Praziquantel treatment against Cardicola blood flukes: Determination of the minimal effective dose and pharmacokinetics in juvenile Pacific bluefin tuna

摘要

Blood flukes of the genus Cardicola cause significant problems in the bluefin tuna farming around the world. In Japan, the mortality of the juvenile Pacific bluefin tuna Thunnus orientalis (PBT) caused by C. orientalis and C. opisthorchis has become a serious issue in the tuna farming industry in recent years. Oral treatment with praziquantel (PZQ) is highly effective against blood flukes and is indispensable for sustainable tuna farming. To develop a proper and safe drug treatment procedure, we investigated the minimum effective dose and pharmacokinetics of PZQ in juvenile PBT. Juvenile tuna were orally administered various doses of PZQ (0, 3.75, 7.5, 15 and 30 mg/kg body weight (BW)) once a day for 3 consecutive days, and the occurrence of C. opisthorchis before and after the treatment was compared. A significant decrease in the number of flukes was observed in the 3.75 mg/kg group, and complete eradication of flukes was achieved at dosages of 7.5 mg/kg and greater. This result indicates that the minimal effective dose of PZQ for treating C. opisthorchis is between 3.75 and 7.5 mg/kg, which is less than 1/20 of the treatment dose used for treating the skin fluke Benedenia seriolae in yellowtail culture. We used high-performance liquid chromatography analysis to assess the temporal changes in the concentrations of PZQ in serum, muscle, the liver and the kidney after a single administration of PZQ at 15 mg/kg BW. The PZQ concentration in the tissues peaked between 0.5 and 1.5 h following administration, and PZQ was undetectable after 24 h. The highest serum concentration was 2.0 mu g/mL, which is likely to be the lethal dose for C. opisthorchis. These results suggest that PZQ treatment is a highly effective and relatively safe method to control blood flukes in the tuna farming industry