Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 16 peer-reviewed journal articles Updated
Pediatrics

Understanding the Diagnosis: Blood Tests and Imaging

At a Glance

Diagnosing toxocariasis requires a combination of blood tests and imaging. Doctors look for high eosinophil counts and positive TES-ELISA antibody tests, often confirmed by a Western Blot. CT or MRI scans may also reveal inflammation tracks left by larvae in the organs.

Diagnosing toxocariasis is rarely as simple as finding a parasite under a microscope. Because the larvae are microscopic and hidden deep within human tissue, doctors rely on “clues” from blood work and imaging to build a case for the diagnosis [1][2].

1. The CBC: Checking for “Eosinophilia”

One of the first things a doctor looks at is a Complete Blood Count (CBC). They are specifically looking for eosinophilia—an unusually high number of eosinophils (a type of white blood cell) [3].

  • A Key Marker: In Visceral Larva Migrans (VLM) and Covert Toxocariasis, the body often produces massive numbers of these cells to fight the larvae [4][5].
  • The Exception: In Ocular Larva Migrans (OLM), where only a single larva may be present in the eye, the blood eosinophil count might be completely normal [6].
  • Tracking Progress: If your child begins treatment, the doctor may use the absolute eosinophil count (AEC) to track if the infection is subsiding [7].

2. The Antibody Test: TES-ELISA

The standard test for this infection is the TES-ELISA. This test looks for antibodies (proteins the immune system makes) against the Toxocara Excretory-Secretory (TES) antigens—the substances the larvae release as they migrate [1][8].

  • Understanding “Cross-Reactivity”: A positive result doesn’t always mean your child has toxocariasis. The immune system sometimes makes similar-looking antibodies for other parasites, like Ascaris (common roundworms). This is called cross-reactivity and can lead to a “false positive” [9][10].
  • Improving Accuracy: Modern tests have been “cleaned” to remove components that used to cause false positives, making the tests much more accurate [11].
  • The “Two-Step” Rule: Many experts recommend a two-step process: a positive ELISA should be confirmed with a more specific test called a Western Blot to ensure the diagnosis is correct [9][1].

3. Imaging: Seeing the Larvae’s Path

While doctors can’t usually see the larvae themselves on a scan, they can see the “tracks” or inflammation the larvae leave behind.

  • Liver (CT/MRI): In VLM, scans may show multiple small, ill-defined (fuzzy-edged) lesions in the liver. These are usually less than 2cm in size and are areas of inflammation where the larvae have traveled [12][13].
  • Lungs (CT): If a child has a persistent cough, a chest scan might show small nodules or “cloudy” patches (opacities) that shift or change over time as the larvae move [14][15].

Lab Report Checklist for Parents

When reviewing your child’s records, look for these key terms:

  1. Absolute Eosinophil Count (AEC): Is it higher than the “normal” range listed by the lab?
  2. Toxocara IgG (ELISA): Is it listed as “Positive,” “Reactive,” or “Equivocal”?
  3. Toxocara Western Blot: If the ELISA was positive, was this second, more specific test performed?
  4. Hepatomegaly: A medical term for an enlarged liver, often noted on ultrasound or CT reports [5].

A diagnosis is usually made by combining these lab results with your child’s symptoms and history (like exposure to pets or dirt) [16]. If results are confusing, it is often because the infection is “moving” or the immune system is still reacting to a past exposure. To understand what happens once a diagnosis is confirmed, continue to Managing the Infection.

Common questions in this guide

What does a high eosinophil count mean on my child's CBC?
A high eosinophil count, or eosinophilia, is a common sign that the body is fighting a parasite. In visceral larva migrans, the immune system produces massive numbers of these white blood cells to attack the migrating larvae.
Can my child have ocular larva migrans with a negative blood test?
Yes, it is very possible. Because ocular larva migrans often involves only a single larva in the eye, it may not trigger a strong enough immune response to cause elevated eosinophils or a positive antibody test.
What does a positive TES-ELISA test result mean?
A positive TES-ELISA test means your child has antibodies to the Toxocara parasite. However, because it can sometimes falsely react to other common roundworms, doctors often order a Western Blot test to confirm the exact diagnosis.
Can imaging scans show the actual toxocariasis larvae?
No, doctors usually cannot see the microscopic larvae on a CT or MRI scan. Instead, the scans show the inflammation, fuzzy-edged lesions, or tracks that the larvae leave behind in organs like the liver and lungs.
How do doctors track if toxocariasis treatment is working?
Doctors often monitor the absolute eosinophil count (AEC) over time through routine blood work. If the infection is subsiding and the treatment is working, these white blood cell numbers will typically start to decrease.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What was the specific 'Absolute Eosinophil Count' (AEC) on my child's latest blood test, and how does it compare to previous results?
  2. 2.If the ELISA test came back positive, should we perform a Western Blot test to confirm it and rule out cross-reactivity with other parasites?
  3. 3.My child has a negative blood test, but we are seeing eye symptoms. Is it possible for the ELISA to be negative in cases of Ocular Larva Migrans?
  4. 4.If imaging (CT or MRI) shows liver or lung lesions, are they 'ill-defined,' which is common for this infection, or do they look like something else?
  5. 5.Will we use blood tests like the eosinophil count to monitor how well the treatment is working?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
  1. 1

    Evaluation of new Toxocara canis chimeric antigens as an alternative to conventional TES-Ag for anti-Toxocara antibodies detection.

