Immunochromatographic Test Evaluated to Diagnose Schistosomiasis

Volunteers were classified into three infection status groups based on duplicate Kato-Katz thick smears from one stool sample (2KK test): 41 negative individuals from non-endemic areas, 41 negative individuals from endemic areas and 48 infected individuals from endemic areas.

The rapid immuno-chromatographic test used was the commercially available Bilharzia RDT (Rapid Medical Diagnostics; Pretoria, Republic of South Africa), which measures a parasite-derived “circulating cathodic antigen (CCA)” in the urine of patients infected with S. mansoni. Infection status was also determined by the CCA-ICT and infection exposure by antibody enzyme-linked immunosorbent assay (ELISA) to S. mansoni soluble egg antigen (SEA) and soluble (adult) worm antigen preparation (SWAP).

The investigators found that sensitivity and specificity were influenced by whether the trace score visually adjudicated in the CCA-ICT was characterized as positive or negative for S. mansoni infection. When the trace score was interpreted as a positive rather than as a negative result, the specificity decreased from 97.6% to 78.0% whereas sensitivity increased from 68.7% to 85.4%. A significantly positive correlation between the CCA-ICT scores and egg counts was identified. Considering 2KK as reference test, the discriminating power of the CCA-ICT was greater than the SEA-ELISA and SWAP-ELISA.

The authors concluded that the performance of the CCA-ICT in the Brazilian communities endemic for schistosomiasis mansoni support those from Africa in areas with greater infection prevalence and intensities, the CCA-ICT may be useful as a tool to indicate community-based preventative chemotherapy without individual diagnosis. However, because of the Brazilian Ministry of Health’s recommendation for individual diagnosis in areas where prevalence is less than 15%, in those areas in which infection intensities are likely to be lowest, the CCA-ICT lacks the sensitivity to be used as standalone diagnostic tool. The study was published on January 11, 2016, in the journal Public Library of Science Neglected Tropical Diseases.

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