Neuraminidase Amino Acid Sequences of Influenza A/H3N2 and B Viruses Isolated from Influenza Patients in the 2014/15 Japanese Influenza Season.

Background: Neuraminidase (NA) is a surface protein essential for influenza virus replication. NA inhibitors are commonly used for the treatment of influenza patients in Japan. Several mutations that reduce the effect of NA inhibitors have been reported. We sequenced the whole NA segment of isolated virus from influenza patients and investigated the relation between the NA amino acid sequence and the 50％ inhibitory concentration (IC_50) of four NA inhibitors.

Materials and methods: Forty A/H3N2 and 19 B influenza virus isolated from patients in the 2014/15 influenza season were analyzed. The IC_50 was determined by a neuraminidase inhibition assay using a fluorescent substrate. Viral RNA was amplified by RT-PCR and the genome was sequenced using a next generation sequencer. The deduced amino acid sequences were analyzed.

Results: There was no AA change in the NA catalytic site of the A/H3N2 and B viruses isolated in the 2014-15 influenza season. There was no significant relation between the NA amino acids and the IC_50 of the four NA inhibitors for A/H3N2 or B viruses.

Conclusion: The catalytic site of NA was highly conserved for these A/H3N2 and B viruses. No emergence of NA amino acid mutations related to the sensitivity of the four currently used NA inhibitors was observed.