Microscopic and Molecular Identification of Sarcocystis spp. in Intestines of Canids and Mustelids Associated with Sarcocyst-Forming Species in Rodent Muscles

Sarcocystis, a diverse and species-rich protist genus infecting reptiles, birds, and mammals, remains poorly understood in terms of true diversity and their lifecycles. Typically, sarcocysts are found in the muscle tissue of the intermediate host (IH), while oocysts undergo sporulation in the intestines of the definitive host (DH). Rodent-associated Sarcocystis species often form cryptic species complexes with strong specificity to their DHs; however, their presence in the intestines of wild carnivores, whose IHs are rodents, is understudied. The aim of this study was to investigate the distribution of rodent-associated Sarcocystis species in the intestines of wild Mustelidae and Canidae from Lithuania using light microscopy (LM) and nested PCR targeting 28S rRNA. LM analysis of intestinal scraping revealed Sarcocystis spp. in 56.3% of canids and mustelids, while DNA sequence analysis identified 41.0% of mustelids and 11.6% of canids as positive. Three Sarcocystis species, S. arvalis, S. myodes, and S. ratti, and the genetic lineage Sarcocystis sp. Rod8, which belong to the same cryptic species complex, were identified in mustelids, while S. arvalis and S. myodes were detected in canids. Thus, mustelids contribute more than canids to the natural transmission of Sarcocystis spp. from rodents in Lithuania.