Urine Circulating Anodic Antigen Test Diagnoses Schistosomiasis

An accurate diagnosis is essential and should be adapted to the specific stage of a schistosomiasis control program and parasitological methods to detect Schistosoma eggs in stool are widely used.

These conventional parasitological methods are insensitive for the detection of light-intensity infections and techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings and verification of elimination.

An international team of scientists led by those at the Swiss Tropical and Public Health Institute (Basel, Switzerland) collected a total of 1,740 urine samples in 2013 from children on Pemba Island (Tanzania). The children attended schools where the S. haematobium prevalence was less than 2%, 2% to 5%, and 5% to 10%, based on a single urine filtration. On the day of collection, all samples were tested for microhematuria with reagent strips and for the presence of S. haematobium eggs with microscopy.

The team determined the accuracy of a urine-based up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay on 1,200 samples eight months later, while urine filtration slides were subjected to quality control (QCUF). In the absence of a true “gold” standard, the diagnostic performance was calculated using latent class analyses (LCA). The UCP-LF CAA designated UCAA2000 is currently considered to show the best trade-off between a high sensitivity and convenient field applicability.

The “empirical” S. haematobium prevalence revealed by UCP-LF CAA, QCUF, and reagent strips was 14%, 5%, and 4%, respectively. LCA revealed a sensitivity of the UCP-LF CAA, QCUF, and reagent strips of 97%, 86%, and 67% respectively. Test specificities were consistently above 90%. Since QCUF revealed more S. haematobium-infected individuals than the initial urine filtration microscopy, only QCUF results were considered for the calculation of sensitivity and specificity. There was a significant relationship between circulating anodic antigen CAA pg/mL levels and S. haematobium egg counts, between CAA pg/mL levels and microhematuria grading, and between egg counts and microhematuria grading.

The authors concluded that the UCAA2000 as a suitable tool for large-scale monitoring of urogenital schistosomiasis in control programs in low-endemicity settings targeting elimination and for surveillance in areas that achieved elimination. For surveillance at a smaller scale, including testing of suspected cases in remote public health care centers without laboratory equipment, a simple-to-use but still highly sensitive point-of-care-CAA rapid test is highly desirable. The study was published on May 14, 2015, in the journal Public Library of Science Neglected Tropical Diseases.

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Swiss Tropical and Public Health Institute