mutation in the neuraminidase protein was responsible for the antiviral resistant phenotype. Isolation of this variant did not correlate with drug use. H1N1 viruses with this mutation have occurred at low frequency (<1%), but in contrast to previous observations, these resistant viruses were able to spread globally in 2008.
To investigate the properties of H1N1 viruses, we undertook detailed phylogenetic analyses of the HA and NA genes as well as comparisons of whole genome sequences of resistant and sensitive viruses circulating since 1978. NA enzyme and virus growth kinetic analyses on a panel of temporally and geographically matched pairs of oseltamivir sensitive and resistant viruses which arose with and without drug treatment were also carried out to identify characteristics of resistance from different clinical circumstances. We also performed competitive co-infections of paired viruses to identify any growth kinetics differences between sensitive and resistant viruses from different clades.
Examination of whole genome sequences indicates that emergence and spread of H275Y resistance is not due to a single point source. Growth kinetics studies showed that sensitive and resistant viruses were equivalent in their replicative capacity and enzyme kinetics analyses showed a correlation of higher affinity for substrate with particular mutations in the neuraminidase gene in clade 2B and 2C viruses.
Alterations in substrate affinity of the NA enzyme and mutations in the PB2 and PB1F2 may contribute to the ability to tolerate the usually debilitating H275Y mutation, thus increasing the fitness of virus strains carrying this mutation.