First identification of Sarcocystis medusiformis in Chinese sheep (Ovis aries): Morphological and molecular characterization

This study reports the first detection of Sarcocysits medusiformis in sheep ( Ovis aries ) in China through integrated morphological and molecular analysis. Macroscopically visible S. medusiformis sarcocysts were found in 4 of 92 examined sheep (4.3%), measuring 2490–4796 × 248–405 µm and exhibiting thin, striated walls (1–2 µm thick). Ultrastructural examination revealed trapezoidal villar protrusions covering the cysts, each lined with an electron-dense layer, with scattered microtubes extending from the apex to the base. Molecular characterization was performed by amplifying and sequencing four genetic markers (18S rRNA, 28S rRNA, ITS-1, and mitochondrial cox1 ). The newly obtained 18S rRNA, 28S rRNA and cox1 sequences exhibited 100% identify with previously published S . medusiformis sequences in GenBank. Phylogenetic analysis based on these sequences consistently grouped S. medusiformis , S. gigantea , and S. moulei within a distinct clade. To date, S. medusiformis sarcocysts have been documented primarily in sheep, with a single known case in an addax ( Addax nasomaculatus ). Further investigations involving expanded sampling of wild and domestic bovid ruminants are needed to clarify the epidemiology, host specificity, and phylogenetic relationships of S. medusiformis and morphologically similar species.