深圳市2005-2007年H3N2亚型流行性感冒病毒流行病学和分子变异特征

目的 探讨深圳市2005-2007年季节性流行性感冒(简称流感)流行病学特征和甲3亚型流感病毒可能的分子变异.方法 对深圳市2005-2007年流感监测网络(由9所医院、6个区和市疾病预防控制中心共16个主要机构组成)的运行质量进行控制,按周统计分析主要监测医院流感样病例占就诊者的百分比(ILI百分比),并采集流感样病例鼻咽拭子进行流感病毒分离鉴定,对分离到的毒株提取病毒RNA,用反转录聚合酶链式反应(RT-PCR)扩增血凝素基因重链区(HAI区)基因片段,产物纯化后测序并进行核苷酸相似性、基因进化树和氨基酸变异分析.结果 深圳市2005-2007年流感活动水平在各年间有所波动,呈现夏季高峰,2006和2007年5-7月为流行高峰期.2005-2007年流感病毒的分离率分别为4.78%(114/2385)、5.77%(212/3674)和12.12%(343/2831),分离毒株数多少与ILI百分比的季节波动相关,按周分离率与ILI百分比的变化趋势基本一致.2005和2006年甲3亚型所占比例分别为25.46%(28/114)和2.83%(6/212),而2007年成为优势毒株,占62.68%(215/343).甲3亚型病毒HA1区序列进化树分析发现,虽然进化树的主干基本按照毒株分离的时间先后发展,与不同年度WHO推荐的疫苗株先后一致,但2005-2007年的主要流感毒株共分为5个分支,2005-2006年毒株在第Ⅰ～Ⅲ分支,2007年4-6月和5-12月形成2个分支,与同期WHO推荐的疫苗株不在一个进化分支,深圳甲3亚型流感病毒的变化较早,出现疫苗株滞后现象.所有毒株未见HA1区序列缺失和插入,受体结合位点和二硫键位点氨基酸也显保守,一些位点出现了不同属性氨基酸的置换,并导致个别潜在的糖基化位点的丢失或增加,但尚不能判定为新变种.结论 深圳市可能属于我国流感病毒变异较早的地区之一,甲3亚型流感病毒在人群中呈活跃状态;常规季节性流感监测与病毒分子变异分析结合,能为毒株的演变及其流行病学意义提供及时、重要的信息.

Epidemiological and molecular characterization of seasonal influenza A/H3N2 viruses circulating in Shenzhen,2005-2007

Objective To determine the epideroiological characteristics of seasonal influenza in Shenzhen from 2005 to 2007 and the molecular variation of HA1 domain of influenza H3N2 viruses. Methods The consultation rate for influenza-like illness (ILI) were calculated weekly for indicating the influenza activities(the Shenzhen Influenza Surveillance System mainly consisted of 16 institutions with 9 hospitals,6 districts and one municipal centers of disease control and prevention). Pharyngeal swabs from the cases of ILI, which were collected during 2005 to 2007 from the city-wide and quality-controlled surveillance network, were used to propagate the viruses. The HA1 region of the influenza A/H3N2 viruses were detected by RT-PCR and sequenced subsequently. The analyses of pairwise amino acid variations, genetic clustering and phylogeneties was performed. Results The activity levels of influenza showed certain changes during each year from 2005 to 2007,and there were summer peaks from May to July in 2006 and 2007. The positive rates of influenza virus were 4.78% (114/2385),5.77% (212/3674) and 12.12% (343/2831) from 2005 to 2007 respectively. The weekly isolating rates changed accordantly with the trend of the percentages of ILI. The proportions of influenza H3N2 virus were 25.46% (28/114) and 2. 83% (6/212) in 2005 and in 2006 respectively,but the proportion increased to 62. 68% (215/343), which indicated that H3N2 virus became the predominant strain in 2007. Phylogenetic clustering analysis of influenza H3 N2 virus revealed that there were 5 elades. The viruses which were isolated in 2005 contained in the clade Ⅰ and Ⅱ,the viruses in 2006 were comprised in clade Ⅲ, and clade Ⅳ and Ⅴ included the viruses isolated in 2007. Although the stem of cladogram developed with one accord of the time isolated viruses, the viruses which were similar to vaccine strains had circulated in Shenzhen before a given strain was determined as vaccine strain by WHO. It was also noticed that more amino acid changes at antigenic sites,especially at sites A and B in the H3N2 viruses,were found in 2007 than that in 2005 and in 2006. But the sequences at the receptor-binding sites and disulphide bond sites were conserved and no new circulating strain for genetic reassortment had been found in the period. Conclusion Shenzhen might be one of areas where the ongoing genetic drift of influenza H3N2 viruses appeared earlier in China. The changes of influenza H3N2 virus showed the active status in the population. The results suggested that monitoring seasonal influenza viruses by sequence analysis could provide important and timely information on the appearance of strains with epidemiologic significance.