Sarcocystis gracilis-like sarcocysts in a sheep

COCCIDIA of the genus Sarcocystis are obligate two-host parasites. Generally, the definitive host is a carnivorous animal, which becomes infected by ingesting sarcocysts encysted in the tissues of an intermediate host. After the definitive host becomes infected, sporocysts are shed in its faeces. Sarcocystis gracilis (Ratz 1909), together with Sarcocystis capreoli and Sarcocystis sibirica, are agents of sarcocystosis in roe deer (Capreolus capreolus), and dogs and foxes are recognised as definitive hosts. Four species of Sarcocystis have been described in sheep: Sarcocystis gigantea, Sarcocystis medusiformis, Sarcocystis tenella and Sarcocystis arieticanis. The definitive hosts of the first two species are felids, while canids serve as definitive hosts of the other two (Dubey and others 1989). Among the taxonomic criteria for the identification of Sarcocystis species, the structure of the sarcocyst wall is the most valuable. Dubey and others (1989) grouped Sarcocystis species into 24 types based on the villar protrusions of the cyst wall. For instance, the Sarcocystis species known to occur in sheep can be distinguished on the basis of the morphology of their villar protrusions, and are classified as type 21 (S gigantea), with cauliflower-like protrusions, type 20 (S medusiformis), with snake-like protrusions, type 14 (S tenella), with palisade-like protrusions, and type 7 (S arieticanis), with hairlike protrusions. This short communication describes the occurrence of an unusual species of sarcocyst found in a naturally infected sheep in Sicily, Italy. The structure of its cyst wall most resembled that of S gracilis described in roe deer (Entzeroth 1985, Dubey and others 1989).