Paragonimus (Paragonimiasis) – 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 paragonimiasis at Public Health Ontario (PHO). The causative agent of paragonimiasis is the parasitic lung trematode (“flukes”) Paragonimus, which includes multiple species.

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

Updates
This webpage has been merged with the Paragonimus-Serology webpage and updated to include background, testing indications, acceptance criteria, performance and limitations, interpretations, and expected turnaround times, which are now expressed in calendar days instead of business days.

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

Testing Indications

Microscopy and serology are indicated for the diagnosis of individuals with compatible clinical and epidemiological evidence of paragonimiasis – such as pleuropulmonary or ectopic manifestations following ingestion of undercooked crustacean, gastropods, or wild game meat from endemic regions.

Note: Currently, antigen or PCR-based testing for Paragonimus are not available at PHO.

Acceptance/Rejection Criteria

Testing will only be accepted when both of the following are documented on the requisition:

Crustacean, gastropod, or wild game meat ingestion
Signs or symptoms compatible with paragonimiasis

Enteric specimens received without sodium acetate, acetic acid, and formalin (SAF) preservation are ineligible and will be cancelled.
If multiple enteric specimens with the same collection date are submitted, only one will be tested. If multiple specimens are collected, they should be separated at least 1 to 2 days apart for all to be eligible for testing.
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
Paragonimus - Microscopy	General Test Requisition	Enteric specimens (e.g., stool, intestinal biopsy / aspirate, gallbladder stones)	1.0 ml	SAF vial
Paragonimus - Microscopy	General Test Requisition	Other body fluid or tissue specimens (e.g. sputum, bronchoalveolar lavage, pleural fluid, aspirates, biopsies)	1.0 ml (fluids)	SAF or empty sterile vial
Paragonimus - 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:

Crustacean, gastropod, or wild game meat ingestion
Signs or symptoms compatible with paragonimiasis

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 and respiratory specimens: Microscopy may be negative within the first 2 months post-exposure due to the prepatent period, which includes the early acute migratory phase of Paragonimus infection. For sputum samples, collection immediately after waking is recommended, as overnight accumulation of lung secretions may improve the likelihood of detecting Paragonimus eggs.

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 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. Other unpreserved and serum 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 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.

Serology is forwarded to the National Reference Centre for Parasitology (NRCP) in Montreal.

Turnaround time is up to 42 calendar days from receipt at PHO.

Test Methods

Microscopy: Enteric specimens are examined at PHO using diphasic sedimentation with formalin and ethyl acetate (FEA). Microscopy on other specimens are processed using standard sedimentation techniques.

Serology: Performed at the NRCP using a laboratory-developed enzyme-linked immunoassay (ELISA) based on antibody capture using a Paragonimus antigen.

Performance and Limitations:
Microscopy is usually negative during the prepatent acute migratory pleuropulmonary phase of infection. During the chronic lung phase, sensitivity of a single respiratory specimen ranges from 10-50% depending on the intensity of infection, while sensitivity of a single enteric specimen is usually less than 15%. Therefore, a single negative microscopy result does not rule out infection. Multiple (e.g., up to 5) 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 Paragonimus genus.^1-7

For serology, the NRCP reports a sensitivity of 100% and specificity of 85% for Paragonimus infection. Elsewhere, sensitivity using other assays has been reported at above 95%. Data on performance by species is not established, and there has been reports of variable sensitivity for some species in other assays (e.g. P. kellicotti). Cross-reactivity may occur with other infections (e.g. other trematodes). Serology may be negative early in infection, and may persist for months following resolution of infection, therefore results should be interpreted with caution.^5-9

Interpretation

Microscopy:

Parasite microscopy	Interpretation
Parasite(s) found: Paragonimus species	The organism stage(s) will be reported. 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 Paragonimus ova. Due to the limited test sensitivity, testing of additional specimens may be considered if clinically indicated.

Serology (Paragonimus by EIA – Referred out):

ELISA Optical Density (OD) Value	Interpretation	Comments
> 1.50	Positive	Paragonimus antibodies detected. Does not distinguish current from resolved or past infection. Cross-reactivity may occur with other helminths. Clinical correlation required.
1.00 to 1.50	Equivocal	Inconclusive results. Repeat collection if clinically indicated.
< 1.00	Negative	Paragonimus 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

Nagayasu E, Yoshida A, Hombu A, Horii Y, Maruyama H. Paragonimiasis in Japan: a twelve-year retrospective case review (2001-2012). Intern Med. 2015;54(2):179-86. doi: 10.2169/internalmedicine.54.1733. Epub 2015 Jan 15. PMID: 25743009.
Kong L, Hua L, Liu Q, Bao C, Hu J, Xu S. One delayed diagnosis of paragonimiasis case and literature review. Respirol Case Rep. 2021 Apr 28;9(5):e00750. doi: 10.1002/rcr2.750. PMID: 33959297; PMCID: PMC8080295.
Poudyal BS, Paudel B, Bista B, Shrestha GS, Pudasaini P. Clinical, Laboratory and Radiological Features of Paragonimiasis Misdiagnosed as Pulmonary Tuberculosis. Iran J Parasitol. 2022 Jul-Sep;17(3):410-414. doi: 10.18502/ijpa.v17i3.10632. PMID: 36466025; PMCID: PMC9682384.
KOMIYA Y, YOKOGAWA M. The recovering of Paragonimus eggs from stools of paragonimiasis patients by AMS III centrifuging technic. Jpn J Med Sci Biol. 1953 Apr;6(2):207-11. doi: 10.7883/yoken1952.6.207. PMID: 13096207.
Procop GW2009.North American Paragonimiasis (Caused by Paragonimus kellicotti) in the Context of Global Paragonimiasis. Clin Microbiol Rev 22: https://doi.org/10.1128/cmr.00005-08
Hwang KE, Song HY, Jung JW, Oh SJ, Yoon KH, Park DS, Jeong ET, Kim HR. Pleural fluid characteristics of pleuropulmonary paragonimiasis masquerading as pleural tuberculosis. Korean J Intern Med. 2015 Jan;30(1):56-61. doi: 10.3904/kjim.2015.30.1.56. Epub 2014 Dec 30. PMID: 25589836; PMCID: PMC4293564.
Li KK, Jin GY, Kwon KS. What Findings on Chest CTs Can Delay Diagnosis of Pleuropulmonary Paragonimiasis? Tomography. 2022 Jun 9;8(3):1493-1502. doi: 10.3390/tomography8030122. PMID: 35736870; PMCID: PMC9228157.
Cho SY, Kim SI, Kang SY, Kong Y, Han SK, Shim YS, Han YC. Antibody changes in paragonimiasis patients after praziquantel treatment as observed by ELISA and immunoblot. Kisaengchunghak Chapchi. 1989 Mar;27(1):15-21. doi: 10.3347/kjp.1989.27.1.15. PMID: 2487259.
Knobloch J, Paz G, Feldmeier H, Wegner D, Voelker J. Serum antibody levels in human paragonimiasis before and after therapy with praziquantel. Trans R Soc Trop Med Hyg. 1984;78(6):835-6. doi: 10.1016/0035-9203(84)90038-5. PMID: 6533858.