Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Institute of Novel and Emerging Infectious Diseases, Südufer 10, 17493 Greifswald-Insel Riems, Germany.
Bundeswehr Institute of Microbiology, Department Virology and Rickettsiology, Neuherbergstr. 11, 80937 Munich, Germany.
Ticks Tick Borne Dis. 2018 Mar;9(3):500-505. doi: 10.1016/j.ttbdis.2018.01.009. Epub 2018 Feb 3.
Since the beginning of the 21st century, spotted fever rickettsioses are known as emerging diseases worldwide. Rickettsiae are obligately intracellular bacteria transmitted by arthropod vectors. The ecology of Rickettsia species has not been investigated in detail, but small mammals are considered to play a role as reservoirs. Aim of this study was to monitor rickettsiae in wild small mammals over a period of five years in four federal states of Germany. Initial screening of ear pinna tissues of 3939 animals by Pan-Rick real-time PCR targeting the citrate synthase (gltA) gene revealed 296 rodents of seven species and 19 shrews of two species positive for rickettsial DNA. Outer membrane protein gene (ompB, ompAIV) PCRs based typing resulted in the identification of three species: Rickettsia helvetica (90.9%) was found as the dominantly occurring species in the four investigated federal states, but Rickettsia felis (7.8%) and Rickettsia raoultii (1.3%) were also detected. The prevalence of Rickettsia spp. in rodents of the genus Apodemus was found to be higher (approximately 14%) than in all other rodent and shrew species at all investigated sites. General linear mixed model analyses indicated that heavier (older) individuals of yellow-necked mice and male common voles seem to contain more often rickettsial DNA than younger ones. Furthermore, rodents generally collected in forests in summer and autumn more often carried rickettsial DNA. In conclusion, this study indicated a high prevalence of R. helvetica in small mammal populations and suggests an age-dependent increase of the DNA prevalence in some of the species and in animals originating from forest habitats. The finding of R. helvetica and R. felis DNA in multiple small mammal species may indicate frequent trans-species transmission by feeding of vectors on different species. Further investigations should target the reason for the discrepancy between the high rickettsial DNA prevalence in rodents and the so far almost absence of clinical apparent human infections.
自 21 世纪初以来，斑点热立克次体病已被确认为全球新出现的疾病。立克次体是一种专性细胞内细菌，通过节肢动物媒介传播。立克次体物种的生态学尚未详细研究，但小型哺乳动物被认为起储存宿主的作用。本研究的目的是在德国四个联邦州的五年内监测野生小型哺乳动物中的立克次体。通过针对柠檬酸合酶（gltA）基因的 Pan-Rick 实时 PCR 对 3939 只动物的耳尖组织进行初步筛选，发现 7 种啮齿动物和 2 种鼩鼱的 296 只动物的立克次体 DNA 呈阳性。基于外膜蛋白基因（ompB、ompAIV）PCR 的分型鉴定出 3 个种：在四个调查的联邦州中，主要发生的种是瑞士立克次体（90.9%），但也检测到猫立克次体（7.8%）和拉乌尔立克次体（1.3%）。在所有调查地点，发现属 Apodemus 的啮齿动物中 Rickettsia spp.的流行率（约 14%）高于所有其他啮齿动物和鼩鼱的流行率。一般线性混合模型分析表明，黄颈鼠和普通田鼠的较老（较大）个体比年轻个体更常含有立克次体 DNA。此外，夏季和秋季在森林中收集的啮齿动物通常携带立克次体 DNA。总之，本研究表明，在小型哺乳动物种群中 R. helvetica 的流行率很高，并表明在一些物种和源自森林栖息地的动物中，DNA 流行率随年龄的增加而增加。在多种小型哺乳动物物种中发现 R. helvetica 和 R. felis DNA 可能表明媒介通过对不同物种的取食而频繁发生种间传播。进一步的研究应针对啮齿动物中高立克次体 DNA 流行率与迄今为止几乎没有明显临床感染的人类之间的差异的原因。
