Filarial Nematodes (Brugia, Dirofilaria, Loa, Mansonella, Onchocerca, Wuchereria) – Microscopy, Antibody, and Antigen

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 microscopy, antibody, and antigen testing information for filarial nematode infections at Public Health Ontario (PHO). Filarial nematode infections include: a) lymphatic filariasis (elephantiasis) caused by Wuchereria bancrofti or Brugia, b) loiasis (African eye worm) caused by Loa loa, c) dirofilariasis (dog heartworm) caused by Dirofilaria, d) onchocerciasis (river blindness) caused by Onchocerca volvulus, and mansonellosis due to Mansonella.

Lymphatic filariasis: Infections occur in tropical regions following mosquito bites. Manifestations include acute dermatolymphangioadenitis (ADLA), tropical pulmonary eosinophilia (TPE), chronic unilateral lymphedema, hydrocele, breast lump, and/or chyluria.

Loiasis: Infections occur in West and Central Africa following Chrysops deer fly bites. Manifestations include transient visible subconjunctival adult worms and chronic transient subcutaneous angioedema (“Calabar swellings”).

Dirofilariasis: Infections occur worldwide following mosquito bites. Manifestations include similar manifestations as loiasis or pulmonary nodules (“coin lesions”).

Onchocerciasis: Infections occur in sub-Saharan Africa, Yemen, Brazil, and Venezuela following Simulium black fly bites. Manifestations include chronic diffuse punctate keratitis, pruritic dermatitis, and subcutaneous nodules (“onchocercoma”).

Mansonellosis:Infections occur in Latin America and sub-Saharan Africa following midge or black fly bites. Manifestations are usually mild but may include keratitis, periorbital inflammation, pruritic dermatitis, serositis, or urticarial rashes.

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

Updates

Updated to consolidate microscopy and serology testing information into a single test information webpage.

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

Testing Indications

Microscopy and serology are indicated for the diagnosis of individuals with compatible clinical and epidemiological evidence of a filarial nematode infection.

Antigen testing is only available for Wuchereria but is not routinely performed at PHO. It is mainly used at PHO for known filarial antibody seropositive individuals with negative microscopy and symptom/exposure that are overlapping between lymphatic filariasis and other filarial nematode infections.

Other diagnostic methods, such as diethylcarbamazine (DEC) patch testing on skin and/or slit lamp examination on eyes, should be considered for some filarial nematodes but are not performed at PHO.

Note: there are currently no PCR tests available at PHO for filarial nematode infections.

Acceptance/Rejection Criteria

Testing will only be accepted in cases with both of the following information documented on the requisition:

Travel/migration from an endemic region
Signs or symptoms compatible with a filarial nematode infection

Wuchereria bancrofti antigen testing requests without PHO Microbiologist’s pre-approval will be rejected. If antigen testing is needed, contact the PHO Laboratory Customer Service at 416-235-6556 or 1-877-604-4567.

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Filarial nematodes - Microscopy	General Test Requisition	Whole blood AND Unstained, unfixed thick smear AND Unstained, methanol-fixed thin smear	2.0 ml 2 slides 2 slides	EDTA blood tube (labelled) Slide mailer (each slide individually labelled) Slide mailer (each slide individually labelled)
Filarial nematodes - Microscopy	General Test Requisition	Body fluid or tissue specimen (e.g. skin scrapings, nodule biopsy, urine, lymph node aspirate, hydrocele fluid)	1.0 ml (fluid) 0.2 g (tissue)	Sterile container
Filarial nematodes - Antibody	General Test Requisition	Blood or serum	5.0 ml blood or 1.0 ml serum	Blood, clotted – vacutainer tubes (SST)
Wuchereria bancrofti – Antigen (preapproval required)	General Test Requisition	Blood or serum	5.0 ml blood or 1.0 ml serum	Blood, clotted – vacutainer tubes (SST)

Submission and Collection Notes

Complete all fields of the requisition form.