    Mesa-Arango JA, Olave-Velandia AM, García-Montoya GM, et al.

    Heliyon 2022; (8(10)):e11144 doi:10.1016/j.heliyon.2022.e11144.

    PMID: 36299519
  2. 2

    Development of a Luminex Bead Based Assay for Diagnosis of Toxocariasis Using Recombinant Antigens Tc-CTL-1 and Tc-TES-26.

    Anderson JP, Rascoe LN, Levert K, et al.

    PLoS neglected tropical diseases 2015; (9(10)):e0004168 doi:10.1371/journal.pntd.0004168.

    PMID: 26485145
  3. 3

    [Visceral larva migrans syndrome and hepatic abscess: A case report].

    Arighi P, Hausbauer GE, Vázquez MG, Nastri M

    Archivos argentinos de pediatria 2018; (116(6)):e753-e756 doi:10.5546/aap.2018.e753.

    PMID: 30457730
  4. 4

    Clinical and Laboratory Findings among Patients with Toxocariasis in Medic Medical Center, Ho Chi Minh City, Vietnam in 2017-2019.

    Phuc LDV, Loi CB, Quang HH, et al.

    Iranian journal of parasitology 2021; (16(4)):538-547 doi:10.18502/ijpa.v16i4.7864.

    PMID: 35082881
  5. 5

    Hepatic Visceral Larva Migrans Causing Hepatic Venous Thrombosis and Prolonged Fever.

    Kaur J, Gupta A, Wadhwa N

    Indian pediatrics 2017; (54(10)):882-884 doi:10.1007/s13312-017-1155-6.

    PMID: 29120339
  6. 6

    [Atypical ocular toxocariasis in a child: A case report].

    Krichene MA, Hasnaoui I, Hassina S, et al.

    Journal francais d'ophtalmologie 2024; (47(6)):104191 doi:10.1016/j.jfo.2024.104191.

    PMID: 38713931
  7. 7

    Hepatic visceral larva migrans, a resilient entity on imaging: Experience from a tertiary liver center.

    Laroia ST, Rastogi A, Bihari C, et al.

    Tropical parasitology 2016; (6(1)):56-68 doi:10.4103/2229-5070.175100.

    PMID: 26998435
  8. 8

    Production of Toxocara cati TES-120 Recombinant Antigen and Comparison with its T. canis Homolog for Serodiagnosis of Toxocariasis.

    Zahabiun F, Sadjjadi SM, Yunus MH, et al.

    The American journal of tropical medicine and hygiene 2015; (93(2)):319-25 doi:10.4269/ajtmh.15-0190.

    PMID: 26033026
  9. 9

    Toxocariasis in internationally adopted children: Seroprevalence, diagnostic and therapeutic strategies.

    Monti N, Manciulli T, Bianchi L, et al.

    International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases 2026; (165()):108448 doi:10.1016/j.ijid.2026.108448.

    PMID: 41633426
  10. 10

    A new ELISA and western blot technique based on recombinant TES antigen and/or larval antigen for the detection of toxocariasis in humans.

    Raulf MK, Jordan D, Auer H, et al.

    Parasitology 2021; (148(3)):333-340 doi:10.1017/S0031182020002085.

    PMID: 33092663
  11. 11

    Deglycosylation of Excretory-Secretory Antigens of the Second-Stage Larvae of Toxocara cati Improves Its Efficacy in the Diagnosis of Human Toxocariasis.

    Pouryousef A, Sarkari B, Mootabi Alavi A, et al.

    Journal of tropical medicine 2023; (2023()):3024063 doi:10.1155/2023/3024063.

    PMID: 37492799
  12. 12

    HEPATIC VISCERAL LARVA MIGRANS DUE TO TOXOCARA CANIS IN A 72-YEAR-OLD MAN.

    Ko KD, Lee JJ, Kim KK, et al.

    The Southeast Asian journal of tropical medicine and public health 2015; (46(2)):181-3.

    PMID: 26513919
  13. 13

    Atypical Toxocara canis-Induced Hepatic Visceral Larva Migrans: Diagnostic Challenges and Literature Review.

    Huynh TM, Tran KQL, Dinh TH, et al.

    The Korean journal of gastroenterology = Taehan Sohwagi Hakhoe chi 2024; (83(6)):247-252 doi:10.4166/kjg.2024.051.

    PMID: 38918038
  14. 14

    Presumptive pulmonary toxocariasis in a patient affected by acute myeloid leukemia and Hodgkin lymphoma: case report and review of the literature in immunocompromised hosts.

    Lupia T, Crisà E, Sangiorgio V, et al.

    Le infezioni in medicina 2024; (32(1)):103-112 doi:10.53854/liim-3201-14.

    PMID: 38456027
  15. 15

    Imaging of Eosinophilic Lung Diseases.

    Price M, Gilman MD, Carter BW, et al.

    Radiologic clinics of North America 2016; (54(6)):1151-1164 doi:10.1016/j.rcl.2016.05.008.

    PMID: 27719981
  16. 16

    Measurement of the IgG Avidity Index in the Diagnosis of Clinical Toxocariasis Patients.

    Menu E, Kopec L, Luciani L, et al.

    Pathogens (Basel, Switzerland) 2021; (10(9)) doi:10.3390/pathogens10091086.

    PMID: 34578119

This page explains toxocariasis diagnostic testing for educational purposes. Always consult your pediatrician or infectious disease specialist to interpret your child's specific lab and imaging results.

Get notified when new evidence is published on Toxocariasis.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.