Sarcocystis

A genus of protozoan parasites, related to the sporozoan genera Eimeria, Isospora, and Toxoplasma, and placed in a distinct family, Sarcocystidae, but with the above genera in the same suborder, Eimeriina, within the subclass Coccidia, class Sporozoea, and phylum Apicomplexa. Tissue stages of S. are usually seen as thick-walled cylindrical or (often extremely large (1 cm or more), fusiform cysts (Miescher tubes) in reptile, bird, or mammal striated muscles. Cysts are smooth in the house mouse form or with radial spines (cytophaneres) in sheep or rabbit; contents may be compartmentalized by septa. Variably shaped spores (Rainey corpuscles) probably are peripheral rounded cells (sporoblasts, cytomeres) that divide to form mature “spores” (bradyzoites), motile bodies when released from the cyst; sexual stages have been described in tissue cultures. These parasites are abundant but rarely of pathogenic significance. Humans who have ingested meat containing the mature sarcocysts serve as the definitive hosts; fever, severe diarrhea, abdominal pain, and weight loss have been reported in a small number of immunocompromised hosts. When humans accidentally ingest oocysts from other animal stool sources, the sarcocysts that develop in human muscle appear to cause no inflammatory response. [sarco- + G. kystis, bladder]

- S. bovih′ominis SYN: S. hominis.

- S. fusiformis a species found in the striated and heart muscle of cattle and water buffalo.

- S. hominis a species now recognized as a two-host infection, with beef serving as the intermediate host source of infective tissue cysts to humans, who serve as the final host. Gamogony and sporogony occur in mucosal cells of the human small intestine; cattle become infected from human feces contaminated with S. hominis sporocysts. SYN: S. bovih′ominis.

- S. lindemanni a protozoan species described on rare occasions from the striated and heart muscles of humans, probably as an infection due to various species, possibly from domestic dogs or other final hosts from which infective oocysts or sporocysts were passed to humans via water or direct exposure; in these instances humans serve as an intermediate rather than a final host.

- S. miescheriana a common species of worldwide distribution that is found in the striated and heart muscle of pigs; it is the type species of the genus S..

- S. suihominis a form of S. in which humans serve as the final host, with the pig serving as intermediate host, the source of infected tissues to humans. The life cycle and moderate disease induced follow the pattern of S. hominis, though the disease appears to be somewhat more pathogenic. Human infection is widespread, having been reported in Europe, the Mediterranean, West Africa, Indonesia, and South America.

- S. tenella an extremely common species of worldwide distribution that is found in the striated and heart muscle of sheep and goats.

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sar·co·cys·tis .sär-kə-'sis-təs n

1) cap a genus of sporozoan protozoans of the order Sarcosporidia that form cysts in vertebrate muscle

2) pl -tis or -tis·es any sporozoan protozoan of the genus Sarcocystis broadly any of the order Sarcosporidia

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n.

a genus of parasitic protozoans (see Sporozoa) that infect birds, reptiles, and herbivorous mammals. S. lindemanni, which occasionally infects humans, forms cylindrical cysts (sarcocysts) in the muscle fibres. In heavy infections these cysts can cause tissue degeneration and therefore provoke muscular pain and weakness. Sarcocysts have, in the few positively diagnosed cases, been located in the heart muscles, arm muscles, and larynx.

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Sar·co·cys·tis (sahr″ko-sisґtis) [sarco- + Gr. kystis bladder] a genus of coccidian protozoa (suborder Eimeriina, order Eucoccidiida) that are parasitic in birds, reptiles, and mammals and occur as elongated cylindrical bodies called sarcocysts in the host's muscles. They have an obligatory two-host life cycle, with sexual reproduction in the definitive host (a carnivore) and asexual reproduction, including schizogony and sarcocyst formation. Infection of the definitive host is usually the result of eating meat of an infected animal; infection of the intermediate host occurs when these animals accidentally ingest sarcocysts from feces contaminating their food supply. See also sarcocystosis.