Enteric Helminths (Nematodes, Trematodes, Cestodes, Acanthocephalans) and Balantioides – 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 routine microscopy testing information for enteric helminth and Balantioides (syn. Balantidium) infections at Public Health Ontario (PHO).

The parasitic helminths detectable by microscopy in enteric specimens include:

Enteric Helminths	Organisms
Nematodes (roundworms)	Trichuris, Paracapillaria (syn. Capillaria), Trichostrongylus, Oesophagostomum, Ternidens, Mammomonogamus, Ascaris, Ancylostoma, Necator, Strongyloides
Trematodes (flukes)	Schistosoma, Opisthorchiidae (incl. Clonorchis and Opisthorchis), Fasciola, Dicrocoelium, Eurytrema, Echinostomatidae, Heterophyidae, Nanophyetidae, Gymnophallidae, Brachylaimidae, Diplostomatidae, Fasciolopsis, Paramphistomatidae, Lecithodendriidae, Plagiorchiidae, Paragonimus
Cestodes (tapeworms)	Diphyllobothriidae (incl. Dibothriocephalus, Dipyllobothrium, Adenocephalus), Taenia, Rodentolepis, Hymenolepis, Dipylidium, Bertiella, Raillietina, Inermicapsifer, Mesocestoides
Acanthocephalans (thorny-headed worms)	Moniliformis, Macracanthorhynchus, Bolbosoma, Corynosoma, Acanthocephalus, Pseudoacanthocephalus

Updates
This page is for enteric specimen microscopy testing only. Additional testing options exist for some enteric organisms, refer to the following webpages for information:

*Uncontrolled print copy. Valid only on day of print: 17 Dec 2025.

Testing Indications

Microscopy may be indicated for the diagnosis of individuals suspected of a helminthic or Balantioides infection or based on compatible clinical and epidemiological evidence. In some instances, other testing methods such as PCR and/or serology may be more appropriate (see background listing above for details).

Note: Fecal microscopy is inadequate for detecting Enterobius vermicularis (pinworm). If pinworm infection is suspected, testing specimen collected from the perianal skin folds (e.g. pinworm paddle) is preferred. For detection and testing of pinworm paddle – refer to this PHO webpage: Enterobius (Pinworm) – Microscopy.

Acceptance/Rejection Criteria

Accepted Submissions:
Enteric helminth microscopy will only be accepted in cases with any of the following documented on the requisition:

International travel/migration (except continental United States and Western Europe)
Livestock exposure (e.g., farmer)
Undercooked seafood, amphibian, reptile, or gastropod ingestion
Impaired immune system (e.g., HIV, transplant, steroids)
Unexplained eosinophilia
Known positive serological test for a parasitic infection (specify which organism)
Close contact of an infected person (e.g., household member or outbreak cluster)

Rejected or Cancelled Submissions:

Enteric specimens received in vials without sodium acetate, acetic acid, and formalin (SAF) are ineligible.
Specimens submitted from animal (e.g. pets) or environmental (e.g. food) sources .

Note: Only one specimen per patient per collection date will be tested. Any additional specimens collected on the same date will not be tested. If submitting multiple specimens, ensure each is collected at least 1 to 2 days apart for them to be eligible for testing.

Specimen Collection and Handling

Specimen Requirements

Test Requested

Required Requisition(s)

Specimen Type

Minimum Volume

Collection Kit

Helminth-Microscopy

Nematode-Microscopy

Trematode-Microscopy

or Fluke-Microscopy

or Cestode-Microscopy

or Acanthocephalan-Microscopy

or Worm-Microscopy

or Balantioides – Microscopy

General Test Requisition

Enteric specimens (e.g., stool, intestinal biopsy / aspirate / scraping, Entero-Test)

1.0 ml

SAF vial

Submission and Collection Notes

Complete all fields of the requisition form.

Important: Specify which organism(s) are suspected on the requisition, if known.

Important: Specify any of the following testing indications on the requisition. Failure to provide this information may result in rejection:

International travel/migration (except United States and Western Europe)
Livestock exposure (e.g., farmer)
Undercooked seafood, amphibian, reptile, or gastropod ingestion
Impaired immune system (e.g., HIV, transplant, steroids)
Unexplained eosinophilia
Known positive serological test for a parasitic infection (specify which organism)
Close contact of an infected person (e.g. household member or outbreak cluster)

Important: Make sure that the enteric 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. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay.

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

Limitations

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.

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

Stat and Critical Specimens Testing

For Strongyloides priority testing, refer to the following PHO webpage: Strongyloides (Strongyloidiasis – Microscopy and Antibody.

Test Methods

Microscopy is performed at PHO using diphasic sedimentation by formalin and ethyl acetate (FEA).

Performance and Limitations:
In general, microscopy sensitivity of a single enteric specimen ranges from 15-70% depending on the organism type, intensity of infection, time from exposure (i.e. prepatent period), and intermittent shedding patterns. Therefore, a single negative microscopy result does not rule out infection. Multiple (e.g., 2 or 3) specimens may be collected to increase sensitivity. Inadequate specimen volume or delayed mixing of the specimen and SAF fluid in the vial may lead to poor preservation of organism morphology and uninterpretable results. Some organisms are only identifiable in enteric specimens at the genus or family level.^1-11

Interpretation

Microscopy:

Helminth Microscopy	Interpretation
Helminth(s) found	The organism name(s) and stage(s) will be reported.
No helminths found	No evidence of parasitic organism(s). Does not rule out infection. This assay does not test for apicomplexans or microsporidia. In some instances, other testing methods such as PCR and/or serology may be more appropriate, refer to our website for testing instructions.

Note for Fasciola and Dicrocoelium/Eurytrema:if the patient recently ingested liver products, clinical correlation and repeat testing several days after a liver-free diet may be advised to rule out spurious passage.

Note for Taenia solium: assessment of the patient and their close contacts (e.g. household members) is recommended for potential cysticercosis co-infection.

Note for Strongyloides: Prompt assessment and treatment is advised. If not already requested, screening for HTLV-1 coinfection may be advised to assess the risk of hyperinfection following CATMAT guidelines.¹²

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

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