Redescription and molecular characterization of sarcocysts ofSarcocystis cymruensisfrom Norway rats (Rattus norvegicus) andSarcocystis rattifrom black rats (R. rattus) in China

In the present study, sarcocysts ofSarcocystis cymruensiswere found in four of 42 (9.5%) Norway rats and those ofS.rattiwere 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 mu m). Ultrastructurally, the sarcocysts ofS.cymruensishad small, osmiophilic, bleb-like protrusions, similar to type 1c; those ofS.rattihad 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 mitochondrialCytbgene (Cytb), of the two parasites were sequenced and analyzed, and theCytbsequences 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, andCytbwere 96.4-97.2%, 96.5%, and 93.7%, respectively. Therefore, the two species could be better discriminated withCytbthan with 18S rDNA andCox1. Phylogenetic analysis based on 18S rDNA sequences andCox1sequences indicated that the two parasites had a close relationship withSarcocystisin nonruminant animals, especially birds and canids.