云南省边境地区哨兵牛芒市病毒的分离与鉴定

    Isolation and identification of Mangshi virus in sentinel cattle from border areas of Yunnan Province

    • 摘要:
      目的  掌握云南省边境地区动物虫媒病毒的多样性分布和传播风险。
      方法  在云南省景洪市设立哨兵牛3头,每周1次采血进行虫媒病毒的监测与分离。通过电镜观察、基因组琼脂糖凝胶电泳、RT-PCR与克隆测序对分离病毒进行鉴定,采用实时荧光定量RT-PCR与血清中和试验对病毒在动物上的感染进行回溯分析。
      结果  2019年,在监测期第13周,从1头哨兵牛的血液中分离出1株致C6/36细胞病变的病毒(V301/YNJH/2019),电镜观察可见直径约70 nm、呈二十面体对称结构的病毒粒子,琼脂糖凝胶电泳显示病毒基因组为双链RNA,RT-PCR鉴定分离毒株为芒市病毒(MSV)。测序显示,分离毒株的基因节段Seg-4和Seg-7长度为2 055和1 122 bp,编码病毒的外层衣壳蛋白VP4(628 aa) 和VP7(298 aa),基因节段Seg-2和Seg-9长度为3 055和1 076 bp,编码病毒的内层衣壳蛋白VP2(956 aa) 和VP9(283 aa);分离毒株与云南省芒市分离的MSV/DH13M041毒株具有最近的亲缘关系,核酸序列相似度在97.4% (Seg-9)~98.5% (Seg-2)之间,氨基酸序列相似度在96.4%(VP9)~98.4%(VP2)之间。病毒感染的回溯分析显示,监测期的第11周,牛血液中病毒核酸检测呈阳性,病毒核酸含量在第13周达到高峰,随后快速降低,在第18周转为阴性;感染哨兵牛在监测期的第13周已产生特异性中和抗体(1∶14),在第16~18周处于高峰(1∶226),至监测结束的第24周降低为1∶57。
      结论  本文从牛体中分离到了MSV,表明牛是MSV的易感动物之一,病毒在感染牛上呈“一过性感染”的特征。研究结果为进一步开展MSV的检测诊断、流行病学调查与致病性研究奠定了基础。

       

      Abstract:
      Objective  To analyze the diversity, dissemination risk of animal arboviruses in border areas of Yunnan Province.
      Method  Three sentinel cattles were placed in Jinghong City, Yunnan Province and blood samples were weekly collected for arboviruses monitoring and virus isolation. The isolated virus was identified through agar-gel electrophoresis, electron microscopy, RT-PCR amplification, cloning and sequencing. The infection characteristics of the virus in infected cattle were retrospectively analyzed by qRT-PCR and serum neutralizing test (SNT).
      Result  In 2019, a virus strain (V301/YNJH/2019) which caused cytopathic effect on C6/36 cells, was isolated from blood sample collected from one of the cattle at the 13th week of monitoring period. Electron microscope observation revealed that the virions were icosahedral symmetry with a diameter of about 70 nm. The result of agar-gel electrophoresis showed that the viral genome was composed of double stranded RNA. The isolated virus was identified as Mangshi virus (MSV) by RT-PCR identification. Sequence analysis exhibited the lengths of Seg-4 and Seg-7 from the isolated virus were 2 055 and 1 122 bp respectively, encoding viral out-most shell VP4 (628 aa) and VP7 (298 aa) proteins, while Seg-2 and Seg-9 were 3 055 and 1 076 bp respectively in length encoding viral inner-core VP2 (956 aa) and VP9 (283 aa) proteins. Phylogenetic analysis showed that the isolated virus had the closest relationship with MSV/DH13M041 isolated from Mangshi of Yunnan Province, with their nucleic acid sequence similarities ranging from 97.4% (Seg-9) to 98.5% (Seg-2) and amino acid sequence similarities ranging from 96.4% (VP9) to 98.4% (VP2). Retrospective investigation results of the virus infection indicated that virus nucleic acid was first detected in the blood of the infected cattle at the 11th week of monitoring period. The virus nucleic acid in the blood reached the peak at the 13th week and dropped rapidly, becoming not detectable within 5 weeks. The results of SNT showed that neutralization antibody against V301/YNJH/2019 was first detected at the 13th week (antibody titer 1∶14), peaked from the 16thto 18thweek (antibody titer 1∶226) and decreased to 1∶57 when monitoring terminated at the 24thweek.
      Conclusion  The MSV isolation from cattle indicating cattle is one of the susceptible animals of MSV. In naturally infected cattle, the virus is characterized by “transient infection” with no clinical symptoms. Our study imparts a foundation for study of epidemiology, pathogenicity, and diagnostic reagents of MSV.

       

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