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

Abstract

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 μm 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.

Sarcocystis spp. of New and Old World Camelids: Ancient Origin, Present Challenges

“…For S. masoni , experimental infection has also determined that dogs can serve as a definitive host. In this case, the species of excreted oocysts was confirmed by PCR-RFLP analysis of the cytochrome c oxidase subunit I ( cox-1 ) gene [ 33 ].…”

“…Histological studies of the intestines of dogs fed with S. masoni - or S. aucheniae -infected SAC meat have shown that oocysts and sporocysts were mostly concentrated towards the tips of the villosities, without further alterations in the mucosa [ 32 , 33 ]. Gamogony was observed within the lamina propria of the intestines of puppies that had been fed with S. cameli -infected meat [ 38 ].…”

“…PCR amplification followed by sequencing of different molecular markers, such as the 18S and 28S ribosomal RNA (rRNA), cox-1 genes, and the ITS region, as well as PCR-RFLP of cox-1 or 18S rRNA genes, has been used for the identification and molecular characterization of SACs and OWCs Sarcocystis spp. [ 17 , 26 , 27 , 33 ]. These methods are not practical for diagnostic purposes and are meant to be applied to tissue or cyst samples obtained after necropsy.…”

“…Primers were designed to specifically amplify S. aucheniae DNA, avoiding cross-amplification of the DNA of Toxoplasma gondii or Neospora caninum , two closely related coccidians that also infect SACs [ 56 ]. In addition, the recent availability of whole-length 18S rRNA sequences of S. masoni has allowed for confirmation that these PCR detection protocols of S. aucheniae do not cross-react with other SAC-infecting Sarcocystis species [ 33 ].…”

“…Microscopic sarcocysts, referred to as Sarcocystis sp., S. lamacanis or, more recently, S. masoni , were reported in the cardiac muscle of llamas and guanacos from Argentina, alpacas from Peru, and alpacas bred in the extra-Andean countries China, Iran, and Australia [ 17 , 33 , 46 , 62 , 63 , 64 , 65 , 66 ]. Microcysts were, in some cases, also observed in other body locations in addition to the myocardium, such as liver, kidney, spleen, lung, tongue, and skeletal muscles [ 17 , 33 , 62 , 63 ].…”