Causal Agent:

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:

Sarcocystis hominis lifecycle

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.

Life cycle image and information courtesy of DPDx.

Page last reviewed: August 29, 2012