Sarcocystis spp.
- Parasite
- For completeness
A coccidian parasite acquired from undercooked beef or pork (intestinal form) or from food contaminated with animal feces (muscle form).
Also called: sarcocystosis, Sarcocystis hominis, Sarcocystis suihominis
Quick facts
- Type
- Parasite · Apicomplexans
- Gram / shape
- Thin-walled oocysts with two sporocysts in stool
- Spread
- Intestinal form · Muscular form
- Causes
- Intestinal sarcocystosis · Muscular sarcocystosis
- Treatment
- The intestinal form usually needs no specific treatment
At a glance
- Shape
- Thin-walled oocysts with two sporocysts in stool; sarcocysts full of bradyzoites in muscle
- Family
- Sarcocystidae
- Type
- Intracellular coccidian protozoan (apicomplexan) with two hosts
- Stain
- Wet mount of stool (sporocysts autofluoresce under UV); histology of muscle biopsy
- Size
- Oocysts about 15 to 20 µm
Morphology
- Oocyst with a fragile wall and two sporocysts, each with four sporozoites; free sporocysts are often seen.
- Sarcocyst: an elongated cyst inside a muscle fiber, packed with banana-shaped bradyzoites.
- Close relatives of Toxoplasma and Cystoisospora.
Transmission
- Intestinal form: eating raw or undercooked beef (S. hominis) or pork (S. suihominis) with sarcocysts.
- Muscular form: swallowing sporocysts from the feces of a carnivore (for example in water or food); here the human is a dead-end intermediate host.
- Not spread from person to person.
Reservoir: Cattle and pigs (intermediate hosts of the human intestinal species); Wild carnivores and their prey for the species that cause muscle disease
Isolation precautions
What the care team adds to standard precautions.
- Standard
Life cycle
- Cattle or pigs swallow sporocysts shed in human stool.
- Sporozoites multiply in blood vessel endothelium (schizogony) for two generations.
- Merozoites enter muscle fibers and form sarcocysts full of bradyzoites.
- A person eats undercooked meat with sarcocysts.
- Bradyzoites invade the intestinal wall and form gametes; fertilization gives oocysts.
- Oocysts sporulate in the gut wall and are passed in stool, often as free sporocysts.
Virulence factors
- Intestinal form: mild damage to the intestinal lining.
- Muscular form: cysts in muscle and heart fibers with inflammation (eosinophilic myositis, vasculitis).
Diseases it causes
- Intestinal sarcocystosis: often silent or mild and self-limited; nausea, abdominal pain and diarrhea a few hours after eating raw meat. Acute (viral) gastroenteritis →
- Muscular sarcocystosis: fever, myalgia, weakness and transient swelling, with eosinophilia and raised creatine kinase; outbreaks have occurred in travelers to Southeast Asia.
Clinical picture
- Suspect the muscular form in a returning traveler with fever, myalgia, eosinophilia and high CK without another cause.
- Its main differential diagnosis is trichinellosis.
Diagnosis
- Intestinal: oocysts or sporocysts in stool; they are shed in small numbers and are easy to miss; species cannot be told apart by morphology.
- Muscular: sarcocysts on muscle biopsy; eosinophilic myositis supports but does not confirm it.
- Molecular and serologic tests are not widely available.
Treatment
The intestinal form usually needs no specific treatment. For the muscular form there is no proven therapy; albendazole has been reported in a case and corticosteroids may relieve symptoms.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Cooking beef and pork thoroughly; freezing reduces risk.
- Safe drinking water and washing raw vegetables in endemic areas.
- Keeping human feces away from cattle and pig pastures.
Test yourself
Think of the answer, then tap the question to see it.
How does a person get intestinal sarcocystosis?
By eating raw or undercooked beef (S. hominis) or pork (S. suihominis) that contains sarcocysts.
What is the human's role in muscular sarcocystosis?
A dead-end intermediate host: sporocysts from carnivore feces reach the muscles and form cysts.
Which findings suggest muscular sarcocystosis in a traveler?
Fever, myalgia and weakness with eosinophilia and raised creatine kinase, with no other explanation.
How is the muscular form confirmed?
By finding sarcocysts in a muscle biopsy.
Connections
← Back to the group: Apicomplexans
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: CDC - DPDx - Sarcocystosis (CDC, 2024); Clinical Care of Sarcocystosis | Sarcocystosis | CDC (CDC, 2024).
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Representative model, for educational purposes only.