The inhibitory effect of monoterpene, phenylpropanoid and sesquiterpene components of essential oils against herpes simplex virus

Herpes simplex virus type 1 (HSV-1) is an important pathogen for humans causing labial herpetic infections and serious disease in immunosuppressed patients. The development of resistant strains of HSV to the available drugs, especially acyclovir, has further attempted to identify and develop new alternative agents for management of HSV-1 infections. Essential oils and their components are potential antiviral agents. 11 monoterpenes e.g. α-terpinene, β-pinene and thymol, 2 phenylpropanoids, e.g. trans-anethol and 6 sesquiterpenes, e.g. β-caryophyllene, caryophyllene oxide and farnesol from essential oils were screened to evaluate their inhibitory effect against HSV-1 in vitro. All components were tested for cytotoxicity in a standard neutral red assay. These components from essential oils exhibited a high and concentration dependent activity against herpes simplex virus in RC-37 cells. The potential inhibitory effect against HSV-1 of monoterpenes, phenylpropanoids and sesquiterpenes was analysed by plaque reduction assays and the 50% inhibitory concentrations (IC₅₀) were determined in dose response studies. β-pinene, β-caryophyllene and caryophellene oxide showed potent selectivity indices of 24, 25 and 140, respectively. At maximum noncytotoxic concentration, herpes virus infectivity was reduced by 100% for β-pinene, by 98% for β-caryophyllene and by 84% for caryophyllene oxide. Most components revealed high antiviral activity against HSV due to direct inactivation of viral particles. We conclude that components of essential oils are highly effective antiherpetic agents.