Antiparasitic effects of Sophora flavescens root extracts on the ciliate, Cryptocaryon irritans

Abstract The antiparasitic effects of 59 water- and methanol-soluble herbal extracts were screened for their potential to inhibit cilia-based motility of the protozoan, Cryptocaryon irritans , during its infective (theront) phase. Both the water- and methanol-soluble extracts of five herbs had strong antiparasitic activity. In vitro results were confirmed in vivo in oral-challenge trials with the red sea bream, Pagrus major . The water-soluble Sophora flavescens extract had the most potent anti- C. irritans activity. For a short-term oral-challenge trial, the number of parasites in the groups treated with 5 or 10 g·kg − 1 feed of S. flavescens water-soluble extract was significantly lower than that in the control group and the group treated with 10 g·kg − 1 feed reduced the number of parasites by more than 40% compared with the control. In an 80 day oral challenge trial with P. major , all the fish in the group that were treated with the extract (5 g·kg − 1 feed) survived throughout the experimental period, which contrasts with the 100% mortality seen in the control group. Furthermore, the anti- C. irritans effect of the extract in previously infected P. major was also evaluated in a 4 day oral-challenge trial. In this trial, the number of parasites in the group treated with the extract (5 g·kg − 1 feed) was reduced by 30% compared with the control group. These results suggest that the water-soluble S. flavescens extract could be effective for controlling C. irritans infections.