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Literature sharing: Rapid RAA assay for Schistosoma haematobium detection — sensitive, specific, and field-ready
Release date:
2026-04-28
Schistosomiasis, a major neglected tropical disease, affects ~258 million people globally, with ~779 million at risk. Over 85% of cases occur in sub-Saharan Africa, where Schistosoma haematobium—the cause of urogenital schistosomiasis—accounts for about two-thirds of infections.
Background
Schistosomiasis, a major neglected tropical disease, affects ~258 million people globally, with ~779 million at risk. Over 85% of cases occur in sub-Saharan Africa, where Schistosoma haematobium—the cause of urogenital schistosomiasis—accounts for about two-thirds of infections. S. haematobium infects the bladder vein and pelvic venous plexus, leading to terminal hematuria, bladder irritation, urinary tract obstruction, renal failure, and even bladder squamous cell carcinoma.
As regular treatment has reduced the prevalence and intensity of S. haematobium infections in endemic areas, low-intensity and asymptomatic infections are increasingly common which are difficult to detect by microscopy or reagent strips; moreover, imported cases persist in non-endemic regions such as China and Europe, where misdiagnosis often occurs due to lack of clinical experience and specialized assays.
Polymerase chain reaction (PCR), real-time fluorescence quantification and LAMP have been used to detect S. haematobium DNA, yet have limitations such as time-consuming and requiring specific equipment. To address these challenges, a recombinase-aided amplification (RAA) based assay was established for the rapid detection of S. haematobium in urine samples.
Results
The cytochrome c oxidase subunit 1 (cox1) gene of S. haematobium was selected as the target gene and primers and probe were designed accordingly. The RAA assay was established using QT BIO’s RAA Nucleic Acid Amplification Kit.
Sensitivity of the RAA assay
The sensitivity of the RAA assay was evaluated using S. haematobium cox1 recombinant plasmid samples at various concentrations (1.0 × 106, 1.0 × 105, 1.0 × 104, 1.0 × 103, 1.0 × 102, and 10 copies/μL). The fluorescence signals increased within 5 minutes for all concentrations tested (Fig. 1A).
Specificity of RAA assay
Cross reactivity test was applied to evaluate the specificity of RAA assay. Increase in fluorescence intensity was only observed for S. haematobium, but not S. japonicum, S. mansoni, Ancylostoma duodenale, Clonorchis sinensis, Echinococcus granulosus, or Ascaris lumbricoides (Fig. 1B).
Performance of RAA assay
9 egg-positive and 48 egg-negative samples were used to test the consistency between RAA assay and traditional microscopy method. The result suggested the consistency was 100% and the positive and negative predictive values were both 100% (Fig. 1C).
Fig. 1 Sensitivity, specificity, and performance of the RAA assay in S. haematobium detection. A. Sensitivity test using S. haematobium cox1 recombinant plasmid at various concentrations. B. Specificity test. C. Evaluation of the RAA assay performance with field-collected urine samples. A total of 57 urine samples were included, 9 were tested positive and 48 were tested negative using microscopy-based egg counting. The fluorescence curves of negative samples were collapsed into one. Figure was adapted from reference.
Discussion
Sensitive and specific diagnostics are critical for schistosomiasis elimination, especially in low-endemic and non-endemic areas with imported cases. Detection of S. haematobium DNA in urine is a highly sensitive indicator of infection. The RAA assay offers a rapid (5–15 minutes), simple, field-deployable alternative to laboratory-based methods, requiring no specialized or expensive equipment. It detected as few as 10 copies/μL of recombinant plasmid, with higher concentrations producing earlier fluorescence signals, suggesting potential for semi-quantitative use. The RAA assay showed no cross-reactivity with S. mansoni, S. japonicum, or other common helminths, confirming high specificity. When validated on 57 field-collected urine samples (9 egg-positive, 48 egg-negative), the RAA assay correctly identified all samples (100% agreement with microscopy, kappa = 1). Although fluorescence signal onset and intensity varied among positive samples, this variability was not related to egg load and was likely due to differences in sample characteristics or DNA degradation during lyophilization, transport, and reconstitution; nevertheless, all positive samples produced strong signals, indicating minimal practical impact. DNA extraction was performed using a low-cost kit ($2.45/sample), and the detected DNA was likely derived from both eggs and cell-free parasite DNA. Compared to LAMP (35–40 min) and traditional methods, RAA is considerably faster, therefore suitable for rapid identification of low-intensity S. haematobium infections. Additionally, the use of lyophilized reagents simplifies sample pretreatment, transport, and long-term storage. Several limitations should be noted, including the small sample size and the lack of cross-reactivity testing against other urinary tract pathogens due to sample constraints. Overall, RAA is a promising tool for rapid, sensitive, and on-site diagnosis of S. haematobium infection, particularly in low-endemic and imported case settings.
Conclusion
The RAA assay is a rapid, sensitive, and field-applicable alternative to conventional diagnostics for S. haematobium infection, particularly valuable in low-endemic and non-endemic areas with imported cases of schistosomiasis.
Reference
Zhao, S. et al. Development and performance of recombinase-aided amplification (RAA) assay for detecting Schistosoma haematobium DNA in urine samples. Heliyon. 9, e23031 (2023).
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