Characterisation of an influenza B variant selected with the neuraminidase inhibitor zanamivir

Abstract

In order to study the generation of influenza viruses resistant to neuraminidase (NA) inhibitors, a recent influenza type B virus was passaged in vitro in the presence of increasing concentrations of zanamivir (0.1–1000 μM). A total of nine passages were carried out and, following the fifth passage at 10 μM, a mutation in the neuraminidase gene at Glu 119 Asp (N2 numbering) which is part of the enzyme active site was observed. Following another three passages in 100 μM of zanamivir, a further mutation in the HA1 domain of the haemagglutinin (HA) (Gln 218 Lys) (H3 numbering) was found. When compared with the wild-type virus, the passage levels containing the NA mutation exhibited a 32,000-fold reduction in sensitivity to zanamivir and a 105-fold reduction to oseltamivir carboxylate using a fluorescence-based neuraminidase inhibition assay. As a result of the mutation in the HA1 region of the haemagglutinin, a minor reduction in receptor binding strength in vitro was observed compared with the wild-type.