Antiherpetic activity of the traditionally used complex essential oil Olbas

Essential oils of medicinal plants are increasingly of interest as novel drugs for antiherpetic agents, since herpes simplex virus (HSV) might develop resistance to commonly used antiviral drugs. The antiviral effect of Olbas, a traditionally used complex essential oil, and of cajuput oil, a major constitutent of Olbas, against HSV type 1 was examined. The antiviral activity of these essential oils was tested in vitro on monkey kidney cells using a plaque reduction assay. The 50% inhibitory concentration (IC50) of Olbas and cajuput oil for herpes simplex virus plaque formation was determined at 1.8 microg/ml and 7.5 microg/ml, respectively. At noncytotoxic concentrations of these oils, plaque formation was significantly reduced by 99% for Olbas and 66% for cajuput oil. The selectivity index of 150 for Olbas against herpes simplex virus was superior to a rather low selectivity index for cajuput oil. The mode of antiviral action of these essential oils was assessed by time-on-addition assays. Herpesvirus was significantly inhibited by pretreatment with Olbas essential oil prior to infection of cells. These results indicate that Olbas affected the virus before adsorption, but not after penetration into the host cell, thus Olbas exerted a direct antiviral effect on HSV. A clearly time-dependent antiviral activity for Olbas and cajuput oil could be demonstrated. Considering the lipophilic nature of the Olbas complex essential oil mixture, which enables it to penetrate the skin, and a high selectivity index, Olbas might be suitable for topical treatment of herpetic infections.