| Avian influenza (AI) is an infectious disease caused by influenza A virus within the orthomyxoviridae family. It can be separated into three types, namely low pathogenic AI, high pathogenic AI and non pathogenic AI. H9N2is the main subtype of low pathogenic AI in China. The widespread and outbreaks of AI impose big losses in poultry breeding industry every year. The recent research showed that the avian influenza viruses are gradually breaking the species barrier between poultry and mammals, especially some special mutations in H9N2virus impose the risk of AIV transmitting to human and mammals. Vaccination was the most universal and useful method used in China to prevent and control the disease, while the side effect was that the mutation and recombination of AIVs appeared even more frequent. So it is important to monitor the prevalence state of AIVs and analysis the genetic evolution of the latest prevalent strains for disease control. In this study, we carried out the genetic evolution analysis of44H9N2strains isolated in Eatern China during2010to2012. Then we charaterized one candidate vaccine strain and valued its preventive effect.In order to make clear the prevalence state of all subtypes of AIVs, we chose one big Live Bird Market in eastern China to conduct the epidemiology survey. We collected about200poultry cloaca swabs in the market every month from July2011to Jun2012to isolate AIVs. As a result, we totally collected2326swabs, and374were positive ones, the positive rate was16.08%. The main subtypes of the prevalent strains were H3, H4, H6and H11, and mainly isolated from aquatic bird. The isolation rate was higher in winter and autumn than that in summer and spring.We sequenced the whole-genome of44H9N2strains isolated during2010to2012and drew phylogenetic trees to analysis the genetic evolution of the H9N2virus in vogue recent years. The results showed that the recent H9N2AIVs formed a new genotype different from SH/F/98, designated as V genotype. The external gene HA belonged to HK/Y280/97-like sublineage different from Ck/SH/F/98-like, because its nucleotide homology and deduced amino acid homology were just88.8%-92.4%and90.3%-93.8%respectively compared with SH/F/98, while the homology were higher when compared with HK/Y280/97. There were many mutations in antigen site, and the receptor binding site226was L with no exception among all79isolates. The internal genes were mainly Ck/SH/F/98-like, except that M gene was HK/G1/97-like.One of the goals of epidemiology survey was to select candidate vaccine strain. We finally chose the isolate WJ57as the candidate vaccine strain based on the antigenic analysis and biological characteristics of all H9N2viruses in this research. The strain WJ57was isolated in chicken in Jiangsu province, China,2012. The HA titer of which was10-11log2, and the EID50was9.17log10/0.1ml, these means good multiplication capacity. In addition, it was thermostable and highly homologous to other H9N2isolates. The cross-hemagglutination inhibition test showed that the HI titer of chicken serum could reach91og221days post vaccination with inactivated vaccine made by WJ57, it was at least2titers higher than that of F/98. The protection rate of WJ57was93.3%, higher than80%of SH/F/98. All these revealed that the WJ57was a good candidate vaccine strain. |
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