Isolation and genetic characteristics of epidemic hemorrhagic disease virus serotype 6 (EHDV-6) strains from Yunnan and Guangdong Provinces

Objective  To isolate epidemic hemorrhagic disease virus serotype 6 (EHDV-6) strains prevalent in southern China, and investigate the genetic characteristics of the isolated strains.

Method  Blood samples were collected from sentinel animals in Yunnan and Guangdong Provinces in China. EHDV infection was monitored and the virus was isolated. The serum types of isolated strains were determined by serum neutralization test, and segments 2, 3 and 6 (Seg-2, -3 and -6) of EHDV-6 isolated strains were amplified by one-step RT-PCR and subsequently sequenced.

Result  From 2012 to 2016, 25 EHDV strains were isolated from sentinel animals in Yunnan and Guangdong Provinces and 11 strains of them were EHDV-6. Seg-2, -3 and -6 of Chinese EHDV-6 strains were of Eastern topotype, and the nucleic acid sequence similarities were 99.1%, 98.9% and 98.8% respectively, which were clustered into an independent Chinese branch on the phylogenetic tree. Chinese EHDV-6 strains had the closest relationship with the EHDV-6 strains which caused epidemic outbreaks in Japan. The Japanese EHDV-6 strain was within the Chinese branch on the phylogenetic tree. The similarities of nucleic acid sequences of Seg-2 and Seg-3 between the Japanese and Chinese strains were 98.5% and 93.9% respectively.

Conclusion  The sequences of EHDV-6 strains prevalent from Yunnan and Guangdong Provinces are highly similar. The closest genetic relationship between Japanese and Chinese EHDV-6 strains suggests that there may be flow of EHDV between China and Japan. The results provide a basis for further research on epidemiological analysis, pathogenicity, etiological diagnosis and vaccine preparation of EHDV-6 strains in China.