Molecular epidemiologic characteristics of hemagglutinin from five waves of avian influenza A (H7N9) virus infection, from 2013 to 2017, in Zhejiang Province, China

Yi Sun,Xiuyu Lou,Yanjun Zhang,Xinying Wang,Biaofeng Zhou,Yin Chen,Haiyan Mao

doi:10.1007/s00705-021-05233-5

Abstract

There have been five waves of influenza A (H7N9) epidemics in Zhejiang Province between 2013 and 2017. Although the epidemiological characteristics of the five waves have been reported, the molecular genetics aspects, including the phylogeny, evolution, and mutation of hemagglutinin (HA), have not been systematically investigated. A total of 154 H7N9 samples from Zhejiang Province were collected between 2013 and 2017 and sequenced using an Ion Torrent Personal Genome Machine. The starting dates of the waves were 16 March 2013, 1 July 2013, 1 July 2014, 1 July 2015, and 1 July 2016. Single-nucleotide polymorphisms (SNPs) and amino acid mutations were counted after the HA sequences were aligned. The evolution of H7N9 matched the temporal order of the five waves, among which wave 3 played an important role. The 55 SNPs and 14 amino acid mutations with high frequency identified among the five waves revealed the dynamic occurrence of mutation in the process of viral dissemination. Wave 3 contributed greatly to the subsequent epidemic of waves 4 and 5 of H7N9. Compared with wave 1, wave 5 was characterized by more mutations, including A143V and R148K, two mutations that have been reported to weaken the immune response. In addition, some amino acid mutations were observed in wave 5 that led to more lineages. It is necessary to strengthen the surveillance of subsequent H7N9 influenza outbreaks.

Highlights

The first case of avian influenza A/H7N9 virus infection in humans was reported in 2013 in eastern China [4]
Single-nucleotide polymorphisms (SNPs) and amino acid mutations were counted after the HA sequences were aligned
From March 2013 to June 2017, there were a total of 320 H7N9 human infections, including 116 fatal cases, reported in Zhejiang Province, China

Summary

Introduction

The first case of avian influenza A/H7N9 virus infection in humans was reported in 2013 in eastern China [4]. The first wave emerged in the Yangtze River Delta, and subsequently, the spatial range of H7N9 human cases increased, along with lineage alterations during epidemic wave 2 [17]. Lineages of wave 5 from the Yangtze River Delta and Pearl River Delta have been different [6]. Zhejiang Province is considered one of the likely areas for the emergence of H7N9 in the Yangtze River Delta, the virus was first recognized in Shanghai (A/Shanghai/1) [4, 17]. We reported the epidemiological characteristics of the five epidemic waves of H7N9 infection in Zhejiang Province, concluding that the epidemic crossregional expansion continued and mostly occurred in rural areas [16]. We investigated the phylogenetic pattern and dynamic evolution of H7N9 in Zhejiang since it emerged in 2013, which may contribute to the prevention and control of H7N9 in the future

Materials and methods

Results

Discussion