Epidemiological and genetic characteristics of H5 subtype avian influenza virus in Guangzhou, 2014-2019

Abstract

Objective: To analyze the characteristics of spread and genetic evolution of H5 subtype avian influenza virus in Guangzhou from 2014 to 2019. Methods: H5 subtype virus was detected by fluorescence quantitative RT-PCR from the environmental samples in Guangzhou poultry markets. The genes of HA and NA of 48 isolates randomly selected were sequenced, including 46 isolates from environmental samples and 2 isolates from cases. The characteristics of molecular variation and genetic evolution were analyzed by using bioinformatics software. Results: A total of 1 094 strains of H5 subtype avian influenza virus were isolated from 52 284 samples (2.09%). All the strains belonged to Clade 2.3.4.4.C. NA gene belonged to H6N6 of Eurasian lineage. The cleavage sites of all the strains showed the characteristics of highly pathogenicity. Receptor binding sites were avian-derived receptors. However, mutations of S123P, S133A and T156A occurred, which implied that these strains could tend to bind to human receptors. There was an additional glycosylation site at 140 in strains isolated after 2017. The variation of antigen loci mainly occurred in B and E regions. Conclusions: H5 subtype avian influenza virus spread in Guangzhou from 2014 to 2019 with annual increased proportion of positive rate, and the sequencing results indicated that it belonged to Clade 2.3.4.4.C of H5N6 highly pathogenic virus, and genetic evolution and mutation continued, especially the common mutations which could enhance the binding capacity to human receptors. It is necessary to strengthen the surveillance.