Electron microscopic studies on the development of Sarcocystis capracanis in experimentally infected goats.

On the 12th, 20th and 21st day after infecting goats orally with sporocysts of S. capracanis from the faeces of dogs which had been infected with raw meat containing Sarcocystis of naturally infected goats, mature schizonts were found in the cytoplasma of endothelial cells of the veins in the liver, spleen, kidney and brain. The nucleus of the young schizont increases markedly in size, forming several protrusions which tore away simultaneously giving rise to numerous merozoites. The schizonts were about 30 microns in size and retained their three-layered pellicle till the merozoites matured. After rupture the schizonts set the 6 microns long daughter cells free, which were distributed by means of the blood. Though degenerated schizonts were present in the brain, the cells around the parasitized cells showed no reaction. In muscles as well as in the brain the second phase of the asexual reproduction (cyst formation) took place. The merozoites first became spherical in parasitophorous vacuoles in parasitized cells. The unit membrane of the parasitophorous vacuole which formed the primary cyst wall developed protrusions which were mostly straight, giving the aspect of a thick, striated cyst wall. A secondary cyst wall was never formed according to light microscopical studies. In a single animal thin-walled cysts occurred, which probably belonged to a second Sarcocystis species. The protrusions of both cyst-types contained no filaments. Cyst maturation took about 1 month, so that on the 65th day p.i. numerous infectious, banana-shaped merozoites (15 microns long) were still present as well as some metrocytes (12 microns long) which were constantly reproducing by endodyogeny.