Electron Microscopy of Sarcocystis fusiformis

Abstract

Thin sections of cysts of Sarcocystis fusiformis were studied in situ in the myocardium. Cysts were enclosed by a cyst wall. The external boundary of the cyst wall consisted of alternating long and short villous-like projections. Some long villi were seen within vacuoles in the surrounding myocardial cells. The basal portion of the cyst layer contained interwoven fibrils. The cells of S. fusiformis contained three regions. The anterior third contained sarconemes which seemed to originate in the conoid. The middle zone contained mitochondria and many bodies of various sizes, shapes, and electron density. The posterior portion of the cell contained a prominent nucleus, osmophilic bodies, and mitochondria. Spindle-shaped cysts are frequently seen in histologic sections of the myocardium of normal cattle. These cysts are referred to as Miescher's tubules and are readily discernible by low magnification light microscopy. Rounded cells in cysts have been designated as trophoblasts and banana-shaped cells as trophozoites (Levine, 1961). However, the fine cellular detail of sarcosporidial cells within cysts is not revealed by light microscopy, even though the presence of a nucleus has been resolved by the Feulgen reaction (Breindl and Komarck, 1928). Recently the electron microscope has been used to determine the fine structure of Sarcocystis tenella (see Ludvik, 1958; Senaud and de Puytorac, 1961, 1962) and S. miescheriana (see Ludvik, 1960), the agents of sarcosporidiosis in sheep and pigs, respectively. The ultrastructural morphology of Sarcocystis of bovine origin, S. fusiformis (species presumed on the basis of host in which it was found), is described in this paper. Previous publications of the ultrastructure of Sarcocystis have used fresh material obtained from the musculature of infected animals whereas in this study the cysts of Sarcocystis were examined in infected musculature in situ. MATERIALS AND METHODS Small pieces of myocardium from the left ventricle were obtained from beef animals at a local packinghouse. The tissues were fixed in 4% glutaraldehyde in pH 7.3 Sorenson's buffer (Sabatini et al., 1963). Each sample of myocardial tissue Received for publication 20 December 1965. * This study was supported in part by a grant (H-6580) from the NIH, U. S. Public Health Service. t Florida Agricultural Experiment Stations Journal Series 2273. was cut into two sections. One portion was embedded in paraffin, cut at 5 ,u, stained with hematoxylin-eosin, and examined for Sarcocystis with the light microscope. When parasites were found in histologic sections, the corresponding area of the second portion of myocardium was prepared for electron microscopy. Glutaraldehyde-fixed musculature was washed in Sorenson's buffer, postfixed in 1%o OsO (Caulfield, 1957), and embedded in Araldite (Luft, 1961). Thin sections on grids, following staining with lead, uranyl acetate, or a combination of the two metals, were examined with a Philips EM200 electron microscope.