Schistosomiasis Japonica in Barrio San Antonio, Basey, Samar, in the Philippines

V. The Enzyme-linked Immunosorbent Assay (ELISA) Compared with Quantitative Stool Examination and the Circumoval Precipitin (COP) Test

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  • The University of Chicago, Department of Microbiology, The Philippine Ministry of Health, Schistosomiasis Research and Control Project, 920 East 58th Street, Chicago, Illinois 60637, Philippines

An enzyme-linked immunosorbent assay (ELISA) utilizing a crude antigen from lyophilized Schistosoma japonicum eggs was developed and used as a serodiagnostic test for schistosomiasis japonica. A total of 338 sera from residents and 268 plasma from grade school children of the endemic barrio of San Antonio, Basey, Samar in the Philippines were tested and results were compared with our previous findings by a quantitative stool examination (MFCT) and the circumoval precipitin test (COPT) done with whole serum. “Normal” sera from Filipinos who had never been to schistosomiasis-endemic areas were also tested, as were human sera from a variety of cases of other helminthiases. A negative serum pool and known positive controls were included in each test plate to delimit positive absorbance values and to check and adjust reagent activities. None of the “normal” sera was ELISA-positive; sera from human cases of trichinosis and schistosomiasis mansoni and haematobia showed crossreactivity, but these helminthiases are not found in the Philippines. No cross-reactivity was found with sera from human cases of capillariasis philippinensis, filariasis bancrofti, fascioliasis, clonorchiasis, paragonimiasis, cysticercosis, and echinococcosis. Among the barrio residents, significantly more positives were found by ELISA at serum dilution 1:16 (90.2%) than were found by COPT (65.1%) or MFCT (59.2%). All but one of 200 residents (99.5%) with parasitologically verified S. japonicum infections were ELISA-positive; all 220 COPT-positive sera (100.0%) were ELISA-positive. Of 138 stool-negative residents, 76.8% were ELISA-positive; of 118 residents with COPT-negative sera, 72.0% were ELISA-positive. Of the plasma from 268 school children significantly more positives were found by ELISA at dilution 1:16 (60.1%) than by COPT using undiluted plasma (35.8%). All (100%) COPT-positive plasma were ELISA-positive; of 172 COPT-negative plasma, 37.8% were ELISA-positive. Our findings support the conclusion that ELISA sensitivity is excellent and that the technic detects S. japonicum infections which would remain cryptic if only a single stool examination and/or COPT were used for diagnosis. All but one of 44 residents with a history of stibophen chemotherapy were ELISA-positive. Our findings suggest that 90% of Barrio San Antonio residents and 60% of children attending the barrio elementary school are currently infected with S. japonicum.