EPIDEMIOLOGICAL SIGNIFICANCE OF REASSORTMENT BETWEEN INFLUENZA C VIRUSES

众所周知，在体外，以RNA片段交换为特征的重配在两种不同的C型流感病毒株之间发生的频率很高。进行这项研究是为了获得关于丙型流感病毒基因重组在自然界中发生的频率的信息。两年来取得的成果总结如下：对先前分离的病毒株进行的抗原和寡核苷酸指纹分析提出了这样一种可能性，即一些分离株可能是由属于不同谱系的两种病毒重新组合而成的。比较他们七个RNA片段的部分核苷酸序列与参考株透露,奈良/ 1/85是一个继承了他和NP基因的重组从密西西比/ 80 (MS / 80)有关的病毒和其他五个基因从一个山形/ 81 -相关病毒,这三个菌株(山形/ 5/92,宫城县/ 3/93,宫城县/ 4/93)孤立在1992/93都是重组也收到他,P3, NP和M基因从一个女士/ 80 -如病毒和PB2, PB1,Yamagata/81样病毒的NS基因利用25株C型流感病毒株的核苷酸序列，构建了HE和M基因的系统发育树。两株树的比较结果表明，Yamagata/64、神奈川/1/76和宫城/77株都是接受青森/74样病毒HE基因和山形/81样病毒M基因的重组株。此外，MS/80样病毒和爱知/81样病毒在M基因上的进化关系比在HE基因上的进化关系更接近，这表明这两个病毒群可能是通过重组事件在遗传上相关的。基于这些结果，我们认为C型流感病毒之间的基因组重组在自然界中经常发生，因此有助于病毒的遗传变异。

It is well known that reassortment characterized by the exchange of RNA segment between two different influenza C strains occurs in vitro at a high frequency. This study was perfomed to obtain information on how often reassortment of influenza C virus genes occurs in nature. The results obtained in these two years are summarized as follows.1.Antigenic and oligonucleotide fingerprinting analyzes of the previously isolated virus strains raised the possibility that several isolates might have arizen by reassortment from two viruses belonging to different lineages. Comparison of the partial nucleotide sequences of their seven RNA segments with those of the reference strains revealed that Nara/1/85 is a reassortant which inherited the HE and NP genes from a Mississippi/80 (MS/80) -related virus and the other five genes from a Yamagata/81-related virus, and that three strains (Yamagata/5/92, Miyagi/3/93, Miyagi/4/93) isolated during 1992/93 are all reassortants which received HE,P3, NP and M genes from an MS/80-like virus and PB2, PB1, and NS genes from a Yamagata/81-like virus.2.Phylogenetic trees for the HE and M genes were constructed by using the nucleotide sequences of 25 influenza C strains. Comparison between these two trees showed tha strains Yamagata/64, Kanagawa/1/76, and Miyagi/77 are all reassortants which received HE genes from an Aomori/74-like virus and M genes from a Yamagata/81-like virus. It also became evident that the evolutionry relationship between MS/80-like and Aichi/81-like viruses was much closer for the M gene than the HE gene, raising the possibility that these two virus groups are genetically related by a reassortment event.3.Based on these results, we suggest that reassortment of the genome between influenza C viruses occurs in nature frequently and thus contributes to genetic variation of the viruses.