Gnathostoma (Gnathostomiasis) – Antibody and 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 antibody (serology) and microscopy testing information for gnathostomiasis (also known as larva migrans profundus) at Public Health Ontario (PHO). The causative agent of gnathostomiasis is the parasitic larval nematode Gnathostoma. Infections mainly occur in subtropical and tropical regions following ingestion of undercooked fish, amphibians, reptiles, or birds. Gnathostomiasis manifestations include neural larva migrans (NLM), visceral larva migrans (VLM), ocular larva migrans (OLM), and cutaneous larva migrans (CLM). NLM manifestations include eosinophilic meningoencephalitis (often fulminant with or xanthochromic pleocytosis), myelitis, vasculitis, or radiculitis. Hemorrhagic lesions and/or larval tracks may be seen on imaging. VLM manifestations depend on the organ affected and may include multiple ill-defined visceral granulomatous lesions, eosinophilia, urticarial rash, fever, hepatitis, pneumonitis, myalgia, or carditis. OLM manifestations may include uveitis, diffuse unilateral subacute neuroretinitis (DUSN), or endophthalmitis. CLM manifestations may be chronic and intermittent over years and include migratory panniculitis, angioedema, or erythematous/necrotic tracking.

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

*Uncontrolled print copy. Valid only on day of print: 19 Oct 2026.

Testing Indications

Serology may be considered for the diagnosis of individuals with compatible exposure history and clinical presentation for gnathostomiasis. The larvae are usually identifiable on fundoscopy in OLM cases. In uncommon instances, the larvae may be retrieved from body fluids or tissues affected during larval migration, but CSF microscopy is usually negative.

Note: Gnathostoma PCR is not available at PHO.

Acceptance/Rejection Criteria

Testing will only be performed when all the following criteria are documented on the requisition form:

Exposure to undercooked fish, amphibians, reptiles, or birds
Clinical signs or symptoms consistent with gnathostomiasis
Eosinophilia, eosinophilic pleocytosis, or ocular lesion(s)

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Gnathostoma – Antibody	General Test Requisition	Serum	1.0 ml	Red top (clotted) tube or serum separator tube (SST)
Gnathostoma – Microscopy	General Test Requisition	Body fluid or tissue specimen	1.0 ml (fluid) or 0.2 (tissue)	Sterile container

Submission and Collection Notes

Complete all fields of the requisition form.

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

Exposure to undercooked fish, amphibians, reptiles, or birds
Clinical signs or symptoms consistent with gnathostomiasis
Eosinophilia, eosinophilic pleocytosis, or ocular lesions

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.

CSF antibodies may be detectable in patients with NLM, but it is not a validated specimen type for this test and requires approval. If needed, contact PHO’s customer service for information.

Timing of Specimen Collection

For serology: If a recent infection is suspected following exposure, repeat collection of a convalescent (2-3 weeks later) serum sample may be beneficial since serology may be negative in the acute phase of illness.

Limitations

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

Storage and Transport

For serology: Centrifuge tube if using serum separator tube (SST).

Place specimen container in a biohazard bag and properly seal the bag. Specimens should be stored at 2-8°C and shipped to PHO on ice packs within 48 hours of collection. All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Gnathostoma antibody testing is referred out to the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time for antibody testing is up to 60 calendar days from receipt at PHO. Gnathostoma microscopy is performed daily from Monday to Friday at PHO‘s laboratory-Toronto. Turnaround time for microscopy is up to 3 calendar days from receipt at PHO.

Test Methods

Gnathostoma antibody testing is performed at the NRCP using an enzyme-linked immunosorbent assay (ELISA) based on recombinant antigens.

Gnathostoma microscopy is performed at PHO using direct wet mount.

Performance and Limitations:
Gnathostoma antibody testing performance is reported to have 93% sensitivity and 100% specificity by the NRCP. Depending on the type of antigen source used in other antibody assays, sensitivity has been reported to range from 60-100% and specificity from 70-100%, with cross-reactivity reported with other helminth infections. Test performance may vary by Gnathostoma species and clinical presentation (e.g. CLM versus NLM). The accuracy of antibody testing on CSF samples is not established but detection has been reported in some cases. The assay may remain positive for years after infection and may not be able to distinguish between active, resolved, or recurrent infection.^1-12

Gnathostoma microscopy in CSF is usually negative. In some instances, larvae may be found and extracted from ocular compartments (OLM) or skin lesions (CLM), the latter being potentially enhanced during treatment due to the superficial larval migration into papules. Otherwise, if tissue material is biopsied, organisms may be found by histopathology if locally available.^13-14

Interpretation

For Gnathostoma antibody testing (“Gnathostomiasis by EIA – Referred Out”):

Gnathostomiasis EIA Sample Value	Result	Interpretation
> 1.5	Positive	Gnathostoma antibodies detected. Does not distinguish between species. Cross-reactivity may occur with other helminth infections. May not distinguish between active, resolved, or recurrent infection.
1.0 to 1.5	Equivocal	Gnathostoma antibody status inconclusive. Clinical/exposure correlation required and repeat testing may be considered if clinically indicated.
< 1.0	Negative	Gnathostoma antibodies NOT detected. If recent infection is suspected, collection of a convalescent serum sample 2-3 weeks later is recommended to assess for seroconversion.

