Anti-influenza virus activity of essential oils and vapors

Few satisfactory therapeutic agents are available for the control of Influenza virus, largely because of the continual emergence of drug-resistant mutants. Some essential oils (EOs) have demonstrated effective antimicrobial and antiviral properties in experimental conditions, but most of these studies tested the liquid oil phases, which are generally less practical and are potentially toxic for oral applications. In the present study, we evaluated several EOs and some of their major constituents for their possible anti-influenza virus properties in both liquid and vapor phases. In vapor phase Citrus bergamia, Eucalyptus globulus, and the isolated compounds citronellol and eugenol were very active against influenza virus following exposures of only 10 minutes. Pelargonium graveolens, Cinnamomum zeylanicum, Cymbopogon flexuosus were also very active with 30 minutes exposure. In liquid phase, Cinnamomum zeylanicum, Citrus bergamia, Cymbopogon flexuosus and Thymus vulgaris displayed 100% inhibitory activity at 3.1 μL/mL concentration. Under these conditions the vapors showed no measurable adverse effect on epithelial cell monolayers. This suggests that these oils in their vapor phases could be potentially useful in influenza therapy. The oil vapors were also evaluated for possible direct effects on the principal external proteins of the influenza virus, namely the HA (hemagglutinin) and NA (Neuraminidase). Several of the vapors inhibited the HA activity, but not the NA activity, suggesting that interaction with HA is a possible mechanism for the antiviral activity. Thus some of these oil vapors could have therapeutic benefits for people suffering from influenza, and possibly other membrane containing respiratory viruses.