Antiviral activity of several Thai traditional herb extracts against fish pathogenic viruses

Extracts from 18 Thai traditional herbs were prepared by boiling with ethanol under a soxhlet apparatus and virucidal activity against fish pathogenic viruses (IHNV, OMV and IPNV) was tested by plaque reduction method using CHSE-214 cells. When the viruses were exposed to herb extract at 500 mu g/ml before inoculation to CHSE-214 cells, all herbs showed antiviral activity against IHNV and OMV, reducing plaques by 65-100% and 20-100%, respectively. However, in the case of IPNV, no plaque reduction was observed by any herbs tested. Some kinds of the herb extracts prevented viral infection, when CHSE-214 cells were treated with 100 mu g/ml of herbs for 3 h before viral infection. The percent of plaque reduction above 50% was observed in 6, 8 and 6 kinds of herb extracts for IHNV, OMV and IPNV, respectively. These extracts may inhibit the viral adsorption to the cells. When 100 mu g/ml of the herb extracts was applied for infected cells, the percent of plaque reduction above 50% was observed in 0, 8 and 5 kinds of herb extracts for IHNV, OMV and IPNV, respectively. This means that some of the herb extracts may inhibit the replication of OMV and IPNV in CHSE-214, but no herb has any effect for IHNV infection. Moreover, all of the tested herb extracts showed low toxicity to CHSE-214 cell line, the cytotoxic 50% value being 1,200-41,500 mu g/ml.