Analysis on hemagglutinin gene characterizes of avian influenza A (H7N9) virus infection in Suzhou city during 2016—2017

Abstract

Objective To analyze epidemiological and genetic characteristics of the fifth avian influenza A (H7N9) wave in Suzhou, and to provide scientific basis for prevention and control of H7N9 virus infection. Methods Respectively, influenza A/B, H1N1 (pdm09), H3, H5N1, and H7N9 real-time PCR kits were used to detected pharyngeal swab samples which were collected from severe acute respiratory syndrome infection (SARI) cases in Suzhou. The H7N9-positive samples were further examined for virus isolation and gene sequencing. Results The H7N9 virus was mainly prevalent in winter in Suzhou City. In the fifth H7N9 virus epidemic, the overall fatality rate of human infection with H7N9 virus in Suzhou city was 40% (22/55). Additionally, most were older people (median age was 58 years) and more than 80% of H7N9 patients had live poultry exposure history. The nucleic acid homology of HA gene was 98.7-100%. There were no mutations in the key sites of the HA gene sequence. Conclusions The H7N9 virus can not be effectively spread in the crowd currently, with no significant changes in receptor binding sites (RBS). In addition, exposure to live poultry or contaminated environment is still the main source of human infection with H7N9. At present, the viruses circulating in Suzhou city are low pathogenic to poultry. Key words: Avian influenza; Hamagglutinin gene; Severe acute respiratory syndrome infection (SARI); Real-time PCR; Influenza A (H7N9)