Ellse L, Wall R
Veterinary Parasitology and Ecology Group, School of Biological Sciences, University of Bristol, Bristol, UK.
Med Vet Entomol. 2014 Sep;28(3):233-43. doi: 10.1111/mve.12033. Epub 2013 Oct 22.
There is a growing body of evidence indicating the potential value of essential oils as control agents against a range of arthropod ectoparasites, particularly lice, mites and ticks. Toxicity has been demonstrated following immersion and physical contact with treated surfaces, as well as after exposure to the vapour of these oils; the last of these factors implies that there is a neurotoxic, rather than simply a mechanical, pathway in their mode of action. However, the volatile nature of essential oils suggests that their residual activity is likely to be short-lived. A possible advantage of essential oils over conventional ectoparasite treatments may refer to their reported ovicidal efficacy, although it is unclear whether this results from neurotoxicity or mechanical suffocation. There are many difficulties in comparing the findings of existing studies of essential oil toxicity. One major issue is the wide variation among batches in the relative concentrations of oil constituents. A second issue concerns the fact that many experimental designs make it difficult to confirm that the effect seen is attributable to the oil; in many cases inappropriate controls mean that the effects of the excipient on mortality cannot be distinguished. Hence, it is important that an excipient-only control is always included in these bioassays. Furthermore, in direct contact assays, when attempting to identify the toxicity pathway of the essential oil tested, it is important to include a hydrophobic control. Without this, it is impossible to distinguish simple mechanical effects from neurological or other cellular toxicity. The use of essential oils in the control of veterinary ectoparasites is an area which holds considerable potential for the future and research into their use is still at an early stage. More extensive field trials, the standardization of components, the standardization of extraction, the standardization of good experimental design, mammalian toxicology profiling and excipient development, as well as further investigation into the residual activities and shelf-lives of these oils are all required to allow the full realization of their potential.
越来越多的证据表明，精油作为一系列节肢动物体外寄生虫，特别是虱子、螨虫和蜱虫的防治剂具有潜在价值。经浸泡、与处理过的表面进行物理接触以及接触这些油的蒸汽后均已证明其具有毒性；这些因素中的最后一个意味着其作用方式存在神经毒性途径，而不仅仅是机械途径。然而，精油的挥发性表明其残留活性可能是短暂的。与传统的体外寄生虫治疗方法相比，精油的一个可能优势可能在于其已报道的杀卵功效，尽管尚不清楚这是由神经毒性还是机械窒息导致的。比较现有精油毒性研究的结果存在许多困难。一个主要问题是不同批次的油成分相对浓度差异很大。第二个问题是，许多实验设计难以确认所观察到的效果归因于油；在许多情况下，不适当的对照意味着无法区分赋形剂对死亡率的影响。因此，在这些生物测定中始终包含仅含赋形剂的对照非常重要。此外，在直接接触试验中，当试图确定所测试精油的毒性途径时，包含疏水对照很重要。没有这个对照，就无法区分简单的机械效应与神经或其他细胞毒性。在兽医体外寄生虫防治中使用精油是一个未来具有相当潜力的领域，对其使用的研究仍处于早期阶段。需要进行更广泛的田间试验、成分标准化、提取标准化、良好实验设计标准化、哺乳动物毒理学分析和赋形剂开发，以及进一步研究这些油的残留活性和保质期，以充分实现其潜力。