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

Travel/migration from an endemic region
Signs or symptoms compatible with a filarial nematode infection

Label the specimen container(s), including the slide mailer itself and each individual slide, 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.

Refer to SPECIAL INSTRUCTIONS for detailed collection instructions.

Timing of Specimen Collection

For all filarial nematodes: Microscopy may be negative within the first 6 to 18 months post-exposure (i.e. prepatent period).

For lymphatic filariasis: Blood for microscopy should ideally be collected between the hours of 10 p.m. (22:00) and 2 a.m. (02:00) due to the nocturnal parasitemia periodicity seen in most cases of lymphatic filariasis.

For loiasis: Blood for microscopy should ideally be collected between the hours of 10 a.m. (10:00) and 2 p.m. (14:00) due to the diurnal parasitemia periodicity seen in most cases of loiasis.¹

Limitations

For serology and antigen testing: Grossly haemolysed, 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 in biohazard bag and seal. Serum specimens should be stored at 2-8°C.

Skin specimens should be sent to PHO’s Toronto site as soon as possible, ideally between Monday to Wednesday to avoid weekend storage. EDTA blood and skin tissue specimens should be stored at room temperature, as refrigeration can lead to distortion and loss of parasite morphology.

Other specimens should be sent to PHO within 48 hours of collection.

All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Special Instructions

For skin snip collection (e.g. for onchocerciasis or mansonellosis):

Identify the body sites where skin sampling will be performed. Note: Ideally, sampling would be performed in sites where the pruritic manifestations are most prominent, or from the buttock region (above the iliac crest), the shoulders (over the scapula), and/or the lower calves. Up to 6 skin sites should be sampled per patient to improve sensitivity.
If needed, apply a topical anesthetic agent to each skin site.
Disinfect the skin site with an alcohol-based disinfectant.
Using a sterile corneoscleral punch tool (e.g. Holth or Walser type), collect a 2-3 mm diameter bloodless skin biopsy sample. Alternatively, using the point of a sterile needle or lancet, gently pull the skin upward to create a small “cone” or “tent” of about 2-3 mm height, then shave off the raised area carefully using a sterile razor blade. Note: The skin snip should be thick enough to include the outer part of the dermal papillae, but thin enough so that no significant bleeding occurs (slight oozing of interstitial fluid may be present).
Transfer the skin snips into a small tube.
Add 2-3 drops of sterile normal (0.85%) physiological saline per skin snip into the tube.
Cover the skin snip site with an appropriate bandage/plaster. The site should heal within two to eight days.
Keep the sample at room temperature and send to PHO as soon as possible for examination within 24 hours.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Filarial nematodes microscopy is performed daily from Monday to Saturday at PHO’s Toronto site. Turnaround time for microscopy is up to 3 calendar days from receipt at PHO’s Toronto site.

Filarial nematodes serology and Wuchereria antigen testing are forwarded to the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time is up to 42 calendar days from receipt at PHO.

Test Methods

Microscopy: Microscopy is performed at PHO using Giemsa’s stain. Whole blood specimens undergo concentration by formalin lysis (“Knott’s concentration”). Parasitemia levels are reported as a ratio of parasites/ml using a direct 20 µl thick smear method.

Serology: Serology is performed at the NRCP using an enzyme-linked immunoassay (ELISA) based on antibody capture using crude Brugia malayi adult worm antigens.

Antigen: Wuchereria bancrofti antigen testing is performed at the NRCP using the BinaxNOW Filariasis Immunochromatographic Test (ICT) card for detection of a 200 kDa Wuchereria bancrofti adult circulating filarial antigen (CFA).

