Detection of echinococosis
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WHO echinococcosis diagnosis ultrasound serology imaging
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Detection of echinococcosis (hydatid disease) relies on compatible imaging plus serology, interpreted with the clinical and exposure history.
1. Clinical suspicion
Consider it in a person from, or with travel to, sheep-raising endemic regions who has:
- Hepatic cyst or mass, often with right upper-quadrant discomfort
- Lung cyst, cough, chest pain, dyspnea, or hemoptysis
- Exposure to dogs, sheep, or contaminated food/water
Many patients are asymptomatic until cysts enlarge or complicate.
2. Imaging: primary diagnostic method
Ultrasound is first line for suspected liver hydatid cysts. Findings include:
- Simple cyst in early disease
- Daughter cysts
- Detached internal membranes, such as the “water-lily” sign
- Hydatid sand
- Partially or fully calcified cyst wall in inactive disease
CT is useful for defining cyst number, calcification, complications, and surgical planning.
MRI is especially useful for biliary involvement, CNS lesions, and better soft-tissue characterization.
For pulmonary disease, chest radiograph and CT may show a well-circumscribed cystic lesion, sometimes with detached membranes after rupture.
3. Serology: supportive, not standalone
Detect antibodies using:
- ELISA for Echinococcus IgG, commonly used screening test
- Immunoblot/Western blot to confirm an equivocal or positive result
Limitations:
- False negatives occur, particularly in lung, brain, bone, or intact inactive cysts.
- Liver cysts are more often seropositive than lung cysts.
- Antibodies can remain positive for years after successful treatment, so serology alone does not prove active infection or cure.
4. Confirming the diagnosis
Diagnosis is usually made by typical imaging plus positive serology in an appropriate epidemiological setting.
Avoid routine diagnostic aspiration or biopsy because puncturing a hydatid cyst may cause fluid leakage, anaphylaxis, and secondary spread. Aspiration is done only as part of a planned specialist procedure, such as PAIR: puncture, aspiration, injection of a scolicidal agent, and re-aspiration.
5. Other tests
- CBC may show eosinophilia, but this is neither sensitive nor specific.
- Liver function tests may become abnormal if there is biliary obstruction or cyst rupture into bile ducts.
- If cystic echinococcosis is uncertain, molecular testing of cyst material can identify the parasite in specialist settings.
Key point: A cyst with daughter cysts or detached membranes on imaging is highly suggestive. A negative blood test does not exclude echinococcosis.
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