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Currently in China, the schistosomiasis control program has shifted its focus from transmission control to the elimination of the disease. Effective forecast and surveillance systems of schistiosomiasis are of great importance for issuing timely and early warnings on risk of infection, and therefore implementing preventive measures to avoid infection. There is great demand in more sensitive and specific methods to improve the surveillance system for early detection of S. japonicum infection in sentinel mice. In this study, we reported a sensitive nested-PCR assay targeting a 303-bp fragment from highly repetitive retrotransposon SjCHGCS19 to detect the S. japonicum DNA in sera of experimental mice. Meanwhile, detection efficacy of the nested-PCR was compared with two conventional methods for field monitoring schistosomiasis such as ELISA and IHA. The nested-PCR assay could detect the specific DNA at 3-day post-infection in sera of mice with 5 cercariae infection, while for ELISA and IHA, both show negative results even after 2 weeks post-infection in mice with 20 cercariae infection. Our results demonstrated the DNA-based assay was more sensitive to make early diagnosis of S. japonicum infection in sentinel mice models, which will improve the early-warning ability of schistosomiasis surveillance system.

A specific PCR assay for the detection of Schistosoma japonicum DNA in rabbit fecal and serum samples was developed by amplifying a 230-bp fragment from the sequence information of the clone G55A of the highly repetitive retrotransposon SjR2. The minimum amount of DNA detectable using the PCR assay was 0.8pg, and the expected PCR product was amplified when DNA equivalent of 1.1 egg from feces was used as template. In the meantime, serum anti-worm IgG was examined by ELISA. ELISA gave positive results at 4-6 weeks post-infection depending on the cercarial doses. The parasite eggs were detected in feces at 7 weeks post-infection. In contrast, S. japonicum DNA was detected in sera at first week post-infection, and it became negative at 10 weeks post-treatment, whereas the anti-worm IgG was still at high levels at 23 weeks post-treatment. These data demonstrated that the PCR assay established provides a potential tool for the early diagnosis and therapy evaluation for S. japonicum infection in humans.