<i>In vitro</i> comparison of three common essential oils mosquito repellents as inhibitors of the Ross River virus

Background The essential oils of Cymbopogon citratus (CC), Pelargonium graveolens (PG) and Vetiveria zizanioides (VZ) are commonly used topically to prevent mosquito bites and thus the risk of infection by their vectored pathogens such as arboviruses. However, since mosquito bites are not fully prevented, the effect of these products on the level of viral infection remains unknown. Objectives To evaluate in vitro the essentials oils from Reunion Island against one archetypal arbovirus, the Ross River virus (RRV), and investigate the viral cycle step that was impaired by these oils. Methods The essential oils were extracted by hydrodistillation and analyzed by a combination of GC-FID and GC×GC-TOF MS techniques. In vitro studies were performed on HEK293T cells to determine their cytotoxicity, their cytoprotective and virucidal capacities on RRV-T48 strain, and the level of their inhibitory effect on the viral replication and residual infectivity prior, during or following viral adsorption using the reporter virus RRV-renLuc. Results Each essential oil was characterized by an accurate quantification of their terpenoid content. PG yielded the least-toxic extract (CC50 > 1000 μg.mL-1). For the RRV-T48 strain, the monoterpene-rich CC and PG essential oils reduced the cytopathic effect but did not display virucidal activity. The time-of-addition assay using the gene reporter RRV-renLuc showed that the CC and PG essential oils significantly reduced viral replication and infectivity when applied prior, during and early after viral adsorption. Overall, no significant effect was observed for the low monoterpene-containing VZ essential oil. Conclusion The inhibitory profiles of the three essential oils suggest the high value of the monoterpene-rich essential oils from CC and PG against RRV infection. Combined with their repellent activity, the antiviral activity of the essential oils of CC and PG may provide a new option to control arboviral infection.【背景】柠檬草（Cymbopogon citratus，CC）、香叶天竺葵（Pelargonium graveolens，PG）及岩兰草（Vetiveria zizanioides，VZ）的精油常被外用以预防蚊虫叮咬，从而降低蚊虫携带的病原体（如虫媒病毒（arboviruses））引发感染的风险。然而，由于无法完全避免蚊虫叮咬，这类产品对病毒感染程度的影响尚不明确。 【研究目的】评估留尼旺岛来源的三种精油对典型虫媒病毒——罗斯河病毒（Ross River virus，RRV）的体外作用，并探究这些精油对病毒复制周期环节的抑制作用。 【研究方法】采用水蒸气蒸馏法提取三种精油，并结合气相色谱-氢火焰离子化检测器（GC-FID）与全二维气相色谱-飞行时间质谱（GC×GC-TOF MS）技术对其成分进行分析。以HEK293T细胞为模型开展体外实验，测定三种精油对RRV-T48毒株的细胞毒性、细胞保护活性及杀病毒能力；同时使用报告病毒RRV-renLuc，检测精油在病毒吸附前、吸附过程中及吸附后对病毒复制水平与残余感染性的抑制效果。 【研究结果】通过精准定量三种精油的萜类化合物成分完成成分表征。其中PG精油的细胞毒性最低，半数细胞毒性浓度（CC50）>1000 μg·mL⁻¹。针对RRV-T48毒株，富含单萜类化合物的CC与PG精油可降低细胞病变效应，但未表现出杀病毒活性。采用报告病毒RRV-renLuc开展的给药时间点实验结果显示，CC与PG精油在病毒吸附前、吸附过程中及吸附后早期给药时，均可显著抑制病毒复制与感染性。整体而言，低单萜类含量的VZ精油未观察到显著抑制效果。 【研究结论】三种精油的抑制活性谱表明，富含单萜类化合物的CC与PG精油在对抗RRV感染方面具有较高应用价值。结合其驱避蚊虫的活性，CC与PG精油的抗病毒活性可为虫媒病毒感染的防控提供新的选择。