Morphological and Molecular Characterization, and Demonstration of a Definitive Host, for Sarcocystis masoni from an Alpaca (Vicugna pacos) in China

Simple Summary Sarcocystis spp. are cyst-forming intracellular protozoan parasites characterized by a two-host prey-predator life cycle. The alpaca (Vicugna pacos) is one of the South American camelids (SACs), and in recent years, this animal was introduced to China to be raised for its meat, skin, and wool and to be kept as tourist attractions and as pets. There is considerable confusion regarding the classification and nomenclature of the species of Sarcocystis in SACs. Two Sarcocystis species, named S. auchenia and S. masoni, are currently regarded as valid in SACs based on sarcocyst morphology and 18S rDNA sequences. However, the definitive host of S. masoni remains unknown. Here, S. masoni sarcocysts in an alpaca were morphologically described and molecularly characterized. Furthermore, the life cycle of S. masoni was completed via experimental animal infection. The present analysis showed that S. masoni has a close relationship with S. cameli in the dromedary camel (Camelus dromedaries), and the relationship between the two parasites needs to be clarified in the future. Only 18S rDNA sequences of Sarcocystis spp. in South American camelids (SACs) are deposited in GenBank as references, and the definitive host of S. masoni in SACs is still unclear. Here, S. masoni sarcocysts detected in an alpaca (Vicugna pacos) in China were investigated with the aid of light (LM) and transmission electron (TEM) microscopy, and characterized using four genetic markers, i.e., 18S rDNA, 28S rDNA and ITS, and the mitochondrial cox1. Additionally, the life cycle of the parasite was completed via experimental animal infection. Under LM, S. masoni sarcocysts exhibited numerous 1.3-2.1 mu m conical protrusions. Under TEM, the sarcocyst wall contained conical, cylindrical, or irregular-shaped villar protrusions, similar to type 9j. Two dogs (Canis familiaris) fed S. masoni sarcocysts shed sporocysts with a prepatent period of 8-9 days. The newly obtained 18S rDNA sequences showed 98.4-100% identity with those of S. masoni in SACs previously deposited in GenBank. Interestingly, the newly obtained sequences of 18S rDNA and mitochondrial cox1 shared 99.6-100% and 98.2-98.5% identity, respectively, with those of S. cameli in dromedary camels (Camelus dromedaries). Phylogenetic analysis based on sequences of 18S rDNA, 28S rDNA, or mitochondrial cox1 revealed that S. masoni has a close relationship with Sarcocystis spp. in ruminants. The relationship between S. masoni and S. cameli deserves to be further clarified in the future.