Inhibitory effect of Melaleuca alternifolia (tea tree oil) on influenza A/PR/8 virus replication

Abstract number: 1733_302

Timpanaro R., Garozzo A., Bisignano B., Stivala A., Furneri P.M., Tempera G., Castro A.

Objectives: The Melaleuca alternifolia (Tea Tree) is a coniferous tree found in tropical regions, whose needles contain an essential oil that is used in medical and cosmetic products. The Tea Tree Oil (TTO) consists of about 50% oxygenated monoterpenes and 50% terpene hydrocarbons, terpinen-4-ol is the main active component. TTO has a wide spectrum of antimicrobial activity against bacteria, yeasts and fungi. The antimicrobial activity has been principally attributed to terpinen-4-ol. The aim of this study was to investigate the antiviral activity and the mechanism of action of Tea Tree Oil and its components, terpinen-4-ol, g-terpinene, p-cymene, a-terpinene, terpinolene and a-terpineol, against Influenza A/PR/8 virus subtype H1N1 in MDCK cells.

Methods: The inhibitory effect was studied by measuring hemoagglutinin units (HAU) and 50% cytopathic effect (CPE50). In order to study the mode of action of the TTO, we carried out a series of experiments, including virucidal assay, pre-treatment assay, inhibition of attachment assay and time of addition assay.

Results: The TTO, the terpinen-4-ol, the terpinolene, the a-terpineol were found to have an inhibitory effect on influenza virus replication at doses below the cytotoxic dose. No of the tested compounds showed virucidal activity nor any protective action for the MDCK cells.

The effect of compound on different steps of the replicative cycle of influenza virus in MDCK cells was studied by adding compound at various times after infection (0, 1, 2, 4, 6 and 9 h). Viral replication, assessed as HAU/mL and CPE50 24 h after infection, revealed that this was significantly inhibited only if TTO was added within 2 h of infection, indicating an interference with an early step of the viral replicative cycle of Influenza virus. The influence of the compound on the virus adsorption step, studied by the infective centre assays, indicated that TTO did not interfere with cellular attachment of virus.

Conclusion: These data suggest that TTO interferes with an early events of Influenza virus replication, after viral adsorption. Further studies are necessary to understand the precise mode of action of this compound.