IMMUNODIAGNOSIS OF INFECTION WITH SCHISTOSOMA-MANSONI - COMPARISON OF ELISA, RADIOIMMUNOASSAY, AND PRECIPITATION TESTS PERFORMED WITH ANTIGENS FROM EGGS

In the first part of this study we found that the circumoval precipitin (COP) test with fresh whole eggs of Schistosoma mansoni was more sensitive and specific than other test with cercariae or adult worms, or their extracts, as antigens. In this study we evaluated more current serologic tests in which eggs, or soluble extracts of eggs, were used as antigens. Serum samples from 121 individuals who participated in a longitudinal population-based study of schistosomiasis in Parcelas de Boqueron, Puerto Rico, were used in this study. All serum samples were tested blindly for antibodies to S.mansoni by the various serologic tests. Infection with S. mansoni was determined by examining a series of fecal samples (3-6) by the modified Ritchie formol-ether concentration technique. Both the radioimmunoassay with MSA1 as antigen and the COP test had a diagnostic sensitivity of 95% and detected 100% of the individuals excreting ten or more eggs per gram. The enzyme-linked immunosorbent assay (ELISA) with soluble egg antigen had a sensitivity of only 75%, and the Ouchterlony immunodiffusion with the same antigen, only 41%. Specificity was highest with the COP test, which correctly identified 96% of the uninfected individuals. A rating index we developed was useful in ranking these tests according to their diagnostic strength and was also useful in establishing a criterion of positivity for the ELISA.