Enteric Apicomplexans (e.g. Cystoisospora, Sarcocystis) – Microscopy

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Background
This page provides microscopy testing information for enteric apicomplexans including cystoisosporiasis and sarcocystosis at Public Health Ontario (PHO).

The causative agent of cystoisosporiasis is the parasitic apicomplexan Cystoisospora (syn. Isospora) belli. Clinical manifestations include persistent malabsorptive enteritis following travel to or residence in subtropical or tropical regions. While severe or chronic disease is more commonly observed in individuals with impaired immunity, cases have also been reported in immunocompetent individuals.^1-2

The causative agents of intestinal sarcocystosis are the parasitic apicomplexan Sarcocystis hominis and S. suihominis. Clinical manifestations include acute enteritis following consumption of undercooked meat exposure. The causative agents of muscular sarcocystosis are zoonotic species of Sarcocystis such as S. nesbitti. Clinical manifestations include subacute or relapsing febrile myositis following exposure to untreated water sources in endemic regions (e.g. rural Southeast Asia).

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

* Copie d'impression non contrôlée. Valide uniquement le jour de l'impression : 19 oct. 2026.

Testing Indications

Microscopy is recommended for the diagnosis of individuals with clinical and epidemiological evidence suggestive of cystoisosporiasis or sacrocystosis. For muscular sacrocystosis specifically, histopathological examination of formalin-fixed paraffin-embedded (FFPE) muscle tissue is preferred over of fresh tissue microscopy.

Note: Currently, PCR and serological (antibody) testing for Cytoisospora and Sarcocystis are not available at PHO.

Acceptance/Rejection Criteria

To ensure appropriate testing and accurate results, the following criteria must be met. Specimens that do not meet these requirements will be rejected.

Accepted if the requisition includes one of the following:

Signs or symptoms consistent with infection
International travel/migration (except continental United States and Western Europe)
Undercooked meat ingestion
Impaired immune system (e.g., HIV, transplant, steroids)
Unexplained eosinophilia
Close contact of an infected person (e.g., household member or outbreak cluster)

Rejected if:

Specimens are from non-human sources such as animals (e.g. pets) or environmental (e.g. food or water).

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Enteric Apicomplexan – Microscopy	General Test Requisition	Enteric specimens (e.g., feces, intestinal biopsy / aspirate / scraping, Entero-Test)	1.0 ml	SAF vial
Sarcocystis – Microscopy	General Test Requisition	Tissue specimens (e.g. muscle biopsy)	0.2 ml	Sterile empty 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.

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.

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. 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 and Peterborough sites. Turnaround time is up to 7 calendar days from receipt at PHO.

Microscopy on other specimens (non-enteric) 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:
Microscopy sensitivity for detection of Cystoisospora is unknown and likely low. Infections are often persistent and may intermittently shed in feces, therefore multiple (e.g., 2 or 3) specimens may be collected to increase sensitivity. ^1,2

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. Microscopy at PHO cannot distinguish between species of the Sarcocystis genus.^3,4

For muscular sarcocystosis, microscopy sensitivity is unknown and likely low, with one small study observing a 75% (3/4) sensitivity in biopsied muscles. ⁵

Interpretation

Microscopy:

Apicomplexan Microscopy	Interpretation
Apicomplexan(s) found	The organism name(s) and stage(s) will be reported.
No apicomplexans found	No evidence of apicomplexan organisms. Due to the limited test sensitivity, testing of additional specimens may be considered if clinically indicated. This assay does not test for helminths, microsporidia, or other protozoa.

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

Dubey JP, Almeria S. Cystoisospora belli infections in humans: the past 100 years. Parasitology. 2019 Oct;146(12):1490-1527. doi: 10.1017/S0031182019000957. Epub 2019 Aug 9. PMID: 31303182.
Lindsay DS, Dubey JP, Blagburn BL. Biology of Isospora spp. from humans, nonhuman primates, and domestic animals. Clin Microbiol Rev. 1997 Jan;10(1):19-34. doi: 10.1128/CMR.10.1.19. PMID: 8993857; PMCID: PMC172913.
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.