RESUMEN
Sarcocystosis is a parasitic disease caused by intracellular coccidian protozoans that belong to the genus Sarcocystis. These parasites can cause diseases of the nervous system, abortion and economically significant losses in host animals. Previous studies have reported that Sarcocystis is found in mammals, birds and reptiles, while molecular and morphological studies of infected Tibetan sheep have not been performed in the Qinghai region. The aim of this study was to determine the prevalence of Sarcocystis spp. in Tibetan sheep in Qinghai, northwestern China. The results showed that in 1155 samples, sarcocysts from unspecified species were found in 50% (577/1155) of the sheep tissues by microscopy detection. The positive rates of sarcocysts in the diaphragmatic, esophageal and cardiac muscles were 78.4% (175/223), 29.1% (207/711), and 88.2% (195/221), respectively. Ultrastructural features were exclusively observed in Sarcocystis gigantea in the esophageal tissues. The specific architecture was characterized as a space between the two layers of the original capsule wall, which was filled with fiber bundles and tissue fluid. Cauliflower-like protrusions of the original capsule wall were observed toward the outer surface of the capsule. Prominent protrusions contained fibers and matrix. In addition, the Sarcocystis 18S rRNA genes from 6 esophageal tissue samples were cloned, sequenced, and aligned to related sequences from GenBank. All 5 S. gigantea sequences examined in this study were grouped into the same cluster and belonged to the same genotype. The other 5 Sarcocystis tenella sequences were obtained from cardiac muscle and diaphragm muscle and belonged to the same clade. Overall, this study revealed a high infection rate of Sarcocystis in Tibetan sheep in the region. The results of this study may provide a reference for further research investigating the sarcocystosis epidemic in Qinghai, China.