Fine structure of Sarcocystis singaporensis merogony stages preceding sarcocyst formation in the rat.

The fine structure of merogony stages of Sarcocystis singaporensis (Zaman and Colley, 1975) is described from experimentally infected laboratory rats, 10 days after being fed sporocysts obtained from naturally infected Python reticulatus from Singapore. Infection was shown to consist exclusively of S. singaporensis. Parasites developed in the endothelial cells of the lungs, brain, kidney and heart. Infection comprised meronts prior to division, dividing and divided meronts, and dispersed merozoites. Undivided meronts developed deep pellicular invaginations and extensions of the nucleus toward the cell boundary, seemingly to sustain metabolic exchange. The course of merogonous development was the same in all organs. Hypertrophy of the endothelium induced by invading merozoites appeared to lead to obstruction of the capillary lumen.