Department of Medical Sciences, Uppsala University Hospital, Uppsala, Sweden.
PLoS One. 2010 Jan 5;5(1):e8572. doi: 10.1371/journal.pone.0008572.
Migratory birds are known to play a role as long-distance vectors for many microorganisms. To investigate whether this is true of rickettsial agents as well, we characterized tick infestation and gathered ticks from 13,260 migratory passerine birds in Sweden. A total of 1127 Ixodes spp. ticks were removed from these birds and the extracted DNA from 957 of them was available for analyses. The DNA was assayed for detection of Rickettsia spp. using real-time PCR, followed by DNA sequencing for species identification. Rickettsia spp. organisms were detected in 108 (11.3%) of the ticks. Rickettsia helvetica, a spotted fever rickettsia associated with human infections, was predominant among the PCR-positive samples. In 9 (0.8%) of the ticks, the partial sequences of 17kDa and ompB genes showed the greatest similarity to Rickettsia monacensis, an etiologic agent of Mediterranean spotted fever-like illness, previously described in southern Europe as well as to the Rickettsia sp.IrITA3 strain. For 15 (1.4%) of the ticks, the 17kDa, ompB, gltA and ompA genes showed the greatest similarity to Rickettsia sp. strain Davousti, Rickettsia japonica and Rickettsia heilongjiangensis, all closely phylogenetically related, the former previously found in Amblyomma tholloni ticks in Africa and previously not detected in Ixodes spp. ticks. The infestation prevalence of ticks infected with rickettsial organisms was four times higher among ground foraging birds than among other bird species, but the two groups were equally competent in transmitting Rickettsia species. The birds did not seem to serve as reservoir hosts for Rickettsia spp., but in one case it seems likely that the bird was rickettsiemic and that the ticks had acquired the bacteria from the blood of the bird. In conclusion, migratory passerine birds host epidemiologically important vector ticks and Rickettsia species and contribute to the geographic distribution of spotted fever rickettsial agents and their diseases.
候鸟被认为是许多微生物的长距离载体。为了研究立克次体是否也是如此，我们对瑞典 13260 只迁徙雀形目鸟类的蜱虫感染情况进行了特征描述并采集了蜱虫。从这些鸟类身上共采集到 1127 只硬蜱，并从其中 957 只蜱虫中提取 DNA 进行分析。使用实时 PCR 检测这些 DNA 以检测立克次体，然后对 DNA 进行测序以确定物种。在 108 只（11.3%）蜱虫中检测到立克次体。在 PCR 阳性样本中，主要是与人类感染有关的斑点热立克次体瑞士立克次体。在 9 只（0.8%）蜱虫中，17kDa 和 ompB 基因的部分序列与地中海斑疹热样疾病的病原体瑞氏立克次体 Monacensis 最为相似，该病原体以前在欧洲南部以及 IrITA3 立克次体菌株中被描述过。在 15 只（1.4%）蜱虫中，17kDa、ompB、gltA 和 ompA 基因与瑞氏立克次体菌株 Davousti、日本立克次体和黑龙江立克次体最为相似，它们都具有密切的系统发育关系，前两者以前在非洲的 Amblyomma tholloni 蜱虫中发现，以前在硬蜱中未检测到。感染立克次体的蜱虫在地面觅食鸟类中的感染率是其他鸟类的四倍，但这两组鸟类在传播立克次体方面的能力相同。这些鸟类似乎不是立克次体的储存宿主，但有一例似乎是鸟类带菌，蜱虫从鸟血中获得了细菌。总之，迁徙的雀形目鸟类宿主携带具有流行病学意义的媒介蜱虫和立克次体，并促进了斑点热立克次体病原体及其疾病的地理分布。
