Sarcocystis (Sarcocystosis) – Microscopy

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides microscopy testing information for intestinal or muscular sarcocystosis at Public Health Ontario (PHO). The causative agents of intestinal sarcocystosis are the parasitic apicomplexan Sarcocystis hominis and S. suihominis. The causative agents of muscular sarcocystosis are zoonotic species of Sarcocystis such as S. nesbitti.

For information on other protozoan testing options—excluding Sarcocystis—please refer to the following test information sheet: Enteric Protozoa (Cryptosporidium, Cyclospora, Dientamoeba, Entamoeba, and Giardia) - PCR.

Updates
This webpage has been updated to include background information, testing indications, acceptance criteria, performance characteristics and limitations, result interpretations, and expected turnaround times based on calendar days instead of business days for both intestinal and muscular infections.

*Uncontrolled print copy. Valid only on day of print: 18 Dec 2025.

Testing Indications

Intestinal sarcocystosis: Microscopy on enteric specimens may be considered for individuals presenting with clinical and epidemiologic features consistent with intestinal sarcocystosis -such as acute enteritis following consumption of undercooked meat exposure.

Muscular sarcocystosis: Microscopy of fresh muscle tissue specimens may be considered for individuals exhibiting compatible clinical and epidemiologic evidence of muscular sarcocystosis such as subacute or relapsing febrile myositis following exposure to untreated water sources in endemic regions (e.g. rural Southeast Asia). However, histopathological examination of formalin-fixed paraffin-embedded (FFPE) muscle tissue is preferred over of fresh tissue microscopy.

Note: Currently, PCR or serological testing for Sarcocystis are not available at PHO.

Acceptance/Rejection Criteria

To ensure timely and accurate testing, review the following criteria before submitting specimens:

Clinical and Exposure Information Required
Specimens submitted without relevant clinical or exposure information may be rejected or experience delays in testing.
Proper Specimen Preservation Required
Enteric specimens received without sodium acetate, acetic acid, and formalin (SAF) preservation are ineligible and will be cancelled.
Specimen Collection Timing
If submitting more than one specimen, ensure that each specimen is collected at least 1 to 2 days apart. If multiple specimens collected on the same date are received, only one specimen will be tested.
Human Specimens Only
Only human-derived specimens are accepted. Specimens from animals (e.g. pets) or environmental sources (e.g. food, water) will be rejected.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Sacocystis or Apicomplexan - Microscopy	General Test Requisition	Enteric specimens (e.g., feces, intestinal biopsy / aspirate / scraping, Entero-Test)	1.0 ml	SAF vial
Sacocystis or Apicomplexan - Microscopy	General Test Requisition	Other specimens (e.g. muscle biopsy / aspirate)	N/A	Empty sterile vial

Submission and Collection Notes

Complete all fields of the requisition form.

If submitting SAF-preserved enteric specimens for microscopy: make sure that the specimen and SAF fluid is mixed thoroughly as soon as collection occurs to preserve the specimen fully.

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

If the patient is part of a cluster/outbreak investigation, contact PHO Laboratory Customer Service at 416-235-6556/1-877-604-4567 prior to sample submission.

Timing of Specimen Collection

Intestinal sarcocystosis: Microscopy may be negative within the first 2 weeks post-exposure (i.e. prepatent period), including during the acute diarrheal phase. If the clinical suspicion is high, enteric specimens should be collected both during acute illness and 1 to 2 weeks after symptom onset due to this paradoxically delayed shedding of Sarcocystis in feces.

Limitations

For enteric specimens: Avoid antacids or antimicrobials at least 2-3 weeks before collection as it can alter the intestinal microbiome. Avoid laxatives/enemas (e.g. mineral/castor oil), nonabsorbable antidiarrheal preparations (e.g. bismuth), and kaolin at least 7-10 days before collection as it can affect the staining process. Avoid contrast dyes (e.g. barium) at least 3 weeks before collection as it can affect the staining process. Avoid contact between feces and urine or water during collection.

Storage and Transport

Place specimen container in a biohazard bag and properly seal the bag.

SAF specimens can be stored at room temperature (or alternatively 2-8°C) and shipped to PHO within 48 hours of collection. Other unpreserved specimens should be stored at 2-8°C and shipped to PHO within 48 hours of collection. All specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Microscopy on enteric specimens is performed daily from Monday to Friday at PHO’s laboratory- Toronto, Peterborough, Ottawa, and London sites. Turnaround time is up to 7 calendar days from receipt at PHO.

Microscopy on other specimens is performed daily from Monday to Friday at PHO’s laboratory -Toronto site only. Turnaround time is up to 7 calendar days from receipt at PHO.

Test Methods

Microscopy is performed at PHO using acid-fast staining technique.

Performance and Limitations:
For intestinal sarcocystosis, microscopy sensitivity during the prepatent acute diarrheal phase is usually low (< 30%). Multiple (e.g., 2 or 3) specimens collected 1 to 2 weeks after exposure or symptom onset is usually recommended to increase sensitivity. Inadequate specimen volume or delayed mixing of the enteric specimen and SAF fluid in the vial may lead to poor preservation of organism morphology and uninterpretable results. Microscopy at PHO cannot distinguish between species of the Sarcocystis genus.^1,2

For muscular sarcocystosis, microscopy sensitivity is unknown and likely low, with one small study observing a 75% (3/4) sensitivity in biopsied muscles. ³

Interpretation

Apicomplexan Microscopy	Interpretation
Apicomplexan(s) found: Sarcocystis species	The organism stage(s) will be reported. Species level identification cannot be made by microscopy.
No apicomplexans found	No evidence of Sarcocystis organisms. Due to the limited test sensitivity, testing of additional specimens may be considered if clinically indicated.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

References

Van Den Broucke S, Dorny P, Van Esbroeck M, Bottieau E. Microscopic Detection of Intestinal Sarcocystis Infection Diagnosed in International Travelers at the Institute of Tropical Medicine, Antwerp, Belgium, from 2001 to 2020. Am J Trop Med Hyg. 2023 Jun 5;109(2):327-331. doi: 10.4269/ajtmh.22-0577. PMID: 37277109; PMCID: PMC10397430.
Poulsen CS, Stensvold CR. Current status of epidemiology and diagnosis of human sarcocystosis. J Clin Microbiol. 2014 Oct;52(10):3524-30. doi: 10.1128/JCM.00955-14. Epub 2014 Apr 23. PMID: 24759707; PMCID: PMC4187749.
Italiano CM, Wong KT, AbuBakar S, Lau YL, Ramli N, Syed Omar SF, Kahar Bador M, Tan CT. Sarcocystis nesbitti causes acute, relapsing febrile myositis with a high attack rate: description of a large outbreak of muscular sarcocystosis in Pangkor Island, Malaysia, 2012. PLoS Negl Trop Dis. 2014 May 22;8(5):e2876. doi: 10.1371/journal.pntd.0002876. PMID: 24854350; PMCID: PMC4031117.