Scanning and transmission electron microscopy of ovine mesenteric arteries infected with first-generation meronts of Sarcocystis tenella

Abstract

First-generation meronts of Sarcocystis tenella were found within subendothelial cells between the endothelium and internal elastic membrane of mesenteric arteries. At 14 and 16 days postinoculation (DPI), host cells with mature meronts were enlarged, measuring 25.6 × 22 μm (16.4–35 × 4.4–28.5 μm; n = 17), which caused the endothelium to protrude into the vessel lumen. In mesenteric arteries, protuberances measured 37.4 × 29.7 μm (32–57 × 16.5–47 μm; n = 15) and extended 16.8 μm (12–27 μm; n = 12) into the vessel lumen. Merozoites in meronts measured 5.3 × 1.7 μm (4.5–5.5 × 1.5–1.8 μm; n = 20); free merozoites were 5.5 × 1.5 μm (4.8–6 × 1.3–1.7 μm; n = 18). At 16 DPI many of the endothelial cells covering protuberances as well as many of the host cells had sloughed from the tunica intima of the mesenteric arteries which exposed relatively large areas, 189.5 μm (50–350 μm; n = 15) in diameter, of the internal elastic membrane.