Development of a latex microsphere-based lateral flow immunoassay for the diagnosis of schistosomiasis japonica

Abstract

Background: Zoonotic schistosomiasis, caused by Schistosoma japonicum, remains prevalent in China, the Philippines and small foci of Indonesia. Rapid point-of-care (POC) diagnostic tools are attractive and promising tools for evaluating the efficacy of intervention strategies against schistosomiasis. Methodology: The diagnostic potential for five recombinant antigens was tested by enzyme-linked immunosorbent assay (ELISA) using sera from individuals with a positive Kato-Katz (KK) result for S. japonicum (n=28) and non-endemic controls (n=12). A latex microsphere (LM)-based lateral flow immunoassay (LFIA) incorporating the recombinant SjSAP4 (rSjSAP4) antigen was developed for the diagnosis of schistosomiasis japonica. The testing conditions including diluent, dilution factor, and reaction time, were optimised for the developed LFIA. Under the optimised conditions, serum samples from individuals living in an S. japonicum endemic area (n=549) and non-endemic controls (n=50) were tested with the established LFIA cassettes. Results were imaged by a smartphone and analyzed by the ImageJ program. An R-value, which was the intensity ratio of the test line vs. control line, was calculated for each strip, converting the results into quantitative data. Main findings: ELISA assays confirmed that the SjSAP4 was the optimal candidate for serological diagnosis of schistosomiasis japonica. Under the optimised testing conditions, the LM-based LFIA strips showed a sensitivity of 80.6% and a specificity of 98.0% at a cut-off R-value of 0.1031. Meanwhile, the developed LFIA showed a significant positive correlation with the rSjSAP4-ELISA assay (r=0.8269, 95% CI, 0.8127-0.9446; p<0.0001). The schistosomiasis prevalence determined by the LFIA strips was about 1.8 times higher than that obtained with the 6-slide KK procedure. Conclusions/Significance: The study indicated that the LFIA assay established here represents a POC diagnostic tool that is suitable for on-site screening of human S. japonicum infection, using minimal equipment and adhering to the ASSURED criteria for POCs from the WHO.