Immunodiagnosis of schistosomiasis mansoni in a low endemic area in Surinam by determination of the circulating antigens CAA and CCA.

We evaluated the applicability of circulating antigen detection in serum and urine for the diagnosis of Schistosoma infections in a low endemic area. In total 389 individuals from Saramacca (Surinam) participated in the survey. Stool samples were examined using the Kato method, while circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were determined by highly specific monoclonal antibody-based ELISA's. Also schistosome specific IgM antibodies were measured by the indirect immunofluorescence assay, but the diagnostic performance of this test was found to be poor in this population. S. mansoni eggs were found in 29% of the examined cases, while CAA and CCA could be demonstrated in 23% and 17% of the serum samples and in 3% and 28% of the urine samples, respectively. Forty three percent of the study population was positive in at least one of these diagnostic assays, indicating that each individual test misses a substantial part of the subjects with an active infection. In most positive cases, intensities of infection were very low. As 204 individuals participated in all screening assays, diagnostic performance of each test was evaluated in this sub-population. The highest sensitivities were achieved with the urine-CCA assay and the parasitological examination, detecting 59 and 58 out of the 107 cases with an active infection, respectively. The serum-CAA assay detected 47 positive cases. Our results demonstrate that determination of circulating antigens, especially CCA in urine and CAA in serum, provides information additional to the parasitological examination, for the assessment of prevalence and intensity of Schistosoma infection in low endemic areas.

A sedimentation-selective filtration method for the diagnosis of light infections with Schistosoma mansoni.

An epidemiological survey for infection with Schistosoma mansoni was carried out in the community of Catharina Sophia in northern Surinam. The merits of a more sensitive diagnostic system, the Sedimentation-Selective-Sieving (SSF) method, were evaluated; the results were compared with those obtained with the standard Kato-Katz thick smear technique. Examination of a duplicate Kato smear (2 x 25 mg) resulted in a prevalence of 22% while the real prevalence was shown to be more than 42%. The SSF procedure was shown to have a comparatively high sensitivity although the egg counts per gram (calculated on the basis of examining samples of 2-3 g) were considerably lower than those derived from Kato smears. The implications for epidemiological surveillance of communities with excretion of low numbers of S. mansoni eggs are discussed and the observations are compared with those one might expect on the basis of mathematical modelling (De Vlas et al., 1992).