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Sarcocystosis

[Sarcocystis hominis] [Sarcocystis suihominis] [Sarcocystis spp.]

Sporulated oocysts of Sarcocystis sp. in unstained wet mounts, magnification 400x.

Sporulated oocyst of Sarcocystis sp. in unstained wet mounts, magnification 400x.


Sporulated oocysts of Sarcocystis sp. in a wet mount viewed under UV microscopy, magnification 400x.

Sporulated oocyst of Sarcocystis sp. in a wet mount viewed under UV microscopy, magnification 400x.


 Sarcocyst of Sarcocystis sp. in muscle tissue, stained with H&E (magnification 500x).

Sarcocyst of Sarcocystis sp. in muscle tissue, stained with H&E (magnification 500x).

Causal Agents

Sarcocystis hominis and S. suihominis use humans as definitive hosts and are responsible for intestinal sarcocystosis in the human host. Humans may also become dead-end hosts for non-human Sarcocystis spp. after the accidental ingestion of oocysts.


Life Cycle

Life cycle of sarcocystosis

Both sporulated oocysts (containing two sporocysts) and individual sporocysts can be passed in stool The number 1. Sporocysts contain four sporozoites and a refractile residual body. Sporocysts ingested by the intermediate host (cattle for S. hominis and pigs for S. suihominis) rupture, releasing sporozoites. Sporozoites enter endothelial cells of blood vessels and undergo schizogony, resulting in first-generation schizonts. Merozoites derived from the first-generation invade small capillaries and blood vessels, becoming second-generation schizonts. The second generation merozoites invade muscle cells and develop into sarcocysts containing bradyzoites, which are the infective stage for the definitive host The number 2. Humans become infected when they eat undercooked meat containing these sarcocysts. Bradyzoites are released from ruptured cysts in the small intestine The number 3 and invade the lamina propria of the intestinal epithelium The number 4. There, they differentiate into macro- and microgametocytes. Fusion of male and female gametes The number 5 results in the formation of oocysts The number 6. Oocysts sporulate in the intestinal epithelium and are shed from the host in feces The number 7. Due to the fragile nature of the oocyst wall, individual sporocysts may also be detected in feces.

Geographic Distribution

Worldwide, but more common in areas where livestock is raised.

Clinical Presentation

In cases of intestinal sarcocystosis, when humans serve as the definitive hosts, infections are often asymptomatic and clear spontaneously. Occasionally, mild fever, diarrhea, chills, vomiting and respiratory problems may occur. When humans become infected with sarcocysts of non-human species, the infections are not intestinal but rather result in muscle cysts; symptoms such as myalgia, muscle weakness and transitory edema may occur. In these cases, humans are dead-end intermediate hosts.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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