Immunologic diagnosis of schistosomiasis: II. Further studies on the sensitivity and specificity of delayed intradermal reactions *

Abstract

The specificity of the delayed intradermal reaction was compared to that of the immediate response in 80 adult St. Lucians with proven schistosomiasis mansoni, using homologous and heterologous antigens. Adult worm antigens at a uniform concentration of 35 \g=m\g/ml from four geographic strains of Schistosoma mansoni (St. Lucian, Puerto Rican, Brazilian, and Egyptian) and from S. haematobium and S. japonicum were color coded and injected randomly in the skin of the upper back. The immediate reactions to all the antigens showed equal sensitivity (94 to 99% positive). The delayed reactions with the four S. mansoni strains ranged from 49 to 60% positivity, but the heterologous S. haematobium and S. japonicum antigens were significantly less sensitive, with only 20% and 30% positive reactions. In an attempt to improve the sensitivity of the delayed intradermal test, 30 of the 80 St. Lucians were retested 1 month later with different concentrations of the Puerto Rican antigen (5, 15, 35, 70 \g=m\g/ml). Immediate reactions were 100% at all but the lowest concentration (93%). Delayed reactions were at their peak (87%) at the standard concentration of antigen (35 \g=m\g/ml), the other concentrations being similar with the exception of the lowest (53%). Comparison of the results of the two series of tests performed 1 month apart in the same individuals revealed no changes in the immediate reactions, but a marked increase in both the percentage positivity and the mean lesion area in the delayed response.