Protective efficacy of Clinacanthus nutans on yellow-head disease in black tiger shrimp (Penaeus monodon)

The leaves of Clinacanthus nutans Lindua, a well-known Thai traditional medicine against viral disease in human being, were used to extract antiviral substances by ethanol using soxhlet apparatus. The extract was tested for its activity against yellow-head rhabdovirus (YRV) in black tiger shrimp (Penaeus monodon). Virucidal effect was investigated by observation of mortality of the shrimp injected with the extract-treated virus. The results showed that extract of C. nutans inhibited YRV in vitro with the minimum concentration of 1 mu g/ml. Protective efficacy of the extract on YRV infection in shrimp was tested by oral administration of the extract mixed pellet. As the result, the protective efficacies obtained were 44.6, 57.4 and 4.2% in the shrimp groups fed the extract at 0.1, 1 and 10 g/kg pellet, respectively, indicating that the C. nutans extract mixed with pellet at 1 g/kg could most effectively control YRV infection in shrimp.