For Gnathostoma microscopy (“Parasite microscopy”)”

Parasite Microscopy	Interpretation
Parasite(s) found Gnathostoma species	Active Gnathostoma infection. Does not distinguish between species.
Parasite(s) not detected	No evidence of Gnathostoma by microscopy. Does not rule out infection.

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

Saenseeha S, Penchom J, Yamasaki H, Laummaunwai P, Tayapiwatana C, Kitkhuandee A, Maleewong W, Intapan PM. A dot-ELISA test using a Gnathostoma spinigerum recombinant matrix metalloproteinase protein for the serodiagnosis of human gnathostomiasis. Southeast Asian J Trop Med Public Health. 2014 Sep;45(5):990-6. PMID: 25417498.
Katchanov J, Sawanyawisuth K, Chotmongkoi V, Nawa Y. Neurognathostomiasis, a neglected parasitosis of the central nervous system. Emerg Infect Dis. 2011 Jul;17(7):1174-80. doi: 10.3201/eid1707.101433. PMID: 21762569; PMCID: PMC3321562.
Suntharasamai P, Desakorn V, Migasena S, Bunnag D, Harinasuta T. ELISA for immunodiagnosis of human gnathostomiasis. Southeast Asian J Trop Med Public Health. 1985 Jun;16(2):274-9.
Janwan P, Intapan PM, Yamasaki H, Laummaunwai P, Sawanyawisuth K, Wongkham C, Tayapiwatana C, Kitkhuandee A, Lulitanond V, Nawa Y, Maleewong W. A recombinant matrix metalloproteinase protein from Gnathostoma spinigerum for serodiagnosis of neurognathostomiasis. Korean J Parasitol. 2013 Dec;51(6):751-4. doi: 10.3347/kjp.2013.51.6.751. Epub 2013 Dec 31. PMID: 24516285; PMCID: PMC3916469.
Ieamsuwan I, Watthanakulpanich D, Chaisri U, Adisakwattana P, Dekumyoy P. Evaluation of immunodiagnostic tests for human gnathostomiasis using different antigen preparations of Gnathostoma spinigerum larvae against IgE, IgM, IgG, IgG1-4 and IgG1 patterns of post-treated patients. Trop Med Int Health. 2021 Dec;26(12):1634-1644. doi: 10.1111/tmi.13679. Epub 2021 Sep 21. PMID: 34510662; PMCID: PMC9291276.
Diaz Camacho SP, Zazueta Ramos M, Ponce Torrecillas E, Osuna Ramirez I, Castro Velazquez R, Flores Gaxiola A, Baquera Heredia J, Willms K, Akahane H, Ogata K, Nawa Y. Clinical manifestations and immunodiagnosis of gnathostomiasis in Culiacan, Mexico. Am J Trop Med Hyg. 1998 Dec;59(6):908-15. doi: 10.4269/ajtmh.1998.59.908. PMID: 9886199.
Dharmkrong-at A, Migasena S, Suntharasamai P, Bunnag D, Priwan R, Sirisinha S. Enzyme-linked immunosorbent assay for detection of antibody to Gnathostoma antigen in patients with intermittent cutaneous migratory swelling. J Clin Microbiol. 1986 May;23(5):847-51. doi: 10.1128/jcm.23.5.847-851.1986. PMID: 3711272; PMCID: PMC268735.
Tada I, Araki T, Matsuda H, Araki K, Akahane H, Mimori T. A study on immunodiagnosis of gnathostomiasis by ELISA and double diffusion with special reference to the antigenicity of Gnathostoma doloresi. Southeast Asian J Trop Med Public Health. 1987 Dec;18(4):444-8. PMID: 3129795.
Nuchprayoon S, Sanprasert V, Suntravat M, Kraivichian K, Saksirisampant W, Nuchprayoon I. Study of specific IgG subclass antibodies for diagnosis of Gnathostoma spinigerum. Parasitol Res. 2003 Sep;91(2):137-43. doi: 10.1007/s00436-003-0947-x. Epub 2003 Aug 9. PMID: 12910416.
Nopparatana C, Setasuban P, Chaicumpa W, Tapchaisri P. Purification of Gnathostoma spinigerum specific antigen and immunodiagnosis of human gnathostomiasis. Int J Parasitol. 1991 Oct;21(6):677-87. doi: 10.1016/0020-7519(91)90079-m. PMID: 1757195.
Mimori Y, Tada I, Kawabata M, Ollague WL, Calero GH, De Chong YF. Immunodiagnosis of human gnathostomiasis in Ecuarodr by skin test and ELISA using Gnathostoma doloresi antigen. Jpn J Trop Med. 1987;15(3):191-6.
Tuntipopipat S, Chawengkiattikul R, Witoonpanich R, Chiemchanya S, Sirisinha S. Antigens, antibodies and immune complexes in cerebrospinal fluid of patients with cerebral gnathostomiasis. Southeast Asian J Trop Med Public Health. 1989 Sep;20(3):439-46. PMID: 2633352.
Karkhur S, Gupta A. Ocular Gnathostomiasis. N Engl J Med. 2025 Aug 14;393(7):e9. doi: 10.1056/NEJMicm2502742. Epub 2025 Aug 9. PMID: 40787913.
Bravo F, Gontijo B. Gnathostomiasis: an emerging infectious disease relevant to all dermatologists. An Bras Dermatol. 2018 Mar;93(2):172-180. doi: 10.1590/abd1806-4841.20187498. PMID: 29723377; PMCID: PMC5916386.