Inhibitory mechanism of cinnamon, clove, and thyme essential oils against murine norovirus and their anti-noroviral effect in suspension and on food-contact surfaces.

Human noroviruses (HuNoV) are a major cause of acute gastroenteritis and a growing public health concern. Essential oils (EOs) can be used as natural food additives with antiviral properties; however, the molecular mechanisms underlying their antiviral activity remain incompletely understood. This study investigated the impact of EOs on immune markers (IFN-α, TNF-α, IL-1β, IL-6, Mx, and OAS) in RAW 264.7 cells and their antiviral activity against murine norovirus (MNV-1 is used as a surrogate of human norovirus). RT-qPCR and ELISA results showed that EOs at non-cytotoxic doses (clove: 0.01 %, cinnamon: 0.01 %, thyme: 0.007 %) modulated inflammatory cytokines to create an environment that is unfavorable for viral replication; however, TNF-α was significantly induced, whereas only a small amount of IL-1β was detected, and IL-6 was undetected regarding protein levels. Virucidal effects were assessed in suspension and surface (stainless steel and low-density polyethylene) disinfection tests using EOs at concentrations of 0.5 % and 1 %, alone or combined with EDTA (50 or 200 mM). Both assays showed a < 1 log PFU/mL reduction in MNV-1 titers at 0.5 % and 1 % of EOs. EDTA enhanced the antiviral effects of EOs, with 1 % EOs + 200 mM EDTA being the most effective in reducing MNV-1 infection during both assays. The RT-qPCR results showed that the highest reduction (0.3-0.4 log genomic copies/sample) occurred with 1 % EOs + 200 mM EDTA in both assays. While our findings suggest that may exert antiviral effects potentially linked to inflammatory factor modulation, the results are correlative and do not establish a direct molecular mechanism. Further research is required to elucidate the precise interactions between host immune signaling and the viral replication process. These findings highlight EOs as promising natural alternatives for reducing viral contamination and enhancing food safety.