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

This study reports the first identification of Sarcocysits medusiformis in sheep (Ovis aries) in China, based on integrated morphological and molecular analyses. Macroscopic S. medusiformis sarcocysts were detected in 4 of 92 sheep (4.3%), measuring 2490–4796 × 248–405 μm, and featuring thin, smooth walls (1–2 μm thick). Ultrastructurally, the cyst wall was covered by trapezoidal villar protrusions, each lined by an electron-dense layer and containing scattered microtubules extending from the apex to the base. Genetic characterization of three isolates targeted four markers: the nuclear 18 S rRNA, 28 S rRNA, and ITS-1 genes, and the mitochondrial cox1 gene. The ITS-1 sequences obtained here are the first reported for this species. Intraspecific identity among isolates was 100% for 18 S rRNA and 28 S rRNA, 99.7–100% for cox1, and 99.0–100% for ITS-1. BLAST analysis confirmed up to 100% identity with existing S. medusiformis sequences for 18 S rRNA, 28 S rRNA, and cox1. Phylogenetically, S. medusiformis consistently clustered with S. gigantea and S. moulei into a distinct, well-supported clade in analyses of 18 S rRNA, 28 S rRNA, and cox1. To date, S. medusiformis sarcocysts have been reported predominantly in sheep (subfamily Caprinae), with a single record in an addax (Addax nasomaculatus; subfamily Hippotraginae). Expanded surveillance of domestic and wild bovid ruminants is warranted to fully elucidate the epidemiology, host range, and phylogenetic relationships of S. medusiformis and related morphotypes.