Clonorchis (Clonorchiasis) – Microscopy and Antibody

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 and antibody (serology) testing information for clonorchiasis at Public Health Ontario (PHO). The causative agent of clonorchiasis is the parasitic biliary trematode (“fluke”) Clonorchis sinensis.

For identification of extracted worms or worm segments, refer to the following PHO webpage: Worm (Whole or Segment) – Identification

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

Testing Indications

Microscopy is the recommended diagnostic method for individuals presenting with clinical and epidemiological features consistent of clonorchiasis, such as biliary or ectopic manifestations following ingestion of undercooked freshwater fish from endemic regions in Asia.

Serological testing is not routinely available and may only be performed with prior approval from a PHO microbiologist.

Note: Antigen detection and PCR-based testing for Clonorchis are currently not available at PHO.

Acceptance/Rejection Criteria

Accepted Submissions:

To ensure appropriate testing and avoid specimen rejection, please review the following requirements:

Microscopy for Clonorchis:
Microscopy will only be performed when both of the following criteria are documented on the requisition form:

Travel or migration history from an Asian region
Clinical signs or symptoms consistent with clonorchiasis, such as biliary or ectopic manifestations

Serology for Clonorchis:
Serological testing is not routinely available and will only be accepted upon prior approval by a PHO microbiologist. If serology is required, contact PHO Laboratory Customer Service at 416-235-6556 or 1-877-604-4567 prior to sample submission.

Notes:

Enteric specimens received without sodium acetate, acetic acid, and formalin (SAF) preservation will be deemed ineligible and cancelled.
If multiple enteric specimens are submitted with the same collection date, only one will be tested. All additional specimens collected on that same date will not be tested. To be eligible for testing, each specimen must be collected at least 1 to 2 days apart.
Specimens are only accepted if originating from human sources. Specimens submitted from animal sources (e.g. pets) or environmental sources (e.g. food) will be rejected.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Clonorchis - Microscopy	General Test Requisition	Enteric specimens (e.g., stool, intestinal biopsy / aspirate / scraping, gallbladder stones)	1.0 ml	SAF vial
Clonorchis - Microscopy	General Test Requisition	Other body fluid or tissue specimens (e.g. aspirates, biopsies)	1.0 ml (fluids)	SAF or empty sterile vial
Clonorchis - Antibody	General Test Requisition	Blood or serum	5.0 ml whole blood or 1.0 ml serum	Blood, clotted – vacutainer tubes (SST)

Submission and Collection Notes

Complete all fields of the requisition form.

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

Travel/migration from an Asian region
Signs or symptoms compatible with clonorchiasis

Important: Mix the enteric specimen thoroughly with SAF preservative immediately after collection to ensure proper preservation.

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.

Timing of Specimen Collection

For enteric specimens, microscopy may yield false-negative results during the first 2 weeks post-exposure due to the prepatent period, when Clonorchis eggs have not yet begun to appear in stool.

Limitations

For serology: Grossly haemolysed, lipemic, contaminated specimens, and specimens containing anti-coagulant are unsuitable for testing.

Storage and Transport

Place specimen container in a biohazard bag and properly seal the bag. Centrifuge tube if using Serum-Separator Tube (SST) for serum specimens.

SAF specimens can be stored at room temperature (or alternatively 2-8°C) and shipped to PHO within 48 hours of collection. Unpreserved and serum specimens should be stored at 2-8°C and shipped to PHO on ice packs 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 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.

If approved, serology is forwarded to the commercial Kephera Diagnostics laboratory in Massachusetts, United States. Turnaround time is up to 42 calendar days from receipt at PHO.

Test Methods

Microscopy on enteric specimens is performed at PHO using diphasic sedimentation by formalin and ethyl acetate (FEA). Microscopy on other specimens is performed using standard sedimentation.

Serology is performed at Kephera Diagnostics using a laboratory-developed enzyme-linked immunoassay (ELISA) based on antibody capture using proprietary recombinant antigens.

Performance and Limitations:
Microscopy sensitivity of a single enteric specimen ranges from 15-70% depending on the 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 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 Opisthorchiidae family (including Clonorchis, Opisthorchis, Metorchis, Amphimerus); submission of the adult worm is needed to provide further genus or species level identification.^1-6

For serology, Kephera Diagnostics reports a sensitivity of 97% and a specificity of 96% based on the manufacturer’s data. In other similar assays, reported sensitivity is around 80% and specificity ranges from 70 to 90%, with decreased sensitivity observed in mild infections or in elderly populations and potential cross-reactivity with other helminth infections (e.g. other trematodes).^7-11

Interpretation

Microscopy:

Helminth Microscopy	Interpretation
Helminth(s) found: *Opisthorchiidae* family	The organism stage(s) will be reported. May include Clonorchis, Opisthorchis, Metorchis, and Amphimerus. Genus/species level identification cannot be made via the ova stage but only via the adult worms. Assessment of close contacts sharing a similar diet (e.g. household members) is recommended.
No parasites found	No evidence of Opisthorchiidae ova. Due to the limited test sensitivity, testing of additional specimens may be considered if clinically indicated.

Serology:

ELISA Result	Interpretation
Positive	Clonorchis antibodies detected. Does not distinguish current from resolved or past infection. Cross-reactivity may occur with other infections. Assessment of close contacts sharing a similar diet (e.g. household members) is recommended.
Negative	Clonorchis antibodies NOT detected.

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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