Redescription of the sarcocysts of Sarcocystis rileyi (Apicomplexa: Sarcocystidae).

The intermediate hosts for Sarcocystis rileyi (Stiles 1893) Minchin 1913 are ducks (Anas spp.), and the striped skunk (Mephitis mephitis) is its definitive host. The structure of sarcocysts from an experimentally infected shoveler duck (Anas cylpeata) fed sporocysts from an experimentally-infected M. mephitis was studied and compared with type specimens from a naturally infected duck. The experimentally infected duck was killed 154 d after feeding sporocysts. By light microscopy the sarcocyst wall was 3-5 microm thick with indistinct villar protrusions. Ultrastructurally, the sarcocyst wall was a type-23 cyst wall with anastomosing villar protrusions that were up to 7.5 microm long. The villar projections contained filamentous structures. The bradyzoites were 12-14 microm long. Structurally, the sarcocyst from the naturally infected and experimentally infected ducks appeared similar.