Schistosoma – Serology

This document provides routine serology (antibody) testing information for schistosomiasis (also known as bilharzia) at Public Health Ontario (PHO). The causative agents of schistosomiasis include Schistosoma mansoni (Africa and South America), S. japonicum (East Asia), S. mekongi (Southeast Asia), S. haematobium (Africa and the Middle East), S. intercalatum (West and Central Africa), and S. guineensis (West and Central Africa).

The test information described below is limited to serologic testing. For microscopy, please refer to the following links:

Who to test:
Microscopy is the gold standard diagnostic test for schistosomiasis and should be requested whenever testing is indicated. Serologic testing is an adjunct to microscopy for individuals with clinical or epidemiologic risk factors of schistosomiasis, particularly for individuals with low parasite burden when microscopy is negative.

Test updates (as of July 20, 2022):
PHO has changed its Schistosoma spp. serologic testing assay from the SciMedx Schistosomiasis Serology Microwell ELISA (SciMedx Corp. Denville, US) to the EUROIMMUN Anti-Schistosoma ELISA (IgG) (EUROIMMUN AG, Luebek, Germany).

Specimen Collection and Handling

Specimen Requirements

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

Schistosoma spp. IgG - Serology

Serum

5.0 ml blood or 1.0 ml serum

Clotted vacutainer blood tubes (SST)

Submission and Collection Notes

1

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

  1. Test(s) requested and indication for testing
  2. Travel history (if applicable)
  3. Clinical information including symptom onset date or if asymptomatic
  4. Patient setting/population
2

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.

Limitations

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

The current manufacturer reports 95% positive percent agreement and 87% negative percent agreement compared to an external quality assurance scheme (indeterminate results included). PHO’s internal verification had 98% positive percent agreement and 91% negative percent agreement compared to a prior assay (SciMedx) and/or the National Reference Centre for Parasitology (NRCP) in-house ELISA (indeterminate results included).

Assay performance may vary depending on the stage of infection (e.g., acute vs. chronic). Reported seropositivity most commonly appears 6-12 weeks after initial exposure, but there have been occasional reports of late seroconversion up to 20-24 weeks post-exposure (Jones et al., 1992; Soentjens et al., 2014). Serology may remain positive for years after praziquantel therapy (Bligh et al., 2010; Soentjens et al., 2014) and may not be able to distinguish between active, resolved, or recurrent infection.

Assay performance by individual species has not been evaluated and may vary, however cross-reactivity has been described for other Schistosoma mansoni soluble egg antigens (SmSEA)-based assays between S. mansoni, S. japonicum, S. mekongi and S. haematobium (Smith et al., 2012; Nickel et al., 2015). This assay does not provide discrimination between species. Cross-reactivity has been reported with other helminths (e.g., Strongyloides, hookworms, Trichinella, Trichuris, filarial nematodes, Fasciola, Opisthorchis, or Echinococcus).

Preparation Prior to 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)

Schistosoma spp. serology testing is performed once per week.

Turnaround time is up to 10 days from receipt at PHO’s laboratory.

Reporting

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

Test Methods

Schistosoma spp. serology test is performed using a Health Canada licensed commercial enzyme-linked immunosorbent assay (ELISA), the EUROIMMUN Anti-Schistosoma ELISA (IgG). The assay uses highly purified SmSEA. The assay provides a semi-quantitative value based on the ratio between the extinction of the control signal and extinction of the calibrator signal.

Interpretation

Ratio IgG Result Interpretation
<0.8 Non-reactive No detectable level of antibody against Schistosoma spp.
≥0.8 to <1.1 Indeterminate Schistosoma spp. antibody status inconclusive. Clinical/exposure correlation is required. Treatment and/or repeat testing may be advised depending on the patient’s risk status.
≥1.1 Reactive Detectable level of antibody against Schistosoma spp. Cross-reactivity may occur with other helminths including Strongyloides, Trichinella, Trichuris, Echinoccus, and filarial nematodes. Clinical and exposure correlation is advised, with further testing as appropriate.

Mis à jour le 21 juill. 2022