Baylisascaris – Serology

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.

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

As of February 5, 2024, the acceptance criteria have been clarified.

Testing Indications

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.

Serology is only advised for individuals with compatible exposure history and clinical presentation. Baylisascariasis is usually acquired by ingesting infectious eggs from the environment. It takes at least 1 to 4 weeks after procyonid (e.g. racoon) or rarely canid feces deposition in the environment for eggs to become infectious. Manifestations may appear one to four weeks following ingestion. 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.

Acceptance/Rejection Criteria

Baylisascaris serology is only performed if information compatible with baylisascariasis is provided on the requisition, including both:

  • Exposure history (exposure to procyonid e.g. racoons or rarely canids e.g. dogs), and;
  • Clinical presentation (including any of the manifestations listed above)

Failure to provide this information may result in rejection or testing delay.

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 - Serum Separator Tube (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. Patient setting/population
  2. Test(s) requested and indication for testing
  3. Signs/symptoms including symptom onset date
  4. Relevant exposure

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 exposure event occurred recently.


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

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. 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 requests are forwarded to the National Reference Centre for Parasitology (NRCP). Turnaround time is up to 42 days from receipt by PHO’s laboratory.

Test Methods

Baylisascaris serology 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).

Performance and Limitations:
The performance of the 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 infection1. 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 remote infection, with seroprevalence estimates at 6.9% in the general population in the US and 5.7% in wildlife rehabilitators in North America2,3. Therefore, testing should only be considered if there is a compatible suspicion of active disease.


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 is advised.


Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.


  1. 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.
  2. 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.
  3. 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.
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Updated 23 Feb 2024