What this test measures
Echinococcus IgG measures antibodies against Echinococcus tapeworm antigens — most commonly E. granulosus (cystic hydatid disease) and sometimes E. multilocularis (alveolar disease). Humans become accidental hosts after ingesting eggs from contaminated food, water, or contact with dogs; the larvae form slow-growing cysts in liver (70%), lung (20%), and occasionally brain, kidney, or bone.
The ELISA-based serology detects IgG raised against echinococcal antigens. Sensitivity is higher for liver cysts than lung cysts, and falls in early or small cysts. Confirmation is by imaging (ultrasound, CT, MRI) and sometimes a Western blot for antigen B subunits.
Why it matters
Cystic hydatid disease is endemic across India, particularly in livestock-rearing states (Maharashtra, Andhra Pradesh, Tamil Nadu, Kashmir, Punjab, North-East), and is one of the leading causes of liver cysts in rural patients. The diagnosis is often suggested by an ultrasound finding (the classic "water lily" sign of a daughter-cyst pattern), and Echinococcus IgG confirms the parasitic aetiology before treatment with albendazole and/or surgery / PAIR (puncture-aspiration-injection-reaspiration).
Treatment decisions hinge on cyst stage (WHO ultrasound classification CE1–CE5), location, and patient factors. Serology is also used post-treatment — antibodies usually persist for months to years after successful treatment but a sustained fall supports cure, while a rising titer suggests relapse or recurrence.
How to prepare
No fasting required. Disclose any recent treatment for hydatid disease — antibody titers can persist for years after successful treatment and rise transiently after cyst rupture, surgery, or PAIR. Disclose travel and rural/agricultural exposure (dogs, sheep, cattle, goats).
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Echinococcus IgG (Index / U/mL)[1][2][3] | Negative (assay-specific) | Negative: low likelihood of active hydatid disease. False-negative possible in early infection, small or calcified cysts, isolated lung disease, or after immunosuppression. If imaging strongly suggests hydatid, repeat in 2–3 months or proceed with imaging-guided diagnosis. | Positive: supports hydatid disease in a patient with compatible imaging. Higher titers correlate with active disease, multiple cysts, or recent cyst rupture. Persistently positive serology after treatment can reflect either ongoing disease or slow antibody decay. |
Hydatid disease — WHO ultrasound cyst stage
| Stage | Appearance | Activity |
|---|---|---|
| CE1 | Anechoic unilocular cyst | Active |
| CE2 | Multivesicular (daughter cysts) | Active |
| CE3a | Detached endocyst (water-lily sign) | Transitional |
| CE3b | Daughter cysts in solid matrix | Transitional |
| CE4 | Heterogeneous, no daughter cysts | Inactive |
| CE5 | Calcified wall | Inactive |
Frequently asked questions
How do people get hydatid disease?
Ingestion of Echinococcus eggs from food, water, or hands contaminated by dog faeces. Dogs are infected after eating organs of infected livestock (sheep, goat, cattle). Rural and pastoral communities are at higher risk.
Does negative serology rule out hydatid?
No. Sensitivity is 60–95% for liver cysts and 50–60% for lung cysts. Small, early, calcified, or pulmonary cysts may not produce a detectable antibody response. Imaging (ultrasound, CT) remains central to diagnosis.
What is the treatment for hydatid disease?
Depends on cyst stage and location. Options include long-course albendazole, PAIR (puncture-aspiration-injection-reaspiration) for active liver cysts, surgical removal for large or complicated cysts, or "watch and wait" for inactive calcified cysts (CE4–CE5).
Can the serology track treatment response?
Partly. Antibody titers usually fall slowly over 1–4 years after successful treatment. A sustained fall supports cure; a rising titer or new high titer suggests relapse. Imaging follow-up is more sensitive than serology alone.
Why does serology stay positive after treatment?
IgG antibodies can persist for years even after successful treatment. Antigen exposure during surgery or PAIR can even transiently raise titers. A persistently positive but stable / falling titer with no imaging change is consistent with cure.
Is hydatid disease common in India?
Yes — particularly in livestock-rearing regions (Maharashtra, Andhra Pradesh, Tamil Nadu, Kashmir, Punjab, North-East). Liver and lung cysts in patients with rural / dog exposure should prompt the diagnosis.
Related Immunology tests
Tests commonly ordered alongside ECHINOCOCCUS - IGG, or that help interpret an unexpected result.
Sources & references
- WHO — Echinococcosis Fact Sheet · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Echinococcosis · accessed 2026-05-30T00:00:00.000Z
- CDC — Parasites: Echinococcosis · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Echinococcus Antibody · accessed 2026-05-30T00:00:00.000Z
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