Domestic cats (Felis catus) are definitive hosts for Sarcocystis sinensis from water buffaloes (Bubalus bubalis).

The definitive hosts of Sarcocystis sinensis in water buffaloes have hitherto been unknown, but the close similarity of this species to the cat-transmitted Sarcocystis bovifelis in cattle suggested they were felids. In a previous study, two domestic cats were fed macroscopic sarcocysts of Sarcocystis fusiformis contained within or dissected from the esophageal muscles of water buffaloes, while no microscopic sarcocysts of S. sinensis were noticed. Both cats started shedding small numbers of sporocysts 8-10 days post infection (dpi) and were euthanized 15 dpi. Using a PCR-based molecular assay targeting the mitochondrial cox1 gene of S. fusiformis, both cats were shown to act as definitive hosts for this species. In the present study, DNA samples derived from oocysts/sporocysts in the intestinal mucosa of both cats were further examined by PCR for the presence of S. sinensis using 2 newly designed primers selectively targeting the cox1 gene of this species. All 6 DNA samples examined from each cat tested positive for S. sinensis. A 1,038-bp-long portion of cox1 was amplified and sequenced as 2 overlapping fragments from 5 of these DNA samples. The 5 sequences shared 99.3-100% identity with 7 previous cox1 sequences of S. sinensis obtained from sarcocysts in water buffaloes. Additionally, amplification of the ITS1 region with primers targeting various Sarcocystis spp., yielded amplicons of 2 different lengths, corresponding to those obtained from sarcocyst isolates of S. sinensis and S. fusiformis, respectively. This is the first study to show that cats act as definitive hosts for S. sinensis.