Evolutionary characteristics of A/Hangzhou/1/2013 and source of avian influenza virus H7N9 subtype in China.

A patient with an influenza-like illness was first admitted to a hospital in Shanghai on 19 February 2013, and another similar case appeared 8 days later. Both patients died after approximately 2 weeks. The National Health and Family Planning Commission of China officially affirmed the pathogen being a new avian influenza virus (AIV) H7N9 subtype. Up to 20 April, 87 cases in humans were confirmed, 17 of whom died [1]. This study investigated the source of the virus and evolution. We first conducted a homology analysis using MegAlign module of Lasergene7.0 software on an AIV isolate A/ Hangzhou/1/2013 (GenBank accession number KC853766) and found that its hemagglutinin (HA) gene was highly homologous to a strain A/duck/Zhejiang/12/ 2011 (H7N3) (accession number JQ906576) isolated in Hangzhou city (95.8% and 97.9% for nucleotide and derived amino acid sequences), which is likely the provider of HA gene of the H7N9 subtype. The neuraminidase (NA) gene of the AIV isolate A/Hangzhou/1/2013 (GenBank accession number KC853765) was highly homologous with the isolate A/mallard/ Czech Republic/13 438–29K/2010 (H11N9)