Prevalance, Morphology, and Molecular Characterization of Sarcocystis heydorni Sarcocysts from Cattle (Bos Taurus) in China.

Cattle are intermediate hosts for 2 zoonotic species of Sarcocystis, Sarcocystis hominis and Sarcocystis heydorni. Here we report S. heydorni from cattle for the first time in China. Sarcocysts of S. heydorni were found in muscle from 173 of 1,630 (10.6%) cattle in abattoirs (9.7% in skeletal muscles, 3.4% esophagus, 2.5% diaphragm, and 0.1% tongue; heart muscle was negative). By means of light microscopy, S. heydorni sarcocysts were thin-walled (<1 μm). Using transmission electron microscopy, the sarcocyst wall had short (0.3-0.5 × 0.5-0.9 μm) stubby protrusions, the tips of which contained electron-dense, disk-shaped plaques, similar to the sarcocyst wall type 29b. In preliminary transmission attempts, a human volunteer did not excrete sporocysts in feces after ingesting 579 sarcocysts S. heydorni isolated from cattle. Phylogenetic analysis using the 2 molecular markers (18S rRNA gene and mitochondrial cox1 gene) indicated S. heydorni shared the closest affinity with species of Sarcocystis, which employ ruminants as intermediate hosts and canids as definitive hosts.