Isolation and genetic characterization of epizootic hemorrhagic disease virus serotype 1 strains prevalent in China from 2013 to 2019

【Objective】 Mastering the prevalence and genetic characteristics of epidemic hemorrhagic disease virus (EHDV) serotype 1(EHDV-1) strains in southern China provides basis for developing EHDV-1 serotype specific diagnosis methods, epidemiology investigation and pathogenicity research.【Method】 Cattle and sheep arbovirus monitoring sites and sentinel cattle were set up in Yunnan, Guangdong and Guangxi from 2013 to 2019. Animal blood samples were collected regularly for arbovirus isolation. The serotypes of isolated EHDV strains were determined by neutralization test, and the genomic segments(Seg-2, Seg-3 and Seg-6) of the isolated EHDV strains were amplified using RT-PCR, bidirectionally sequenced and analyzed. BioEdit was used to calculate the identities of the nucleotide and deduced amino acid sequences.【Result】 A total of 33 EHDV strains were isolated from sentinel animals between 2013 and 2019 in Yunnan, Guangdong and Guangxi, including 7 EHDV-1 strains. Sequence analysis showed that the Seg-2, Seg-3 and Seg-6 nucleotide sequences of EHDV-1 strains isolated from Yunnan, Guangdong and Guangxi sharedhigh similarty, with average sequence identities of(97.65±1.51)%, (94.87±4.72)% and(97.61±1.41)%, respectively. The average sequence identities of the corresponding deduced amino acid sequences were(97.69±1.36)%, (99.49±0.32)% and(97.51±2.47)%, respectively. The phylogenetic trees based on nucleotide sequence similarity of Seg-2, Seg-3 and Seg-6 indicated that EHDV-1 strains could be divided into Eastern and Western topotypes. The Eastern topotype strains were usual-ly isolated from China, Japan and Australia, while the Western topotype strains mainly came from America and Africa. The phylogenetic trees based on nucleotide sequence similarity of Seg-2 indicated that the 7 EHDV-1 strains belonged to the Western topotype and formed an independent evolutionary branch on the phylogenetic tree. The phylogenetic trees based on nucleotide sequence similarity of Seg-3 indicated that the 7 EHDV-1 strains belonged to Eastern-1 and Eastern-2 sub-topotypes, and shared the closest relationship with Japanese EHDV-1 and EHDV-6 strains, respectively. The phylogenetic trees based on nucleotide sequence similarity of Seg-6 indicated that the 7 EHDV-1 strains belonged to the Eastern topotype branch, and possessed the closest relationship with EHDV-1 strains isolated from Japan.【Conclusion】 The EHDV-1 strains are widely prevalent in southern China. Seg-2 and Seg-6 sequences of EHDV-1 strains prevalent in southern China had the most recent common ancestor, respectively, while Seg-3 comes from different ancestral viruses. The emergence of Western topotype Seg-2 in EHDV-1 strains isolated from China indicatesthat Western topotype strains have reassorted with the local epidemic EHDV-1 strains after invading China, suggesting that the EHDV-1 strains prevalent in China are reassortant strains of the Western and the Eastern topotypes. The study provides a warning to prevent the invasion of highly pathogenic Western topotype strains into China and causing severe economic losses in animal industry.