Up-converting phosphor technology-based lateral flow assay for detection of Schistosoma circulating anodic antigen in serum

Abstract

Schistosoma sp. circular anodic antigen (CAA) serum concentrations reflect actual worm burden in a patient and are a valuable tool for population screening and epidemiological research. However, for the diagnosis of individual imported schistosomiasis cases, the current enzyme-linked immunosorbent assay (ELISA) lacks sensitivity and robustness. Therefore, a lateral flow (LF) assay was developed to test CAA in serum for individual diagnosis of imported active schistosome infections. Application of fluorescent submicron-sized up-converting phosphor technology (UPT) reporter particles increased analytical sensitivity compared to that of the standard ELISA method. Evaluation of the UPT-LF test with a selection of 40 characterized epidemiologic samples indicated a good correlation between signal intensity and infection intensity. Subsequently, the UPT-LF assay was applied to 166 serum samples of Dutch residents (immigrants and travelers) suspected of schistosomiasis, a case in which group routine antibody detection frequently fails straightforward diagnosis. The UPT-LF assay identified 36 CAA-positive samples, compared to 15 detected by CAA-ELISA. In conclusion, the UPT-LF assay is a low-complexity test with higher sensitivity than the CAA-ELISA, well suited for laboratory diagnosis of individual active Schistosoma infections.

FIG. 1.

Illustration of the UPT-LF CAA test strip and UPT-LF CAA assay. The immunoassay was performed in microtiter plate wells. After binding of the antigen to the CAA-specific UPT reporter, lateral flow was initiated by placing LF strips in the microtiter plate wells. The LF strips have a width of 4 mm and a total length of 7.8 cm and contain a CAA-specific test line and a UPT control line. Upon completion of the flow, the LF strips were interrogated with infrared light, revealing the deposition of the UPT reporter along the strip. Examples of scans obtained with positive and negative UPT test line signals are shown.

FIG. 2.

Analytical sensitivity of the UPT-LF assay. (A) Comparison of UPT-LF with ELISA. (B) LOD of UPT-LF and indication of positive cutoff threshold (UPT-LF value of 0.081) and negative cutoff threshold (UPT-LF value of 0.053) for CAA detection in serum TCA extracts.

FIG. 3.

Evaluation of the UPT-LF CAA assay. Low, moderate, high, and controls each represent a set of 10 defined serum samples from different areas of schistosomiasis endemicity. Antibody negatives (n = 43) and antibody positives (n = 123) represent a selection of 166 collected serum samples of suspected imported cases.