Abstract:
Cyprinid herpesvirus 3 (CyHV-3) or Koi herpesvirus (KHV) is a virulence 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, dichloromethane fraction and n-butanol fraction were tested for antiviral activities against CyHV-3 in koi fin cell line. The 50% cytotoxic concentration of crude extract was at 1,701.57 µg/ml, dichloromethane fraction at 522.47 µg/ml and n-butanol fraction at 1,797.98 µg/ml. Effective concentrations of the crude extract pre and post-infection were at 250, 500 and 1,000 µg/ml. The dichloromethane fraction and n-butanol fraction did not have antiviral activity. The C. nutans crude extract was chosen to perform antiviral activity test in koi carp. The results showed effective antiviral activity against CyHV-3 pre and post infection. The 50% lethal concentration of extract was higher than 5,000 µg/ml. The 50% effective doses (ED50) were 991.59 µg/ml, 782.72 µg/ml, 749.05 µg/ml and 707.80 µg/ml at 1, 2, 3 and 4 hours pre-infection, respectively. The ED50 from post infection test were 2,050.88 µg/ml and 2,337.74 µg/ml at 0 and 24 hours, respectively. The results showed that crude extract expressed antiviral activity against CyHV-3 can be applied as therapeutic agent in common carp and koi aquacultures.
