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Sarcocystis spp. (Pathogen)

Organism:
This organism belongs to the coccidia.  The organism once known as Isospora hominis is now recognized as being a part of the life cycle of Sarcocystis spp. Two well‑described species are Sarcocystis bovihominis (cattle) and S. suihominis (pigs). When uncooked meat from these infected animals is ingested by humans, gamogony can occur within the intestinal cells, with the eventual production of the sporocysts in stool. Some publications refer to S. bovihominis as S. hominis. In this case, humans who have ingested meat containing the mature sarcocysts serve as the definitive hosts

sarco1 sarco2 sarco3
Sarcocysts in muscle
Sporocysts; oocyst wall appears to be missing

Life Cycle:
Intestine,     Species of Sarcocystis have an obligatory 2-host life cycle.  Intermediate hosts such as herbivores and omnivores become infected through ingestion of sporocysts excreted in the feces of the definitive host such as carnivores and omnivores.  The definitive hosts become infected through ingestion of mature cysts found in muscles of the intermediate hosts.  In some intermediate hosts, such as cattle and sheep, all adult animals may be infected. 

Acquired:
Fecal-oral transmission via oocyst form; contaminated poorly cooked meat

Epidemiology:
Worldwide, human-to-human transmission, food-borne and waterborne transmission

Clinical Features:
Muscle: When humans accidentally ingest oocysts from other animal stool sources, the sarcocysts that develop in human muscle apparently do little if any harm (schizogony). The prepatent period in humans is from 9 to 10 days.  There is essentially no inflammatory response to these stages in the muscle and no conclusive evidence of pathogenicity of the mature sarcocyst. However, symptoms have been seen in some patients, probably associated with disintegration of the sarcocysts. Painful muscle swellings, measuring 1 to 3 cm in diameter, initially associated with erythema of the overlying skin in various parts of the body, occur periodically and last for 2 days to 2 weeks. Some patients also have fever, diffuse myalgia, muscle tenderness, weakness, eosinophilia, and bronchospasm.
Intestine: When humans serve as definitive hosts, prevention involves adequate cooking of beef and pork; when humans are intermediate hosts, preventive measures involve careful disposal of animal feces that may contain the infective sporocysts. This may be impossible in the wilderness areas, where wild animals may serve as reservoir hosts for many of the different types of organisms that have been grouped under the term Sarcocystis "lindemanni." However, this name is no longer used. 

Clinical Specimen:
Muscle:  Biopsy.  Intact sarcocysts in skeletal or cardiac muscle of humans measure up to 100 by 325 μm and are usually not accompanied by an inflammatory reaction. Each sarcocyst contains many bradyzoites, approximately 7 to 16 μm long. Inflammation follows disintegration of the cysts and death of the intracystic bradyzoites. Vasculitis is seen in the muscle and subcutaneous tissues. Histologic findings include myositis with vasculitis and sometimes myonecrosis.
Intestinal:  Stool. 

Laboratory Diagnosis:
Muscle:  Routine histology
Stool:  Ova and Parasite examination (concentration most important method)

Organism Description:
Sarcocyst:  Sarcocysts measure up to 100 by 325 µm; each sarcocysts contains many bradyzoites, approximately 7 to 16 µm long.
Oocyst:  Oocysts measure 15-19 by 8-10 µm; oocyst wall appears to be missing; can’t differentiate S. hominis from S. suihominis.

Laboratory Report:
Sarcocystis oocysts or sarcocysts from tissue

Treatment: 
Garcia, L.S. 2007.  Diagnostic Medical Parasitology, 5th ed., ASM Press, Washington, D.C.
No specific therapy is known for the muscle stages; however, corticosteroids should reduce the allergic inflammatory reactions occurring after cyst rupture.

Control:
Improved hygiene, adequate disposal of fecal waste, adequate washing of contaminated fruits and vegetables