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.