Abstract: 　Objective] To study the synergic effect of praziquantel(PZQ) and host acquired immunity on Clonorchis sinensis. [Methods] Acquired immunity to C.sinensis was induced by immunization with crude adult worm antigen (AW Ag) and excretory-secretory antigen (ES Ag) or infection with C.sinensis metacercariae. The effect was assessed by the worm reduction rate compared with the control groups after challenge infection with 50 metacercariae and treated orally with a subcurative dose of praziquantel (50 mg/kg). Significant test was performed by analysis of variance (ANOVA) and Npar1 way Kruskal-Wallis test. All calculations were performed by PC-SAS system. [Results] 1. PZQ was more effective against C.sinensis larvae than against adult worms in the control (P<0.001), ES Ag (P<0.01) or crude AW Ag immunization group (P<0.001). 2. As compared with the control, the worm reduction rate after challenge infection was significantly higher (P<0.001) in ES Ag immunized group(35.6%) and metacercaria infection group(97.5%) and less in crude AW Ag group(23.4%). The PZQ efficacy was significantly enhanced in ES Ag immunized group. [Conclusion] The efficacy of PZQ against C.sinensis could be synergically enhanced in rats by inducing host acquired immunity. \;

Key words: Clonorchis sinensis, praziquantel, chemotherapeutic efficacy, protective immunity, immunization.