Sporocysts of Sarcocystis bertrami (syn. Sarcocystis fayeri) shed by dogs: Molecular analysis, morphometry and pattern of excretion.

Sarcocystis bertrami (synonym: Sarcocystis fayeri) is a coccidian parasite that infects horses and donkeys in several countries. Dogs are known as definitive hosts of the parasite, however, the patent period is not well defined, and S. bertrami shed by dogs has never been confirmed by molecular methods. Here we investigated the shedding of S. bertrami by experimentally infected dogs and examined the excreted parasites by morphological and molecular tools. Three dogs of small breeds (one Yorkshire terrier and two miniature Pinschers) were acquired with ages of 30 and 60 days and were exclusively fed commercial dog food. Two dogs consumed equine muscle tissues containing cysts of S. bertrami. The third dog served as negative control and was simultaneously fed commercial dog food. The two animals that received equine tissues shed sporocysts and/or oocysts in their feces after prepatent periods of 13 and 23 days. The patent periods were 47 and 14 days. Sporocysts showed average dimensions of 14.19 µm (± 0.53) x 10.06 µm (± 0.44). The control dog did not shed sporocysts or oocysts of the parasite. Interestingly, patent periods had never been reported, and for one dog, the patent period (47 days) was longer than that reported for other Sarcocystidae parasites. PCRs to the gene 18S and to the internal transcribed spacer 1 (ITS1) of the rDNA were successfully performed with DNA extracted from sporocysts. ITS1 sequences were also obtained from the equine tissue cysts used to infect the dogs. Nucleotide sequences of cloned fragments of 18S from sporocysts, and ITS1 from both stages (tissue cysts and sporocysts) matched with S. bertrami (18S: 97.50-99.88 %; ITS1: 88.76-95.21 %), although high molecular diversity was observed with data from these loci. PCR to cox1 using sporocysts' DNA failed to amplify any product. The possibility of the existence of an additional and undescribed Sarcocystis species in the excreted sporocysts, besides S. bertrami, cannot be excluded from this experiment. To our knowledge, this is the first molecular confirmation of S. bertrami in canine feces. Sporocyst dimensions and prepatent periods observed in this study were similar to those previously described for S. bertrami and S. fayeri. In conclusion, the molecular, morphological and biological data generated here fit in previous descriptions for both S. bertrami and S. fayeri.