Oseltamivir- and Zanamivir-Resistance Related Mutations in Influenza A Viruses Isolated from Wild Mallards in Sweden Studied by a Colorimetric Neuraminidase Inhibition Assay
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Resistance to neuraminidase inhibitors (NAIs) is a growing problem in the battle against influenza A viruses. However, little is known about the resistance of viruses isolated from dabbling ducks, the natural reservoir of the influenza virus. To date, no low-pathogenic avian influenza (LPAI) virus functionally resistant to NAIs has been detected. The aim of this study was to investigate mallard isolates of influenza A virus previously identified to carry oseltamivir carboxylate (OC)- or zanamivir (ZA)-related resistance mutations. In this work, 21 viruses belonging to the N1, N3, N6 and N9 subtypes were analyzed using a colorimetric NA inhibition assay. The R118K mutation was the most frequently observed; it was seen in all subtypes except for N6. IC50 values confirmed the differences in sensitivity to OC or ZA previously observed in the N1 and N2 groups of NAs. Furthermore, both negative controls (NCs) in the N6 and one NC in the N9 subtype were less sensitive to ZA than were genotypically related mutants of the respective subtypes. The presence of OC- and ZA-related mutations in the NA of viruses isolated from wild birds did not result in a NAI-resistant phenotype in this study. The R118K and R152K mutations seemed to somewhat increase the sensitivity to both NAIs compared to WT viruses which supports the thought that the mutations were a result of natural NA variation and not induced by NAI residuals in the environment. Although not resulting in a NAI resistant phenotype, the finding of the mutations D151N and I222V shows that mutations with the potential to enhance NAI resistance exist in the pool of LPAI viruses which stresses the need for surveillance of NAI resistance in wild birds.
Microbiology in the medical area Microbiology
IdentifiersURN: urn:nbn:se:uu:diva-160966OAI: oai:DiVA.org:uu-160966DiVA: diva2:453742