Dipartimento di Scienze Veterinarie e Sanità Pubblica, Università degli Studi di Milano, Milano, Italy.
Parasit Vectors. 2013 Dec 12;6:350. doi: 10.1186/1756-3305-6-350.
The Midichloriaceae is a novel family of the order Rickettsiales, that encompasses intracellular bacteria associated with hard ticks (Ixodidae) and other arthropods. The most intensively investigated member of this family is Midichloria mitochondrii, a symbiotic bacterium of the sheep tick Ixodes ricinus, characterized by the capacity of multiplying inside the mitochondria. A recent study suggested that these bacteria might be inoculated into the human host during the tick bite. The purpose of this study was to determine the potential infectivity of Midichloria bacteria for non-human animals exposed to the risk of tick bite.
Blood from horses, cattle, sheep and dogs exposed to the risk of tick bite was included in this study. DNAs were extracted, and amplified using 16S ribosomal RNA primers conserved in the Midichloria genus. Furthermore, sera from dogs exposed to the risk of tick bite were analyzed in order to evaluate the presence of antibodies against the recombinant flagellar protein (rFliD) from M. mitochondrii using an ELISA test.
Here we present two lines of evidence that support the possibility that bacteria from the genus Midichloria are inoculated into vertebrate hosts during a tick bite: (i) a direct evidence, i.e. the detection of circulating DNA from bacteria related with M. mitochondrii, in the blood of vertebrates exposed to tick parasitism; (ii) a further indirect evidence, i.e. the presence of antibodies against an antigen from M. mitochondrii in dogs exposed to the risk of tick bite. It is interesting to note that variability was detected in the Midichloria gene sequences recovered from positive animals, and that some of these sequences were identical to those generated from tick-associated Midichloria.
Based on the results, and on the overall information so far published on the genus Midichloria, we suggest that these bacteria are likely to represent a novel group of vector-borne agents, with the potential of infecting mammalian hosts. Whether inoculation of Midichloria bacteria could cause a true infection and pathological alteration in mammalian hosts is still to be determined. Surely, results emphasize the relevance of Midichloria bacteria in investigations on tick immunology and tick-bite markers.
密螺旋体科是立克次体目中的一个新科，包含与硬蜱（硬蜱科）和其他节肢动物相关的细胞内细菌。该科研究最多的成员是绵羊蜱伊氏曼巴菌的共生细菌，其特征是能够在线粒体内部繁殖。最近的一项研究表明，这些细菌可能在蜱叮咬时接种到人类宿主中。本研究旨在确定暴露于蜱叮咬风险的非人类动物中密螺旋体细菌的潜在感染性。
本研究纳入了暴露于蜱叮咬风险的马、牛、绵羊和狗的血液。提取 DNA，使用在密螺旋体属中保守的 16S 核糖体 RNA 引物进行扩增。此外，分析了暴露于蜱叮咬风险的狗的血清，以使用 ELISA 试验评估针对密螺旋体属的重组鞭毛蛋白（rFliD）的抗体的存在。
我们提供了两条证据支持在蜱叮咬过程中细菌从密螺旋体属接种到脊椎动物宿主的可能性：（i）直接证据，即从暴露于蜱寄生的脊椎动物血液中检测到与 M. 相关的循环细菌 DNA；（ii）进一步的间接证据，即暴露于蜱风险的狗中存在针对 M. 密螺旋体抗原的抗体。有趣的是，从阳性动物中回收的密螺旋体基因序列存在变异，其中一些序列与来自与蜱相关的密螺旋体的序列相同。
基于这些结果以及迄今为止关于密螺旋体属的总体信息，我们建议这些细菌可能代表一组新的媒介传播剂，具有感染哺乳动物宿主的潜力。密螺旋体细菌的接种是否会导致哺乳动物宿主的真正感染和病理改变仍有待确定。毫无疑问，这些结果强调了密螺旋体细菌在蜱免疫和蜱叮咬标志物研究中的相关性。
