Baylisascaris – Serology

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Testing Indications

This page provides routine serology (antibody) testing information for baylisascariasis at Public Health Ontario (PHO). The causative agents of baylisascariasis is Baylisascaris procyonis (procyonid definitive hosts, e.g. raccoons). Baylisascariasis manifestations include neural larva migrans (NLM), visceral larva migrans (VLM), and ocular larva migrans (OLM).

Testing options:
Serology is the main non-invasive laboratory diagnostic modality available for baylisascariasis. In addition to serology, larvae can also be found in histologic tissue sections, but biopsies may not always retrieve the migrating larvae (up to 1.8 mm long and 70 µm wide). Molecular testing is currently not routinely available in clinical laboratories.

Who to test:
Testing is only advised for individuals with compatible exposure history and clinical presentation. Baylisascariasis is primarily found in the Americas, Europe, and Asia, particularly in children, and is usually acquired by ingestion of embryonated eggs from the surrounding environment. Incubation may take 1 to 4 weeks. NLM manifestations may include ill-defined lesions on imaging, eosinophilic meningoencephalitis, myelitis, vasculitis, or radiculitis. VLM manifestations depend on the organ affected and may include multiple ill-defined visceral granulomatous lesions on imaging, eosinophilia, urticarial rash, fever, anorexia, hepatitis, pneumonitis, myalgia, or carditis. OLM manifestations may include unilateral granulomatous lesions on fundoscopy, uveitis, retinitis, or endophthalmitis.

Testing update (September 7, 2022):
Cerebrospinal fluid (CSF) is now listed as a specimen type available upon request after approval by the PHO microbiologist. This specimen type is not validated therefore results should be interpreted with caution.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

Baylisascaris - Serology

Whole blood or Serum

5.0 ml blood or 1.0 ml serum

Blood, clotted - vacutainer tubes (SST)

Baylisascaris - Serology

Cerebrospinal fluid (CSF) if available, upon approval

1.0 ml

Sterile container

Submission and Collection Notes


Complete all fields of the General Test Requisition Form, including:

    1. Test(s) requested and indication for testing
    2. Animal exposure history (i.e. raccoon)
    3. Clinical information including symptom onset date
    4. Patient setting/population

Important: symptoms, onset date, and animal exposure history are required acceptance criteria for testing. Make sure to include this information in the requisition. Failure to provide this information may result in rejection or testing delay.


Label the specimen container 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 specimens: Although CSF specimens have not been validated, they may be positive in suspected cases. This specimen type requires approval, please contact the PHO microbiologist for information.

Timing of Specimen Collection

An acute (collected early after the onset of symptoms) and a convalescent (collected 2-3 weeks later) may be required for laboratory diagnosis if the procyonid exposure event occurred recently.


Haemolysed, icteric, lipemic or microbial contaminated sera are not recommended for testing.

The performance of the National Reference Centre for Parasitology (NRCP) in-house Western blot assay, co-validated with the US Centers for Disease Control and Prevention (CDC), has been reported at 88% sensitivity and 98% specificity for Baylisascaris procyonis infection (Rascoe et al., Clin Vaccine Immunol 2013). There were rare isolated cross-reactivity events with single cases of malaria, giardiasis, filariasis, and strongyloidiasis, but no cross-reactivity seen with toxocariasis (a common differential diagnostic etiology).

Antibody detection may also represent asymptomatic co-infection or past infection, with seroprevalence estimates at 6.9% in the general population in the US and 5.7% in wildlife rehabilitators in North America (Sapp et al., Emerg Infect Dis 2016; Weinstein et al. Emerg Infect Dis 2017).

Storage and Transport

Centrifuge tube if using serum separator tube (SST). Place specimen in biohazard bag and seal.

Specimens should be stored at 2-8°C following collection and shipped to the PHO’s laboratory on ice packs as soon as possible.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Turnaround time is up to 42 days from receipt by PHO’s laboratory.

Test Methods

Baylisascaris serology test is a referred-out test. It is performed at the NRCP by Western blot assay using a recombinant Baylisascaris procyonis RAG1 protein(rBpRAG1) derived from the L3 stage of the parasite and purified from E. coli BL21 containing pRSET C/RAG1 plasmids. The assay provides a qualitative value (negative or positive).


A negative result suggests no detectable level of antibody against Baylisascaris procyonis.

A positive result suggests detectable level of antibody against Baylisascaris procyonis. Clinical and exposure correlation to procyonids or procyonid feces is advised.


Results are reported to the ordering physician or health care provider as indicated on the requisition.

Additional Information

Patient Clinical information is required for the sample to be processed for serology testing.

Mis à jour le 13 sept. 2022