Fine structure of immature cysts of Sarcocystis cruzi.

Sarcocystis cruzi forms cysts in striated muscle of the bovine host following schizogony. The fine structure of the immature cyst within muscle fibers of the ventricular myocardium was studied in relation to its development and to the multiplication of parasites within it. The young cyst is enclosed by a cyst wall containing numerous small protuberances. Metrocytes within the cyst are irregular in shape and are separated from each other and the cyst wall by a thin layer of ground substance. The parasite multiplies by endodyogeny within the metrocyte. As the cyst enlarges, the host muscle fiber is disrupted and large protrusions are present in the cyst wall.