Abstract
Cyprinid herpesvirus 3 (Cy HV ‐3) or koi herpesvirus ( KHV ) is a virulent viral infection in common carp and koi. The disease has caused global epizootic and economic loss in fish aquaculture and in the wild. Clinacanthus nutans (Burm. f.) Lindau is a well‐known medicinal plant used in Thai traditional medicine. Virucidal effects of the plant extract against human herpes simplex virus have been reported. In this study, C. nutans crude extract was tested for antiviral activities against Cy HV ‐3 in koi carp. Results showed effective antiviral activity against Cy HV ‐3 pre‐ and post‐infection. The 50% lethal concentration ( LC 50 ) of extract was higher than 5 mg/ml. The 50% effective dose ( ED 50 ) was 0.99 mg/ml, 0.78 mg/ml, 0.75 mg/ml and 0.71 mg/ml at 1, 2, 3 and 4 hr pre‐infection, respectively. The ED 50 from post‐infection tests was 2.05 mg/ml and 2.34 mg/ml at 0 and 24 hr, respectively. These results demonstrated that crude extract expressed antiviral activity against Cy HV ‐3 and can be applied as a therapeutic agent in common carp and koi aquaculture.