A RAPD-PCR derived marker can differentiate between pathogenic and non-pathogenic Sarcocystis species of sheep.

Random amplified polymorphic DNA (RAPD)-PCR was used to differentiate among four cyst-forming coccidia of sheep, Sarcocystis tenella, Sarcocystis gigantea, Sarcocystis arieticanis, and Toxoplasma gondii. Genomic DNA of the four parasite species was amplified using RAPD-PCR and the DNA fragments were separated on agarose gels. A RAPD-PCR band derived from S. tenella was isolated from the gel and subcloned into pUC18. The insert was sequenced and found to be 1278 nucleotides long. This sequence appeared to be cryptic in nature as it showed no significant sequence peculiarities or similarity with any other known sequences either at the nucleotide or derived amino acid levels. The recombinant plasmid was radiolabelled and used as a probe in Southern hybridization. This probe, termed pSTF10, hybridised to Mbo I restricted genomic DNA of S. tenella and S. arieticanis, but not to DNA of S. gigantea, T. gondii, mouse, or sheep. It is likely that STF10 will become a valuable diagnostic tool for Sarcocystis infections in sheep to differentiate between pathogenic species of this genus and S. gigantea or T. gondii.