[Light and electron microscopic studies to the development of muscle cysts of Sarcocystis suicanis in experimentally infected pigs (author's transl)].

Six young pigs were experimentally infected with 100000 sporocysts of Sarcocystis suicanis and killed on the 32nd, 47th, 55th, 64th, 81th and 90th day p.i. The ultrastructure of sarcocysts in the muscle cells was studied. Light microscopical preliminary examination on the 32nd day p.i. showed cysts which lay in muscle fibres and were surrounded by a fine membran. On the 55th day p.i. the cyst wall showed radial light and dark stripes of 2.6 micrometer thickness, which reached a thickness of 3.2 micrometer on the 90th day p.i. The electron microscopic study of the cyst wall on the 32nd day p.i. showed a unit membran the numerous small outward projections of which are underlined by osmiophilic material that is absent in the inwardly directed invaginations. During the growth of the cyst, this primary cyst wall became regularly folded, forming many protrusions on the 55th day p.i. These appeared palisade-like and contained 57--62 filamentous elements in a single layer under the primary wall at a distance of 10 nm. In the centre of the protrusions there were 5--8 groups, comprising 2--5 filaments each. They have their origin in the ground-substance. As these filaments maintain their arrangement also in old cysts, they can be regarded as characteristic of Sarcocystis suicanis. The groundsubstance is homogenous; on the 32nd day p.i. it contained only metrocytes, and developed septa towards the interior of the cyst on the 47th day p.i. The parasites were reproduced by endodyogeny and appeared very similar to the structure of all cyst forming coccidians. Some old cysts degenerated fattily and the host cells were destroyed. The cysts of Sarcocystis suicanis with complete development of the protrusions of the primary wall can thus be differentiated from cysts of Sarcocystis suihominis with certainty.