Ultrastructural and Molecular Identification of the sarcocysts of Sarcocystis tenella and Sarcocystis arieticanis Infecting Domestic Sheep (Ovis aries) from Egypt.

Comparative analyses of the sequences of the four genetic markers (18S rRNA, 28S rRNA, mitochondrial cox1 and ITS-1) for S.tenella and S.arieticanis isolates detected herein, revealed genetic variations of 95% and 95- 96% among the different isolates on the level of the 18S rRNA and 28S rRNA, respectively. Whereas, the cox1 and ITS-1 shared sequence identities of 76-78% and 70-73%, respectively. S.tenella was strongly related to S.capracanis infecting goats (Capra hircus). Sequence identity of 98% on the level of 18S rRNA, 28S rRNA genes was observed between the currently identified isolates of S.tenella and the formerly GenBank deposited isolates of S.capracanis. While, cox1 sequences shared identities of 92-93%. Furthermore, S.arieticanis isolates identified here were closely related to the formerly published sequences of S.hircicanis. The 18S rRNA and 28S rRNA sequences of S.arieticanis shared 98% and 94-95% identities with those of S.hircicanis, respectively. However, 87-88% homologies were observed between the cox1 sequences of S.arieticanis and S.hircicanis. Consequently, cox1 and ITS-1 gene sequences act as better genetic markers than 18S rRNA and 28S rRNA sequences for the characterization of ovine Sarcocystis spp. Maximum parsimony analyses based on the sequences of three genetic markers, (18S rRNA, 28S rRNA and mitochondrial cox1), yielded the same placement of the currently identified isolates of the two taxa (S.tenella and S.arieticanis) within a clade of Sarcocystis species with carnivorous animals as known, or assumed, final hosts.