Molecular Characteristics and Evolutionary Analysis of the Spike Protein Gene of Bovine Torovirus Strain from Yunnan
[Objective]This study was aimed to investigate the prevalence of Bovine torovirus(BToV)and the genetic evolution of the S gene in cattle herds in some areas of Yunnan province.[Method]655 faecal samples were collected from cattle of different ages from 15 cattle farms in 13 regions of Yunnan province,and BToV was detected by RT-PCR.6 representative positive samples were subjected to the S gene amplification,cloning,sequencing and genetic evolution analysis.[Result]RT-PCR results showed that there were 71 BToV positive samples were detected for the 655 samples with a total detection rate of 10.8％.The detection rate of diarrhea and non-diarrhea samples were 21.2％(59/278)and 3.2％(12/377),respectively.The detection rate of the samples from cattle at 1 week old,1 week to 1 month old,1 to 6 months old,and over 1 year old were 15.0％(3/20),17.7％(20/113),14.0％(45/321)and 1.5％(3/201)respectively.The results of similarity analysis showed that the six S gene sequences with a nucleotide similarity from 96.0％to 99.8％,and nucleotide similarity with the original strain Breda1 was from 94.7％to 96.0％.The similarity with domestic epidemic strains was 95.2％to 99.7％.Genetic evolutionary analysis showed that the six S gene were not in the same branch with the original strain Breda1,and formed a branch with the domestic strains in Sichuan and Henan as well as the Turkish strains,indicating that the BToV strains prevalent in Yunnan province were consistent with those of the currently prevalent strains in China,and that they were closely related to the domestic strains.Amino acid mutation site analysis showed that there were a small number of unique amino acid mutation sites of S gene in Yunnan province.The results of recombination analysis showed that BTOV-China/YN03-2021,BTOV-China/YN01-2021 and BTOV-China/YN06-2022 were predicted to be recombinant sequences,in which BTOV-China/YN06-2022 had the highest recombination score,with recombination region was located in 1 438 to 1 609 bp,and the main parent was strain BTOV-China/YN05-2021.The recombination region of BTOV-China/YN03-2021 was located in the 1 668 to 3 569 bp region,and the main parent was the Turkish strain BToV-HT2-TUR.The recombination region of BTOV-China/YN01-2021 was located in 261 to 2 552 bp,and the main parent was the Turkish strain BToV-HT2-TUR.The results of gene selection pressure analysis showed that the evolutionary mode of S gene was mainly dominated by neutral selection,there were the influence of purifying selection and positive selection pressure,too.[Conclusion]This study revealed that BToV had existed in Yunnan province cattle populations and the situation of prevention and control was relatively serious,which provided a reference for the study of epidemiology for BToV and the genetic evolutionary relationship of the spike protein gene in China,as well as a theoretical basis for the development of preventive and control measures for BToV infection in Yunnan province.
万方数据
维普
