Center for Infection and Immunity of Lille (CIIL), INSERM U1019 - CNRS UMR 8204, Université Lille Nord de France, Institut Pasteur de Lille, Lille, France ; SaBio. Instituto de Investigación de Recursos Cinegéticos, IREC-CSIC-UCLM-JCCM, Ciudad Real 13005, Spain.
Institute of Parasitology, Biology Centre of the Academy of Sciences of the Czech Republic, České Budějovice, 37005, Czech Republic.
Front Zool. 2014 Jul 1;11:47. doi: 10.1186/1742-9994-11-47. eCollection 2014.
As an ecological adaptation venoms have evolved independently in several species of Metazoa. As haematophagous arthropods ticks are mainly considered as ectoparasites due to directly feeding on the skin of animal hosts. Ticks are of major importance since they serve as vectors for several diseases affecting humans and livestock animals. Ticks are rarely considered as venomous animals despite that tick saliva contains several protein families present in venomous taxa and that many Ixodida genera can induce paralysis and other types of toxicoses. Tick saliva was previously proposed as a special kind of venom since tick venom is used for blood feeding that counteracts host defense mechanisms. As a result, the present study provides evidence to reconsider the venomous properties of tick saliva.
Based on our extensive literature mining and in silico research, we demonstrate that ticks share several similarities with other venomous taxa. Many tick salivary protein families and their previously described functions are homologous to proteins found in scorpion, spider, snake, platypus and bee venoms. This infers that there is a structural and functional convergence between several molecular components in tick saliva and the venoms from other recognized venomous taxa. We also highlight the fact that the immune response against tick saliva and venoms (from recognized venomous taxa) are both dominated by an allergic immunity background. Furthermore, by comparing the major molecular components of human saliva, as an example of a non-venomous animal, with that of ticks we find evidence that ticks resemble more venomous than non-venomous animals. Finally, we introduce our considerations regarding the evolution of venoms in Arachnida.
Taking into account the composition of tick saliva, the venomous functions that ticks have while interacting with their hosts, and the distinguishable differences between human (non-venomous) and tick salivary proteins, we consider that ticks should be referred to as venomous ectoparasites.
作为一种生态适应，毒液在几种后生动物中独立进化。由于蜱虫主要以动物宿主的皮肤为食，因此被认为是主要的外寄生虫。蜱虫非常重要，因为它们是几种影响人类和家畜动物疾病的传播媒介。尽管蜱虫唾液中含有几种毒液分类群中存在的蛋白质家族，而且许多硬蜱属可以引起麻痹和其他类型的中毒，但由于蜱虫很少被认为是有毒动物，因此 tick 仍然被认为是有毒动物。蜱虫唾液以前被提议为一种特殊的毒液，因为蜱虫毒液用于吸血，可以对抗宿主的防御机制。因此，本研究提供了重新考虑蜱虫唾液毒性特性的证据。
基于我们广泛的文献挖掘和计算机研究，我们证明蜱虫与其他有毒动物具有许多相似之处。许多蜱虫唾液蛋白家族及其先前描述的功能与蝎子、蜘蛛、蛇、鸭嘴兽和蜜蜂毒液中的蛋白质同源。这推断出蜱虫唾液中的几个分子成分与其他公认的毒液分类群的毒液之间存在结构和功能的趋同。我们还强调了一个事实，即针对蜱虫唾液和毒液（来自公认的毒液分类群）的免疫反应均由过敏免疫背景主导。此外，通过比较人类唾液的主要分子成分（作为非毒液动物的一个例子）与蜱虫的唾液，我们发现有证据表明蜱虫更类似于毒液动物而不是非毒液动物。最后，我们介绍了我们对蛛形纲动物毒液进化的考虑。
考虑到蜱虫唾液的组成、蜱虫在与宿主相互作用时的毒液功能，以及人类（非毒液）和蜱虫唾液蛋白之间可区分的差异，我们认为蜱虫应被称为有毒的外寄生虫。
