Casoni skin test
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echinococcosis AND diagnosis
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WHO echinococcosis diagnosis serology imaging hydatid disease
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Casoni skin test is an old intradermal hypersensitivity test for diagnosing hydatid disease caused by Echinococcus granulosus.
- Principle: detects immediate allergic reaction to hydatid cyst fluid antigen.
- Method: a small amount of sterile hydatid fluid antigen is injected intradermally.
- Positive result: local wheal, erythema, and itching within about 15-30 minutes. A delayed reaction may also occur.
- Interpretation: suggests prior sensitization to hydatid antigen, but is not diagnostic by itself.
- Limitations: low specificity, false positives with other parasitic infections and false negatives in some hydatid cases. There is also a small risk of allergic reaction.
- Current role: largely obsolete and not recommended as a routine diagnostic test. Diagnosis now relies on ultrasonography/CT/MRI plus specific serology, commonly ELISA or immunoblot.
The medical text notes that Casoni testing “often lacks specificity” (Park's Textbook of Preventive and Social Medicine, p. 563-575). WHO states that cystic echinococcosis is diagnosed by imaging, with serology used for laboratory confirmation, and the CDC diagnostic guidance similarly supports imaging with serologic tests.
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