Failure to induce resistance of Schistosoma japonicum to praziquantel.

In order to explore the possible occurrence of inducing resistance of Schistosoma japonicum to praziquantel (PZQ), a set of animal experiments were carried out. Outbred mice (NIH strain), Anhui isolates of S. japonicum and Oncomelania hupensis were used. In one protocol five weeks after being infected with 48-52 cercariae, mice were orally dosed with PZQ 300 mg/kg, and killed 82 days later to isolate eggs from the liver. Snails were exposed to miracidia released from egg-hatching. F1 progeny were thus obtained through cercarial inoculation. The same scheme was applied for the establishment of the F2 generation. In another protocol two weeks after infection, PZQ 50 mg/kg/day was given to mice for 5 days. Eggs were collected 26-27 days post treatment and the identical procedures were adopted for F1 and F2 generations successively. Analysis of total worm and female worm reduction rates indicated that there was no significant difference between the sensitivity to PZQ of F1 and F2 progenies of S. japonicum and the parent worms.