Redescription and molecular characterization of sarcocysts of Sarcocystis cymruensis from Norway rats ( Rattus norvegicus ) and Sarcocystis ratti from black rats ( R. rattus ) in China

In the present study, sarcocysts of Sarcocystis cymruensis were found in four of 42 (9.5%) Norway rats and those of S . ratti were observed in six of 60 (10%) black rats in China. With light microscopy, the sarcocysts of the two parasites were microscopic, and had smooth, thin cyst walls (≤ 1 μm). Ultrastructurally, the sarcocysts of S . cymruensis had small, osmiophilic, bleb-like protrusions, similar to type 1c; those of S . ratti had a cyst wall with regular, short, conical protrusions, similar to type 1 g. Three loci, i.e., 18S rDNA, the mitochondrial cox1 gene ( Cox1 ), and the mitochondrial Cytb gene ( Cytb ), of the two parasites were sequenced and analyzed, and the Cytb sequences of the two parasites constituted the first records of this marker in GenBank. A comparison of the newly obtained sequences of the three loci between the two parasites revealed that the interspecific similarities of 18S rDNA, Cox1 , and Cytb were 96.4–97.2%, 96.5%, and 93.7%, respectively. Therefore, the two species could be better discriminated with Cytb than with 18S rDNA and Cox1 . Phylogenetic analysis based on 18S rDNA sequences and Cox1 sequences indicated that the two parasites had a close relationship with Sarcocystis in nonruminant animals, especially birds and canids.