Early detection of circulating DNA of Schistosoma japonicum in sentinel mice models.

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.

DNA detection of Schistosoma japonicum: diagnostic validity of a LAMP assay for low-intensity infection and effects of chemotherapy in humans.

BACKGROUND: Schistosomiasis has decreased significantly in prevalence and intensity of infection in China, thus more accurate and sensitive methods are desperately needed for the further control of schistosomiasis. The present work aimed to assess the utility of the loop-mediated isothermal amplification (LAMP) for detection of light intensity infection or false-negative patients and patients post-treatment, targeting the highly repetitive retrotransposon SjR2 of Schistosoma japonicum. METHODOLOGY/ PRINCIPAL FINDINGS: LAMP was first assessed in rabbits with low intensity infection (EPG<10). Then 110 patient sera from Hunan Province, China, and 47 sera after treatment by praziquantel were used to evaluate the diagnostic validity of LAMP. Meanwhile, 42 sera from healthy individuals in a non-endemic area, and 60 sera from "healthy" residents who were identified as being negative for feces examination and immuno-methods in an endemic area were also examined. The results showed that LAMP could detect S. japonicum DNA in sera from rabbits at 3rd day post-infection. Following administration of praziquantel, the S. japonicum DNA in rabbit sera became negative at 10 weeks post-treatment. Of 110 sera from patients, LAMP showed 95.5% sensitivity, and even for 41 patients with less than 10 EPG, the sensitivity of LAMP still reached to 95.1%. For 47 patients after treatment, the negative conversion rate of S. japonicum DNA in patient sera increased from 23.4%, 61.7% to 83.0% at 3 months, 6 months and 9 months post-treatment, respectively. No false-positive result was obtained for 42 human sera from non-endemic area, while for the 60 "healthy" individuals from endemic area, 10 (16.7%) individuals were positive by LAMP, which suggested that these individuals might be false-negative patients. CONCLUSIONS/ SIGNIFICANCE: The present study demonstrated that the LAMP assay is sensitive, specific, and affordable, which would help reduce schistosomiasis transmission through targeted treatment of individuals, particularly for those with negative stool examinations who may yet remain infected. The LAMP assay may provide a potential tool to support schistosomiasis control and elimination strategies.