Performance and Limitations:
Microscopy sensitivity is usually under 50% for most filarial nematode infections. For lymphatic filariasis and loiasis, whole blood concentration (e.g. formalin lysis and/or nucleopore filtration) may increase sensitivity by an additional 20% or more. Sensitivity is highest during nighttime for lymphatic filariasis and daytime for loiasis, while periodicity is not described in other filarial nematode infections. Repeat collection may increase sensitivity over time. Due to the prepatent period, acute testing within 6 to 18 months after initial exposure may yield negative microscopy results. Recent treatment may further reduce sensitivity.^1-14

For serology, the NRCP reports a sensitivity of 91% and specificity of 84% for lymphatic filariasis. Sensitivity may be higher in Brugia infections compared to Wuchereria infections. Although limited evidence exists, cross-reactivity may occur with other filarial nematode infections. Cross-reactivity may also occur with non-filarial (e.g., Strongyloides, Schistosoma, Echinococcus) infections. False positive reactions may occur in patients with autoimmune disorders (e.g., rheumatoid arthritis). A positive result does not distinguish current from prior resolved infection, as antibodies may remain detectable for years.^1-15

For antigen testing, the BinaxNOW Filariasis ICT sensitivity is reported at around 75 to 90% for individuals with Wuchereria infection. Sensitivity may be lower in acute presentations, low intensity infections, or after exposure to mass drug administration. Cross-reactivity may occur with other filarial infections such as Loa, especially at high microfilaremia levels, but is not traditionally reported in Brugia infections. Although generally indicative of active infection, residual antigenemia may persist for up to 5 years following treatment and may be positive in infertile non-pathogenic Wuchereria infections.^12,14,16-21

Interpretation

For filarial nematodes microscopy (“Parasite microscopy”):

Parasite microscopy	Interpretation
Parasite(s) found	Active filarial nematode infection. The nematode name, stage(s), and parasitemia level (for whole blood samples) will be reported.
Parasite(s) not detected	Infection cannot be ruled out by a single specimen tested. If the initial testing result is negative and no alternate diagnosis is established, additional specimen(s) can be collected.

For filarial nematodes serology (“Filariasis by ELISA – Referred Out”):

Filariasis Sample Value	Interpretation	Comments
≥ 0.30	Positive	Filarial nematode antibodies detected. Does not distinguish between genera or species. Does not distinguish current from resolved or past infection. Cross-reactivity may occur with other helminths. Clinical correlation required.
0.20 to 0.29	Equivocal	Filarial nematode antibody status inconclusive. Repeat collection if clinically indicated.
< 0.20	Negative	Filarial nematode antibodies NOT detected. Does not rule out infection, especially if tested within the first 6 to 18 months of exposure. Repeat collection if clinically indicated.

For Wuchereria bancrofti antigen (“Wuchereria Antigen Test – Referred Out”):

Filaria Bancrofti antigen	Interpretation
Positive	Detectable level of Wuchereria bancrofti antigens. Does not distinguish active from recently treated (up to 5 years) or infertile worm infection. Cross-reactivity may occur with other filarial nematodes or other infections. Clinical correlation required.
Negative	No detectable level of Wuchereria bancrofti antigens. Does not rule out infection, especially if tested within the first 6 to 18 months of exposure. Repeat collection if clinically indicated.

