Objective To understand the genome and genetic evolution characteristics of influenza B virus (FluB) in Suzhou city from July 2021 to January 2022.
Methods Real-time fluorescence reverse transcription polymerase chain reaction (Real-Time RT-PCR) was used for the typing of influenza virus (Flu). The detected FluB strains were sequenced by Miseq high-throughput sequencing platform through whole genome capture and library construction. The FluB hemagglutinin (HA), neuraminidase (NA) and matrix protein (MP) gene phylogenetic trees were constructed by Neighbor-Joining method (NJ) with MEGA X software. The Potential N-glycosylation sites of HA and NA proteins were predicted by NetNGlyc 1.0 server software.
Results FluB was detected in 280 of the 1 500 throat swab samples, and the FluB genome sequence was completed in 53 strains. The nucleic acid identity of 8 gene fragments (PB1, PB2, PA, HA, NP, NA, MP, NS) in the FluB strains was 99.3%-100%, 98.1%-100%, 98.8%-100%, 98.0%-100%, 99.2%-100%, 98.4%-100%, 98.2%-100% and 99.0%-100%, respectively. Except for the 4 samples in July 2021, which belonged to the V1A.3 clade of FluB, the rest of the samples belonged to the V1A.3a.2 clade. Every amino acid sequence of HA protein of Flu B collected after October 2021 showed 9-11 substitutions compared with the reference strain (B/Washington/02/2019), which sharing 9 mutation sites (H122Q, A127T, R133G, P144L, N150K, G184E, N197D, K203R and R279K). No drug-resistant mutations associated with NA inhibitors such as oseltamivir were found. Respectively, 11 and 4 potential glycosylation sites were identified in HA and NA proteins of the FluB strains.
Conclusions From July 2021 to January 2022, V1A.3a2 was the dominant FluB strains in Suzhou city, and the amino acid sequences of HA and NA proteins showed multiple site mutations.