Casoni's Test

Intradermal test, used for diagnosis of hydatid cyst disease caused by Echinococccus granulosus (Dog tapeworm). Introduced by Casoni in 1911.

Antigen used – Hydatid fluid collected from animal/human cyst and sterilised by Seitz filtration.

Control – Sterile saline.

Principle of the test – Immediate type of hypersensitivity primarily. Type IV Delayed hypersensitivity also plays a part.

Test – 0.2 ml of antigen injected intradermally on forearm and equal volume of saline injected on the other forearm. Observations made for next 30 mins and after 1 to 2 days.

Positive test –Appearance of wheal within 30 minutes on test forearm about 5 cms in diameter, with multiple pseudopodia like projections, fading in about an hour. There must not be any such a reaction on the control side.

Secondary reaction consisting of oedema and induration (Type IV – Tuberculin type Delayed type of hypersensitivity) after 8 hrs.

The test is very sensitive, but not specific. False positive reactions known to occur in other related parasitic infections.

Precaution – Being a type I hypersensitivity reaction, anaphylactic reaction tray must be kept ready before carrying out the test.