Sarcocystis hominis, one of the three species of Sarcocystis that cause muscular cysts in cattle, is a protozoan parasite that can infect the human intestinal tract. S. hominis infection in humans is characterized by transient nonspecific gastrointestinal complaints consist of nausea, stomachache and diarrhea. The clinical course usually is mild and in many cases asymptomatic, although the severity is correlated with the number of ingested sarcocysts. There is high infection rate of sarcocyst in cattle in Iran but to our knowledge, no study about Sarcocystis species identification. This work aimed to survey existence of S. hominis. In this study, esophagus and diaphragm muscles of 100 cattle were collected from Fesaran abattoir of Isfahan and examined for the presence of Sarcocystis spp macroscopically and by means of light and electron microscope. For histopatological examination, tissue samples were taken from the esophagus and diaphragm muscles and fixed in 10% neutral buffered formalin. They were processed and embedded in paraffin. Sections of 5 μm thickness were cut and stained with haematoxylin and eosin. Some formalin-fixed tissues and cysts were postfixed in osmium tetraoxide solution, after that the specimens were processed for transmission electron microscopic observation. Macroscopic examination of the muscles from cattle show no gross sarcocysts. Histopathological examinations revealed thin and thick walled cysts. S. hominis cysts were observed in 10% of the examined cattle. The cysts had thick, radially striated walls, and were 30-137.5 × 20-70 μm in size and their wall was 3 to 6 μm thick. S. hominis cyst walls appeared radially striated in the histopathological sections because of the presence of palisade-like villar protrusions. Ultrastructural features of the protrusions by TEM, were broad-based, blunt distal end cylindrical, contained microtubules, and oriented nearly perpendicularly to the sarcocyst surface. Based on histopathological and ultrastructural features of the cysts, we identified them as S. hominis. Due to presence of this Sarcocystis species in our region, it should be avoided from eaten undercooked and raw beef to prevent human sarcocystosis.

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