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

Mathison BA, Couturier MR, Pritt BS. Diagnostic Identification and Differentiation of Microfilariae. J Clin Microbiol. 2019 Sep 24;57(10):e00706-19. doi: 10.1128/JCM.00706-19. PMID: 31340993; PMCID: PMC6760958.
Chesnais CB, Awaca-Uvon NP, Bolay FK, Boussinesq M, Fischer PU, Gankpala L, Meite A, Missamou F, Pion SD, Weil GJ. A multi-center field study of two point-of-care tests for circulating Wuchereria bancrofti antigenemia in Africa. PLoS Negl Trop Dis. 2017 Sep 11;11(9):e0005703. doi: 10.1371/journal.pntd.0005703. PMID: 28892473; PMCID: PMC5608416.
Hardy M, Samuela J, Kama M, Tuicakau M, Romani L, Whitfeld MJ, King CL, Weil GJ, Grobler AC, Robinson LJ, Kaldor JM, Steer AC. Individual Efficacy and Community Impact of Ivermectin, Diethylcarbamazine, and Albendazole Mass Drug Administration for Lymphatic Filariasis Control in Fiji: A Cluster Randomized Trial. Clin Infect Dis. 2021 Sep 15;73(6):994-1002. doi: 10.1093/cid/ciab202. PMID: 33728462.
Scott JL, Mayfield HJ, Sinclair JE, Martin BM, Howlett M, Muttucumaru R, Won KY, Thomsen R, Viali S, Tofaeono-Pifeleti R, Graves PM, Lau CL. Field laboratory comparison of STANDARD Q Filariasis Antigen Test (QFAT) with Bioline Filariasis Test Strip (FTS) for the detection of Lymphatic Filariasis in Samoa, 2023. PLoS Negl Trop Dis. 2024 Aug 5;18(8):e0012386. doi: 10.1371/journal.pntd.0012386. PMID: 39102429; PMCID: PMC11326698.
Dieki R, Nsi-Emvo E, Akue JP. The Human Filaria Loa loa: Update on Diagnostics and Immune Response. Res Rep Trop Med. 2022 Aug 1;13:41-54. doi: 10.2147/RRTM.S355104. PMID: 35936385; PMCID: PMC9355020.
Simón F, Siles-Lucas M, Morchón R, González-Miguel J, Mellado I, Carretón E, Montoya-Alonso JA. Human and animal dirofilariasis: the emergence of a zoonotic mosaic. Clin Microbiol Rev. 2012 Jul;25(3):507-44. doi: 10.1128/CMR.00012-12. PMID: 22763636; PMCID: PMC3416488.
Udall DN. Recent updates on onchocerciasis: diagnosis and treatment. Clin Infect Dis. 2007 Jan 1;44(1):53-60. doi: 10.1086/509325. Epub 2006 Nov 29. PMID: 17143815.
Bottomley C, Isham V, Vivas-Martínez S, Kuesel AC, Attah SK, Opoku NO, Lustigman S, Walker M, Basáñez MG. Modelling Neglected Tropical Diseases diagnostics: the sensitivity of skin snips for Onchocerca volvulus in near elimination and surveillance settings. Parasit Vectors. 2016 Jun 14;9(1):343. doi: 10.1186/s13071-016-1605-3. PMID: 27301567; PMCID: PMC4908809.
Dahmer KJ, Palma-Cuero M, Ciuoderis K, Patiño C, Roitman S, Li Z, Sinha A, Hite JL, Bellido Cuellar O, Hernandez-Ortiz JP, Osorio JE, Christensen BM, Carlow C, Zamanian M. Molecular surveillance detects high prevalence of the neglected parasite Mansonella ozzardi in the Colombian Amazon. medRxiv [Preprint]. 2023 May 11:2023.05.10.23289806. doi: 10.1101/2023.05.10.23289806. Update in: J Infect Dis. 2023 Nov 11;228(10):1441-1451. doi: 10.1093/infdis/jiad331. PMID: 37215049; PMCID: PMC10197819.
Courtney CH, Zeng QY. Relationship between microfilaria count and sensitivity of the direct smear for diagnosis of canine dirofilariosis. Vet Parasitol. 2001 Jan 1;94(3):199-204. doi: 10.1016/s0304-4017(00)00377-0. PMID: 11113550.
Rawlins SC, Chailett P, Ragoonanansingh RN, Baboolal S, Stroom V. Microscopical and serological diagnosis of Wuchereria bancrofti. West Indian Med J. 1994 Sep;43(3):75-9. PMID: 7817540.
