Virucidal Activity of Lemon Essential Oil against Feline Calicivirus Used as Surrogate for Norovirus

Virucidal effects of eucalyptus essential oil on porcine reproductive and respiratory syndrome virus

Currently, the efficacy of vaccination for preventing and controlling PRRSV is insufficient. Therefore, there is an urgent need for novel effective preventive strategies. This study aimed to investigate the antiviral effect of Eucalyptus essential oil (EEO) against PRRSV in vitro. Marc-145 cells were infected with PRRSV (rJXA1-R), and the toxicity of EEO in the cells was measured using the Cell Counting Kit-8 method. Additionally, the antiviral effect of EEO on PRRSV-infected cells was assessed using three treatment methods: drug administration post-PRRSV inoculation (post-treatment), drug administration before PRRSV inoculation (pre-treatment), and simultaneous drug administration and PRRSV inoculation (co-treatment). The EEO could not inhibit virus adsorption and/or replication since post-treatment and pre-treatment did not prevent viral infectivity. However, EEO exerted a significant virucidal effect on PRRSV. When PRRSV-infected cells were treated with 0.0156, 0.0312, and 0.0625% EEO, the cell survival rates were 55.37, 118.96, and 121.67%, respectively, and the titer of progeny virions decreased from 5.77 Log10TCID50 to 5.21 Log10TCID50, 0.55 Log10TCID50, and less than 0.167 Log10TCID50, respectively (where TCID50 is the 50% tissue culture infected dose). The fluorescence intensity of the PRRSV N protein significantly decreased in the indirect immunofluorescence assay. When cells were co-treated with EEO (0.0625%) and PRRSV (1000 TCID50) for 15 min, the viral particles were inactivated, and PRRSV (1000 TCID50) particles loss infectivity when the co-treatment time reached 60 min. In a word, EEO has no obvious therapeutic effect on PRRSV infection, but it can effectively inactivate virus particles and make them lose the ability to infect cells. These findings provide insights for the development and use of EEO to treat PRRS.

In Vitro Virucidal Activity of Different Essential Oils against Bovine Viral Diarrhea Virus Used as Surrogate of Human Hepatitis C Virus

The hepatitis C virus (HCV) is a major hepatotropic virus that affects humans with increased risk of developing hepatocellular carcinoma. The bovine viral diarrhea virus (BVDV) causes abortion, calf mortality and poor reproductive performance in cattle. Due the difficulties of in vitro cultivation for HCV, BVDV has been used as surrogate for in vitro assessment of the efficacy of antivirals. Essential oils (EOs) display antiviral and virucidal activity on several viral pathogens. In this study, the virucidal activity of five EOs, Salvia officinalis L. EO (SEO), Melissa officinalis L. EO (MEO), Citrus lemon EO (LEO), Rosmarinus officinalis L. EO (REO) and Thymus vulgaris L. EO (TEO) against BVDV was evaluated in vitro at different concentrations for several time contacts. MEO and LEO were able to considerably inactivate BVDV with a time- and dose-dependent fashion. MEO and LEO at the highest concentrations decreased viral titer by 2.00 and 2.25 log10 TCID50/50 μL at 8 h contact time, respectively. SEO, REO and TEO displayed mild virucidal activity at the highest concentrations for 8 h contact times. In this study, the virucidal efficacies of MEO and LEO against BVDV were observed regardless of compound concentration and contact time. Further studies are needed to confirm the potential use of MEO and LEO as surface disinfectants.

Assessing the virucidal activity of essential oils against feline calicivirus, a non-enveloped virus used as surrogate of norovirus

Norovirus (NoV) causes serious gastrointestinal disease worldwide and is regarded as an important foodborne pathogen. Due the difficulties of in vitro cultivation for human NoV, alternative caliciviruses (i.e., feline calicivirus, FCV, or murine NoV) have long been used as surrogates for in vitro assessment of the efficacy of antivirals. Essential oils (EOs) are natural compounds that have displayed antimicrobial and antioxidant properties. We report in vitro the virucidal efficacy of four EOs, Melissa officinalis L. EO (MEO), Thymus vulgaris L. EO (TEO), Rosmarinus officinalis L. EO (REO), and Salvia officinalis L. EO (SEO) against FCV at different time contacts (10, 30 min, 1, 4 and 8 h). At the maximum non-cytotoxic concentration and at 10- and 100- fold concentrations over the cytotoxic threshold, the EOs did not decrease significantly FCV viral titers. However, MEO at 12,302.70 μg/mL exhibited a significant efficacy decreasing the viral titer by 0.75 log10 Tissue Culture Infectious Dose (TCID50)/50 μl after 10 min as compared to virus control. In this study, virucidal activity of four EOs against FCV, was investigated. A lack of virucidal efficacy of TEO, REO and SEO at different compound concentrations and time contacts against FCV was observed whilst MEO was able to significantly decrease FCV titer.

Drug screening identified that handelin inhibits feline calicivirus infection by inhibiting HSP70 expression in vitro

Feline calicivirus (FCV) is considered one of the major pathogens of cats worldwide and causes upper respiratory tract disease in all cats. In some cats, infection is by a highly virulent strain of FCV (vs.-FCV), which can cause severe and fatal systemic disease symptoms. At present, few antiviral drugs are approved for clinical treatment against FCV. Therefore, there is an imminent need for effective FCV antiviral agents. Here, we used observed a cytopathic effect (CPE) assay to screen 1746 traditional Chinese medicine monomer compounds and found one that can effectively inhibit FCV replication, namely, handelin, with an effective concentration (EC50) value of approximately 2.5 µM. Further study showed that handelin inhibits FCV replication via interference with heat shock protein 70 (HSP70), which is a crucial host factor and plays a positive role in regulating viral replication. Moreover, handelin and HSP70 inhibitors have broad-spectrum antiviral activity. These findings indicate that handelin is a potential candidate for the treatment of FCV infection and that HSP70 may be an important drug target.

Comparison of the virucidal efficacy of essential oils (cinnamon, clove, and thyme) against hepatitis A virus in suspension and on food-contact surfaces

Essential oils (EOs) have been used for centuries as flavor enhancers in foods, and owing to their antimicrobial properties, they have potential as natural food preservatives. However, their effect on food-borne viruses is unknown. Therefore, in this study, the virucidal effects of three EOs (cinnamon, clove, and thyme) on the infectivity of the hepatitis A virus (HAV) were investigated. Different concentrations of each EO (0.05, 0.1, 0.5, and 1%) were mixed with viral suspensions in accordance with ASTM E1052-11:2011 and incubated for 1 h at room temperature. The EOs exhibited a concentration-dependent effect in the suspension tests, and HAV titers decreased by approximately 1.60 log PFU/mL when treated with EOs at the highest concentration of 1%. The antiviral effect of EOs treated at 1% for 1 h was also evidenced in surface disinfection tests according to the OECD:2013, as approximately 2 log PFU/mL reduction on hard food-contact surfaces (stainless steel and polypropylene) and approximately 2 and 1.4 log PFU/mL reduction on low-density polyethylene and kraft (soft food-contact surfaces), respectively. Moreover, RT-qPCR results revealed that HAV genome copies were negligibly reduced until treated with a high concentration (1%) in suspension and carrier tests. Overall, our findings highlighted the potential of cinnamon, clove, and thyme EOs as natural disinfectants capable of limiting HAV (cross-) contamination conveyed by food-contact surfaces. These findings advance our knowledge of EOs as antimicrobials and their potential in the food sector as alternative natural components to reduce viral contamination and improve food safety.