Abstract: Objective To investigate the effects of Schistosoma japonicum (S.japonicum )infection on the survival rate and the antioxidant enzyme system of Oncomelania hupensis(O.hupensis).Methods O.hupensis snails were infected with ten-fold S.japonicum miracidium in laboratory setting (experimental group),and snails without miracidium infection were included as controls.Three replicates were performed for each treatment.The deaths of O.hupensis were continuously recorded till the 15th week following infection,and the activities of superoxide dismutase (SOD),catalase (CAT) and peroxidase (POD) as well as malondialdehyde (MDA) in the snail were measured at time points of 0,6,12,24 and 48,72 h and week 1,2,4,6,8 and 12,respectively.Results After infection,the weekly mortality of O.hupensis was significantly higher in experimental group than in control group,and the cumulative mortality was 43.6% in the experimental group and 5.93% in the control group by week 15.The activities of antioxidative enzymes initially rose,followed by a reduction in O.hupensis snails.SOD activity appeared higher in the experimental group at 24 h compared to the control group(P <0.05),peaked at week 4 and became parallel with levels in control group by week 6.The activity of CAT and POD in experimental group was significantly different from that of the control group at 72 h (both P <0.01),and peaked at week 1 and week 2,respectively,then arrived at normal level.However,MDA content in the infected O.hupensis snails continued to increase,and was statistically different from that of the un-infected controls since week 2 (P <0.01).Conclusion The infection of S.japonicum can induce oxidative stress in O.hupensis,and the O.hupensis could handle the stress by increasing the activities of antioxidative enzymes at early stage.Nevertheless,oxidative damage would occur in O.hupensis over time once the oxidative stress gradually overwhelmed the regulative capability of O.hupensis itself,eventually leading to the death of O.hupensis snails.

Key words: Oncomelania hupensis, Infection , Antioxidant enzyme system , Malondialdehyde