Croci Carlo, Erriquez Luca, Bisaglia Beatrice, Bellinzona Greta, Olivieri Emanuela, Sassera Davide, Castelli Michele
Department of Biology and Biotechnology, University of Pavia, Italy.
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Pavia, Italy.
Ticks Tick Borne Dis. 2024 Nov;15(6):102409. doi: 10.1016/j.ttbdis.2024.102409. Epub 2024 Nov 2.
Ticks are prominent vectors of several zoonotic diseases. Tick-borne pathogens include the members of the genus Ehrlichia, which are obligate intracellular bacteria infecting immune and hematopoietic cells. Ehrlichia muris predominantly affects rodents, but was also reported to be a human pathogen. The known geographical distribution of this bacterium ranges from Asia, to the USA and eastern Europe. In the present work, we report the finding of E. muris in an Ixodes ricinus tick collected from a migratory bird (Turdus iliacus) in Italy, southern Europe. We sequenced the total DNA from this tick sample, and, thanks to a dedicated bioinformatic pipeline, selectively assembled the genome of the bacterium, which represents the first one for E. muris from Europe. Phylogenetic and comparative genomic analyses were then performed. Accounting for tick species distribution, bird migratory routes, and molecular phylogeny of the bacterium, it is likely that this bird transported the tick to Italy from an endemic area of E. muris, such as eastern Europe. In addition, comparative genomic analyses highlighted that E. muris and other Ehrlichia spp. display copy number variations in two families of membrane proteins, likely due to recent gene duplication, deletion and recombination events. These differences are probably a source of variability for surface antigens to evade host immunity, with a potential role in host adaptation and specificity. The present results underline the impact of migratory birds on the spread of tick-borne pathogens towards non-endemic areas, highlighting the need for further epidemiological surveillance at bird ringing stations in Italy, and advocating further investigations on possible local transmission of E. muris in competent mammalian hosts.
蜱是多种人畜共患病的重要传播媒介。蜱传播的病原体包括埃立克体属的成员，它们是专性细胞内细菌，感染免疫细胞和造血细胞。鼠埃立克体主要感染啮齿动物，但也被报道为人畜共患病原体。这种细菌已知的地理分布范围从亚洲到美国和东欧。在本研究中，我们报告在欧洲南部意大利一只从候鸟（赤胸鸫）身上采集的蓖麻硬蜱中发现了鼠埃立克体。我们对该蜱样本的总DNA进行了测序，并通过专门的生物信息学流程，选择性地组装了该细菌的基因组，这是来自欧洲的首个鼠埃立克体基因组。随后进行了系统发育和比较基因组分析。考虑到蜱的物种分布、鸟类迁徙路线以及该细菌的分子系统发育，这只鸟很可能将蜱从鼠埃立克体的地方病流行区（如东欧）带到了意大利。此外，比较基因组分析突出显示，鼠埃立克体和其他埃立克体属物种在两个膜蛋白家族中存在拷贝数变异，这可能是由于近期的基因复制、缺失和重组事件导致的。这些差异可能是表面抗原逃避宿主免疫的变异性来源，在宿主适应和特异性方面具有潜在作用。本研究结果强调了候鸟对蜱传播病原体向非地方病流行区传播的影响，凸显了意大利鸟类环志站进一步开展流行病学监测的必要性，并倡导对鼠埃立克体在适宜的哺乳动物宿主中可能的本地传播进行进一步调查。
