The recent pandemic of a novel H1N1 influenza emphasizes the urgency of identifying effective approaches to prevent viral infection. Between 1990 and 1999 in the United States, non-pandemic influenza A virus (IAV) infected 5-20% of people and caused approximately 36,000 deaths and 226,000 hospitalizations annually [1, 2]. IAV infection is initiated with a binding of the viral hemagglutinin (HA) to sialic acid on the cell surface; and virus particles are internalized through receptor-mediated endocytosis. While in the endosome, viral HA protein is activated and the virus fuses with endosomal membranes. After fusion, IAV shuts off host cell protein synthesis and cell replication. As a result, infected cells die by apoptosis or cytolysis.

Essential oils have been used for aromatherapy, massage therapy, emotional health, personal care, nutritional supplements, or cleaning for many years. The modern use of essential oils has grown rapidly as health scientists and medical practitioners have found scientific evidence for the benefits of this therapy. In Japan, Perillae Herba (a leaf of Perilla frutescens) has been prescribed to treat depression. It has been shown that l-Perillaldehyde, a major component in the essential oil containing in Perillae Herba, is responsible for the antidepressant-like activity through stimulation of the olfactory nerve [3]. Essential oil from Boswellia carteri and Boswellia serrata have been used for the treatment of rheumatoid arthritis and other inflammatory diseases in traditional medicine for many years [4, 5]. Studies showed that frankincense oil derived from Boswellia species possess anti-inflammatory activity though inhibition of immune cytokines production and leukocyte infiltration [6–8]. In addition, many other essential oils used in aromatherapy have medicinal properties including antiseptic properties [9], and mood enhancing effects [10, 11].

Distinctive chemical components of plants protect them from insects, bacteria or viruses that cause diseases. Essential oils prepared from plants, therefore, might be effective in protecting humans from viral infection. In addition to their intrinsic benefits to plants and as fragrances for people, essential oils have been used throughout history in many cultures for their medicinal and therapeutic benefits. They were first used in ancient Egypt for treatment of various illnesses and other physical and spiritual needs. Borrowing from the Egyptians, the Greeks, Romans, Indians, Persians, as well as Chinese began to refine distillation methods for extracting oils from aromatic plants and have used them extensively in medical practice for diverse purposes, such as promoting wellness, enhancing personal hygiene, and in therapeutic massage and aromatherapy. They have also been used as a beauty treatment, in food preparation, and in religious ceremonies.

In this study, we evaluated the effect of a commercially available essential oil blend, On Guard™, on influenza virus A/PR/8/34 (PR8) infection in Madin-Darby canine kidney (MDCK) cells. This oil blend combines a mixture of wild orange, clove, cinnamon, eucalyptus and rosemary. The mechanism of the oil-mediated inhibition of viral infectivity was also investigated.