First identification of Sarcocystis arctica in captive cheetahs (Acinonyx jubatus) in China with annotations on closely related species in carnivore intermediate hosts

Abstract Background Sarcocystis spp. are cyst-forming, intracellular protozoan parasites that are transmitted between hosts linked through a predator-prey relationship. There was only one previous report describing cysts of Sarcocystis in the musculature of cheetahs (Acinonyx jubatus), and the species was designated to be S. felis because of morphological similarity to this species. However, no nucleotide sequences of genetic markers for the parasite in cheetahs are presently provided to serve as references. Methods Light microscopy (LM) and transmission electron microscopy (TEM) were used to morphologically characterize the sarcocysts isolated from muscular tissues of cheetahs died in zoos in Zhengzhou city, China. Meanwhile, four marker genes (nuclear 18S rRNA, 28S rRNA, ITS-1, and mitochondrial cox1) of the sarcocysts were amplified, sequenced and analyzed. Results Only one type of sarcocyst was observed in two out of six cheetahs. Under LM, the sarcocyst wall was striated and 1.4–2.3 µm thick. Ultrastructurally, the wall had irregular-shaped, small villous protrusions resembling wall type 9c, similar to those of S. arctica, S. caninum and S. felis. Molecularly, the samples shared their highest identity values with those of S. arctica and S. caninum: 99.9–100% and 99.8–100% (18S rRNA), 99.5% and 99.3–99.5% (28S rRNA), 95.9–97.5% and 96.3–97.3% (ITS-1), and 99.6% and 99.2–99.7% (cox1), respectively. Compared to ITS-1 of S. felis, identities ranged between 87.5% and 88.9%. Phylogenetic reconstruction revealed the newly-sequenced Sarcocystis clustered with S. arctica and S. caninum, whereby S. felis (ITS-1) and S. canis (ITS-1, 18s rRNA, cox1) were sister species. Conclusions We regard the Sarcocystis samples to represent S. arctica, which is the first record of a Sarcocystis species believed specific for canids as intermediate hosts to infect a feline host. The occurrence of S. arctica in a feline carnivore suggests a broader intermediate host range for this Sarcocystis species for which predatory birds are likely definitive hosts. Furthermore, our study supports the notion that S. caninum is conspecific with S. arctica.