Abstract
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.