The soluble worm antigens-specific antibodies used as biomarkers of Schistosoma japonicum in a low prevalence and intensity endemic area of Hubei, China

The precise diagnosis of Schistosoma japonicum (S. japonicum) infection plays a critical role in achieving the ultimate goal of eliminating schistosomiasis in endemic regions. We evaluated the S. japonicum soluble worm antigen protein (SWAP) specific-IgG, IgG₄ and IgE levels, and evaluated the association between S. japonicum infection and these antibodies in a sample of 837 residents from a S. japonicum-endemic area in Hubei province, China. The anticipants were divided into the Training Set (TS) and Validation Set (VS) based on the chronological order. Enzyme-linked immunosorbent assays were performed to detect the SWAP-specific antibodies. Three algorithms for identifying S. japonicum infection were generated in the TS and subsequently validated in the VS. The findings were further replicated in an independent cohort from an endemic area for Schistosoma mansoni (S. mansoni) in Brazil. Our results indicated for the first time that S. japonicum-infected individuals had higher levels of SWAP-specific IgG, IgG₄ and IgE, and lower value of the IgE/IgG₄ ratio than uninfected individuals in both the two sets (p < 0.01). Both the infected and uninfected individuals had a high prevalence of seropositivity for IgG. We further showed that the predictive model EGR (IgE/IgG₄ ratio) score performed best in Chinese population (area under the receiver operating characteristic (AUROC) 0.905, sensitivity 82.7%, specificity 84.0% in the TS; AUROC 0.933, sensitivity 87.7%, specificity 89.1% in the VS). Nevertheless, the predictive model IgG₄ score performed best in Brazilian cohort (AUROC 0.788, sensitivity 73.2%, specificity 73.3%). In summary, SWAP-specific IgG could be used as a biomarker for identifying individuals who have been previously exposed to S. japonicum, and furthermore the SWAP-specific IgE/IgG₄ could be used as an immune biomarker for S. japonicum infection in particular in the endemic areas with low prevalence and intensity.