摘要目的:分析2023年8月山东1例儿童输入相关性D8基因型麻疹病例的流行病学、病原学特征及传播途径。方法:将2023年8月山东省监测到的儿童麻疹病例纳入研究，对该病例及接触者16名调查对象开展现场流行病学调查（近期暴露史、既往免疫史等）。同时采集16名调查对象的血清和咽拭子标本，采用ELISA方法进行麻疹IgM、IgG抗体及抗体亲和力检测，采用荧光定量PCR及RT-PCR方法进行麻疹病毒核酸检测及基因型别鉴定，采用MEGA、Beast等软件对获得的基因序列进行遗传进化特点分析。结果:病例为11岁男童，五年级学生，2023年8月28日发病；共调查密切接触者5名，其中家庭成员3名（爷爷、父亲和姐姐），玩伴2名；同时调查了在病例传染期（出疹后5 d）内与姐姐有密切接触的同学11名。16份血清标本中，除病例IgM为阳性外，其他15份血清标本均为IgM阴性。血清抗体亲和力检测结果显示：16份血清标本中，有14份标本IgG阳性，其中8份相对亲和力指数>55%，为高亲和力抗体；1份相对亲和力指数<45%，为低亲和力抗体；5份亲和力为45%~55%；病例姐姐和爷爷的IgG检测OD值均高于其他接触者。基于研究对象的疫苗接种史和IgM、IgG检测结果，初步判定病例为麻野病毒近期感染，病例姐姐和爷爷曾经有过麻疹野病毒感染史，其他接触者的高亲和力抗体可能是由麻疹疫苗诱导产生。16份咽拭子标本检测结果显示，仅病例的麻疹病毒核酸阳性，其余15份标本均为麻疹病毒阴性。遗传进化分析结果显示：本病例病毒序列与2023年8月香港株序列一致性为100%；与2018—2019年山东省出现的D8基因型分属于不同的传播链，其序列一致性为98.0%~98.8%。病例所在传播链上的序列一致性为99.1%~100%，该传播链的进化速率约为8.38×10 -3［碱基替换/（位点·年 -1）］，最新共同祖先大约出现在2011年。 结论:该病例为山东省首例儿童输入相关性D8基因型麻疹病例；该病例与2018—2019年山东省输入的D8基因型成人病例不存在时空关联，为一起新的D8基因型输入疫情。

abstractsObjective:To analyze the epidemiological, etiological characteristics and transmission of an imported D8 genotype measles case in a child in Shandong Province, August 2023.Methods:A study was conducted on a measles case and 16 contacts in Shandong Province in August 2023. Field epidemiological surveys, including recent exposure and immunization history, were conducted. Serum and throat swab samples were collected from all 16 subjects. Measles IgM and IgG antibody levels and avidity were measured by ELISA, while virus detection and genotyping were performed using fluorescence quantitative PCR and RT-PCR. Genetic evolutionary analysis of the obtained sequences was conducted using MEGA and Beast software.Results:The case was an 11-year-old boy, a fifth-grade student, who developed symptoms on August 28, 2023. A total of five close contacts were investigated, including three family members (grandfather, father and sister) and two playmates. Additionally, 11 classmates who had close contact with the case′s sister during the infectious period (within five days after the rash onset) were also investigated. Among the 16 serum samples tested, only one case was positive for IgM, while the other 15 samples were negative for IgM. The results of the serum antibody avidity test showed that among the 16 serum samples, 14 were positive for IgG. Of these, eight had a relative avidity index >55%, indicating high-avidity antibodies; one had a relative avidity index <45%, indicating low-avidity antibodies; and five had an avidity index between 45% and 55%. The IgG detection OD values for the case′s sister and grandfather were higher than those of the other contacts. Based on the vaccination history of the subjects and the results of IgM and IgG tests, it was preliminarily determined that the case had a recent wild-type measles virus infection. The case′s sister and grandfather had a history of measles wild-type virus infection, while the high-avidity antibodies in the other contacts were likely induced by the measles vaccine. The results of the pharyngeal swab tests showed that only the case was positive for measles virus nucleic acid, while the remaining 15 samples were negative for measles virus. The genetic evolutionary analysis revealed that the viral sequence of this case (Mvs/Shandong.CHN/38.23) had a 100% homology with the Hong Kong strain sequence from August 2023. It belonged to a different transmission chain from the D8 genotype strains that appeared in Shandong Province between 2018 and 2019, with sequence homology ranging from 98.0% to 98.8%. The sequence homology within the transmission chain of this case was between 99.1% and 100%. The evolutionary rate of this transmission chain was approximately 8.38×10 -3 sub/site/year, and the most recent common ancestor was estimated to have emerged around the year 2011. Conclusion:This case is the first imported D8 genotype measles case in Shandong Province. There is no spatio-temporal correlation between this case and adult cases of D8 genotype imported from Shandong Province in 2018-2019, indicating a new D8 genotype imported epidemic.