Studies on the Standardization of the Intradermal Test for the Diagnosis of Bilharziasis

Abstract

Summary Intradermal tests conducted in Brazil were made with antigens prepared in the United States from schistosome material collected in Puerto Rico and with antigens obtained and prepared in Brazil. No significant difference in activity was noted when the nitrogen content of the antigens was adjusted to the same levels. Tests indicate that the skin test is not very sensitive in detecting infections in children below 5 years of age, that girls are less reactive than boys, and women less reactive than men. Tests were performed on both the arm and the back and the back was found to be the more sensitive site for skin testing. Women and girls were skin tested in the scapular region near the neck above the dressline. Reactions on the back in women are equal to those on the arm in men. Adult males can be tested on the arm but for maximum sensitivity all other individuals should be tested on the back. A dose of 0.05 ml of antigen containing 20 to 40 µg N/ml, injected intracutaneously with a 27-gauge needle, is recommended. The test is read after 15 minutes by measuring the area of the wheal. Areas of 1.0 cm2 or greater are considered positive tests. The antigen recommended is an adult worm extract. Further research is needed to eliminate nonspecific reactions of the antigen in the skin of normal individuals.