Baylisascaris (Baylisascariasis) – Antibody

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Background
This page provides antibody (serology) testing information for baylisascariasis at Public Health Ontario (PHO). The causative agent of baylisascariasis is the parasitic larval nematode Baylisascaris procyonis (procyonid definitive host). Infections occur worldwide, particularly in children and young adults, following ingestion of infectious eggs from the environment contaminated by procyonid (e.g. racoon) or canid feces. It takes at least 1 to 4 weeks after procyonid or canid feces deposition in the environment for eggs to become infectious.Baylisascariasis manifestations include neural larva migrans (NLM), visceral larva migrans (VLM), and ocular larva migrans (OLM). NLM manifestations include eosinophilic meningoencephalitis, myelitis, vasculitis, or radiculitis. Non-specific hypodense or ring-enhancing lesions may be seen on brain 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.

Updates

Additional information around acceptance criteria as well as performance and limitations had been added.

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

Testing Indications

Serology may be considered for the diagnosis of individuals with compatible exposure history and clinical presentation for baylisascariasis. The larvae may be identifiable on fundoscopy, or less frequently by tissue biopsy with histopathology.

Note: Baylisascaris 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 procyonids or procyonid latrines
Clinical signs or symptoms consistent with baylisascariasis
Eosinophilia, eosinophilic pleocytosis, or ocular lesion(s)

Specimen Collection and Handling

Specimen Requirements

Test Requested

Required Requisition(s)

Specimen Type

Minimum Volume

Collection Kit

Baylisascaris - Antibody

General Test Requisition

Serum

Cerebrospinal fluid (CSF)

Ocular fluid (e.g. aqueous humor)

1.0 ml

Red top (clotted) tube or serum separator tube (SST)

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 procyonids or procyonid latrines
Clinical signs or symptoms consistent with baylisascariasis
Eosinophilia, eosinophilic pleocytosis, or ocular lesion(s)

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.

CSF antibodies may be detectable in patients with NLM, ocular fluid antibodies may be detectable in patients with OLM, but neither are validated specimen types for this test and require approval. If needed, contact PHO’s customer service for information.

Timing of Specimen Collection

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

Limitations

Grossly haemolyzed, lipemic, contaminated specimens, and specimens containing anti-coagulant are unsuitable for testing.

Storage and Transport

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)

Baylisascaris antibody testing is referred out to the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time for antibody testing is up to 30 calendar days from receipt at PHO.

Test Methods

Baylisascaris antibody testing is performed at the NRCP using a Western blot assay based on recombinant Baylisascaris procyonis L3 larva repeated antigen 1 protein (rBpRAG1).

Performance and Limitations:
Baylisascaris antibody testing performance is reported to have 88% sensitivity and 98% specificity by the NRCP. Performance may vary by clinical presentation (e.g. OLM versus VLM). The accuracy of antibody testing on ocular or CSF samples is not established but detection has been reported in some cases. Cross-reactivity has been rarely described with malaria, giardiasis, filariasis, and strongyloidiasis, but no cross-reactivity has been reported with toxocariasis. Antibody detection may also represent asymptomatic co-infection or remote infection, with seroprevalence estimates at 6.9% in the general population in the US and 5.7% in wildlife rehabilitators in North America. Therefore, testing should only be considered if there is a compatible suspicion of active disease. The assay may remain positive for years after infection and may not be able to distinguish between active, resolved, or recurrent infection.^1-4

Interpretation

For Baylisascaris antibody testing results (“Baylisascariasis – Referred Out”):

Baylisascariasis Immunoblot	Interpretation
Positive	Baylisascaris antibodies detected. Cross-reactivity may occur with other infections. May not distinguish between active, resolved, or recurrent infection.
Equivocal	Baylisascaris antibody status inconclusive. Clinical/exposure correlation required and repeat testing may be considered if clinically indicated.
Negative	Baylisascaris antibodies NOT detected. If recent infection is suspected, collection of a convalescent serum sample 2-3 weeks later is recommended to assess for seroconversion.

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

Rascoe LN, Santamaria C, Handali S, Dangoudoubiyam S, Kazacos KR, Wilkins PP, Ndao M. Interlaboratory optimization and evaluation of a serological assay for diagnosis of human baylisascariasis. Clin Vaccine Immunol. 2013 Nov; 20(11):1758-63. doi: 10.1128/CVI.00387-13. Epub 2013 Sep 18.
Sapp SG, Rascoe LN, Wilkins PP, Handali S, Gray EB, Eberhard M, Woodhall DM, Montgomery SP, Bailey KL, Lankau EW, Yabsley MJ. Baylisascaris procyonis Roundworm Seroprevalence among Wildlife Rehabilitators, United States and Canada, 2012-2015. Emerg Infect Dis. 2016 Dec; 22(12):2128-2131. doi: 10.3201/eid2212.160467.
Weinstein SB, Lake CM, Chastain HM, Fisk D, Handali S, Kahn PL, Montgomery SP, Wilkins PP, Kuris AM, Lafferty KD. Seroprevalence of Baylisascaris procyonis Infection among Humans, Santa Barbara County, California, USA, 2014-2016. Emerg Infect Dis. 2017 Aug; 23(8):1397-1399. doi: 10.3201/eid2308.170222.
Graeff-Teixeira C, Morassutti AL, Kazacos KR. Update on Baylisascariasis, a Highly Pathogenic Zoonotic Infection. Clin Microbiol Rev. 2016 Apr;29(2):375-99. doi: 10.1128/CMR.00044-15. PMID: 26960940; PMCID: PMC4786883.