The genus Sarcocystis are worldwide distributed unicellular parasites known for their two-host prey-predator life cycle. Sarcocysts mainly develop in the muscles of the intermediate host (IH). Following ingestion of mature sarcocysts, they undergo sexual reproduction in the small intestines of the definitive host (DH), resulting in the formation of sporocysts which are subsequently excreted into the environment in conjunction with faecal matter. Even though sarcocystosis in the DH is usually asymptomatic, it can result in nausea, diarrhoea or weight loss. Globally, research efforts tend to concentrate on domestic dogs, cats, and other carnivores due to the challenges associated with studying grey wolves (Canis lupus), such as their lower population density and legal protections. Understanding the role of grey wolves in parasite transmission is crucial, particularly in regions where they serve as apex predators.

During 2021-2023, 13 intestinal samples from hunted grey wolves were collected in Lithuania and were analysed by the means of microscopy and molecular analysis. Light microscopy revealed that 92.3 % of the samples were positive for the presence of Sarcocystis spp. sporocysts and oocysts. A nested PCR assay targeting the cox1 gene was performed to confirm the presence of Sarcocystis DNA and identify the specific species involved. Molecular analysis revealed the presence of 12 different Sarcocystis species: S. arieticanis and S. tenella (IH: sheep), S. miescheriana (IH: pig and wild boar), S. capracanis (IH: goat), S.alces, S.capreolicanis, S.gracilis, S. hjorti, S. iberica, S. linearis, S. taeniata, and S. venatoria (IH: Cervidae).

Based on the variety of Sarcocystis species and high percentage of infected animals, the grey wolf plays an important role in transmission of these parasites.