A PCR-based Assay for the Detection of Schistosoma japonicum from Human Samples

Abstract

Background and Objective: Schistosoma japonicum is the causative agent of schistosomiasis in the
Philippines. Current diagnostics suffer from low sensitivity and accuracy, hence an accurate and reliable
diagnosis of schistosomiasis is essential for its prevention and control. In this study, a PCR-based assay for the detection of Schistosoma japonicum for patient stool and serum samples was developed.

Methodology: Three candidate primer sets targeting mitochondrial genes COX3, NAD4, and NAD5 were assessed. COX3 primer pair was used for the rest of the study for sensitivity, specificity, and performance testing. Lastly, the assay using COX3 primer pair was compared to Kato-Katz and circumoval precipitin test (COPT).

Results: COX3 and NAD5 primers showed to be suitable for the assay as sequencing analyses gave high similarities of 96-98% for S. japonicum, while NAD4 showed no similarity to any organisms. The PCR-assay was shown to have a detection limit of 4 ng/ul DNA and is specific only to S. japonicum. The assay detected seven out of ten S. japonicum-spiked stool samples and ten out of ten S. japonicum-spiked serum samples. Comparative performance testing with Kato-Katz and COPT showed high specificity of 100% for both samples, but low sensitivity for formalin-fixed stool samples and stored serum samples.

Conclusion: This study developed a sensitive and specific PCR-based assay to detect S. japonicum from human samples. Our results suggest that this PCR assay could be useful for the detection of S. japonicum in fresh clinical samples and can be further improved to be used as a reference to improve other diagnostic assays for schistosomiasis.