Immediate and delayed-type reactions in caterpillar dermatitis.

The mechanism of dermatitis induced by Euproctis caterpillars has not been fully clarified, although mechanical stimulation by the spicules as well as chemical irritation by venomous components from spicules have been suggested to be involved. In this study, skin tests using venomous spicules and the venomous extract from the caterpillar of E. pseudoconspersa were carried out on a subject. The test site developed both immediate and delayed-type reactions. Next, the crude extract was separated into 8 fractions (No. 1-8) using gel filtration HPLC, and a skin test using each fraction was performed in the same subject. The result showed that only fraction No. 3 caused reactions similar to those in crude venom extract. Then skin tests using the crude venom and fraction No. 3 were performed in 10 healthy volunteers. The skin reaction caused by crude venom was similar to that caused by fraction No. 3 in each subject. Two volunteers showed neither immediate nor delayed-type reactions, 4 volunteers showed a delayed-type reaction, and the other 4 showed both immediate and delayed-type reactions. These results indicate that allergic reactions against venom released by the spicules play a role in the induction of dermatitis by E. pseudoconspersa caterpillars. Variations in the clinical course of individual patients may be attributable to differences in the state of sensitization to the venomous components.