Sarcocystis tupaia, sp. nov., a new parasite species employing treeshrews (Tupaiidae, Tupaia belangeri chinensis) as natural intermediate hosts

The range of vertebrates that serve as intermediate hosts for parasites in the genus Sarcocystis remains incompletely defined. Here, we provide the first report of infections in treeshrews, describe the morphology of encysted parasites using light and transmission electron microscopy, and place this agent within a phylogenetic context by sequencing and comparing its 18 S ribosomal DNA to that of related parasites. Muscle infections were diagnosed in four of 45 wild treeshrews captured in the vicinity of Kunming, Yunnan Province, Mainland China. Thread-like cysts (10.773 ± 2.411 mm in length, 0.106 ± 0.009 mm in width) had walls (0.538–0.746 µm thick) that lacked perpendicular protrusions. The interior of the cyst was packed full with cyst merozoites, the shape of which was typical of Sarcocystis. The primary cyst wall consisted of a thin membrane supported by osmiophilic material, 31–60 nm in thickness. The ground substance was about 105–526 nm thickness. Cysts conformed to typical of ‘type 1’ sarcocysts. Freshly examined and frozen specimens did not differ in their cyst wall structure, however, the appearance of bradyzoites did differ: the conoid, rhoptries and micronemes were all visible in fresh bradyzoites; in stored bradyzoites, by contrast, the rhoptries appeared smaller, and although the conoid was visible, the micronemes were not. 18 S rRNA gene was distinct from any previously reported sequence in GenBank. Their genetic and morphological uniformity suggest that these parasites, derived from treeshrews, represent a single biological species, Sarcocystis tupaia, sp. nov.