Inhibitory effect of essential oils obtained from plants grown in Colombia on yellow fever virus replication in vitro

Background: An antiviral drug is needed for the treatment of patients suffering from yellow fever. Several compounds present in plants can inactive in vitro a wide spectrum of animal viruses. Aim: In the present study the inhibitory effect of essential oils of Lippia alba, Lippia origanoides, Oreganum vulgare and Artemisia vulgaris on yellow fever virus (YFV) replication was investigated. Methods: The cytotoxicity (CC50) on Vero cells was evaluated by the MTT reduction method. The minimum concentration of the essential oil that inhibited virus titer by more than 50% (MIC) was determined by virus yield reduction assay. YFV was incubated 24 h at 4 degrees C with essential oil before adsorption on Vero cell, and viral replication was carried out in the absence or presence of essential oil. Vero cells were exposed to essential oil 24 h at 37 degrees C before the adsorption of untreated-virus. Results: The CC50 values were less than 100 mu g/mL and the MIC values were 3.7 and 11.1 mu g/mL. The CC50/MIC ratio was of 22.9, 26.4, 26.5 and 8.8 for L. alba, L origanoides, O. vulgare and A. vulgaris, respectively. The presence of essential oil in the culture medium enhances the antiviral effect: L. origanoides oil at 11.1 mu g/mLproduced a 100% reduction of virus yield, and the same result was observed with L. alba, O. vulgare and A. vulgaris oils at100 mu g/mL. No reduction of virus yield was observed when Vero cells were treated with essential oil before the adsorption of untreated-virus. Conclusion: The essential oils evaluated in the study showed antiviral activities against YFV. The mode of action seems to be direct virus inactivation.