Abstract: [Objective] The aim of the present study was to characterize the prevalence and the subgenotype distribution of Blastocystis in yaks in Gonghe County, Qinghai Province. [Method] A total of 475 fresh fecal samples were collected from yaks raised in Sangde pasture （n=89）, Kanzhuoxiangmao pasture （n=12） and Zanla family pasture （n=374） in Gonghe County. All of the samples were subjected to fecal genomic DNA extraction. Nested PCR assay was performed to detect the presence of SSU rDNA of Blastocystis, and selected positive PCR products were subjected to bidirectional sequencing. The subgenotype identification of Blastocystis was conducted based on the sequence alignment of SSU rDNA, and the phylogenetic tree was constructed to assess the genetic evolutionary relationships. [Result] Among the 475 yak fresh fecal samples, 361 samples were positive for Blastocystis, with a total infection rate of 76.00% （361/475）. The Blastocystis positive samples were observed in Sangde pasture, Kanzhuoxiangmao pasture and Zanla family pasture, and the infection rates of the three pastures were 96.63% （86/89）, 91.67% （11/12） and 70.59% （264/374）, respectively. A total of 126 SSU rDNA fragments were sequenced and used to perform subgenotype identification of Blastocystis. The sequence alignment analysis demonstrated that there were 5 subgenotypes of Blastocystis. The highest detection rate was observed in ST10 subgenotype （80.95%, 102/126）, followed by ST26 （9.52%, 12/126）, ST25 （6.35%, 8/126）, ST21 （2.38%, 3/126） and ST5 （0.80%, 1/126） subgenotypes. [Conclusion] Blastocystis infection in yaks was common in Gonghe County, and the subgenotypes exhibited genetic diversity. A zoonotic subgenotype of ST5 was observed, indicating that the infection monitoring of Blastocystis in yaks in this region was expected to be enhanced.

Key words: yak, Blastocystis, subgenotype, molecular epidemiological survey, SSU rDNA