World Health Organization (2016). Strengthening the assessment of lymphatic filariasis transmission and documenting the achievement of elimination. World Health Organization. https://iris.who.int/handle/10665/246176
Moulia-Pelat JP, Glaziou P, Nguyen-Ngoc L, Cardines D, Spiegel A, Cartel JL. A comparative study of detection methods for evaluation of microfilaremia in lymphatic filariasis control programmes. Trop Med Parasitol. 1992 Sep;43(3):146-8. PMID: 1470830.
Helmy H, Weil GJ, Ellethy AS, Ahmed ES, Setouhy ME, Ramzy RM. Bancroftian filariasis: effect of repeated treatment with diethylcarbamazine and albendazole on microfilaraemia, antigenaemia and antifilarial antibodies. Trans R Soc Trop Med Hyg. 2006 Jul;100(7):656-62. doi: 10.1016/j.trstmh.2005.08.015. Epub 2006 Jan 18. PMID: 16414095.
Vranjković MP, Vitko Havliček A, Kramar M, Balen Topić M, Beck D, Jurković Žilić D, Gagović E, Beck R. Not a Dead-End Host: First Confirmed Persistent Microfilaremia in Human Dirofilaria repens Infection. Microorganisms. 2025 Sep 26;13(10):2263. doi: 10.3390/microorganisms13102263. PMID: 41156723; PMCID: PMC12565814.
Bhumiratana A, Koyadun S, Suvannadabba S, Karnjanopas K, Rojanapremsuk J, Buddhirakkul P, Tantiwattanasup W. Field trial of the ICT filariasis for diagnosis of Wuchereria bancrofti infections in an endemic population of Thailand. Southeast Asian J Trop Med Public Health. 1999 Sep;30(3):562-8. PMID: 10774670.
Gass K, Beau de Rochars MV, Boakye D, Bradley M, Fischer PU, Gyapong J, Itoh M, Ituaso-Conway N, Joseph H, Kyelem D, Laney SJ, Legrand AM, Liyanage TS, Melrose W, Mohammed K, Pilotte N, Ottesen EA, Plichart C, Ramaiah K, Rao RU, Talbot J, Weil GJ, Williams SA, Won KY, Lammie P. A multicenter evaluation of diagnostic tools to define endpoints for programs to eliminate bancroftian filariasis. PLoS Negl Trop Dis. 2012 Jan;6(1):e1479. doi: 10.1371/journal.pntd.0001479. Epub 2012 Jan 17. PMID: 22272369; PMCID: PMC3260316.
Gounoue-Kamkumo R, Nana-Djeunga HC, Bopda J, Akame J, Tarini A, Kamgno J. Loss of sensitivity of immunochromatographic test (ICT) for lymphatic filariasis diagnosis in low prevalence settings: consequence in the monitoring and evaluation procedures. BMC Infect Dis. 2015 Dec 23;15:579. doi: 10.1186/s12879-015-1317-x. PMID: 26700472; PMCID: PMC4690254.
Pion SD, Montavon C, Chesnais CB, Kamgno J, Wanji S, Klion AD, Nutman TB, Boussinesq M. Positivity of Antigen Tests Used for Diagnosis of Lymphatic Filariasis in Individuals Without Wuchereria bancrofti Infection But with High Loa loa Microfilaremia. Am J Trop Med Hyg. 2016 Dec 7;95(6):1417-1423. doi: 10.4269/ajtmh.16-0547. Epub 2016 Oct 10. PMID: 27729568; PMCID: PMC5154460.
Graves PM, Scott JL, Berg Soto A, Widi AYN, Whittaker M, Lau CL, Won KY. Laboratory Comparison of Rapid Antigen Diagnostic Tests for Lymphatic Filariasis: STANDARD Q Filariasis Antigen Test (QFAT) Versus Bioline Filariasis Test Strip (FTS). Trop Med Infect Dis. 2025 Jan 14;10(1):23. doi: 10.3390/tropicalmed10010023. PMID: 39852674; PMCID: PMC11768758.
Mensah DA, Opoku VS, Boateng J, Opoku J, Osei-Mensah J, Gyasi C, Obeng P, Ahiadorme M, Atisu PD, Kutu ED, Kroidl I, Klarmann-Schulz U, Hoerauf A, Debrah LB, Debrah AY. Changes in circulating filarial antigen status in previously positive individuals: Lessons for treatment monitoring and pre-transmission assessment surveys. PLoS Negl Trop Dis. 2025 Feb 4;19(2):e0012802. doi: 10.1371/journal.pntd.0012802. PMID: 39903788; PMCID: PMC12129320.