Scoles G A, Papero M, Beati L, Fish D
Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA.
Vector Borne Zoonotic Dis. 2001 Spring;1(1):21-34. doi: 10.1089/153036601750137624.
A species of Borrelia spirochetes previously unknown from North America has been found to be transmitted by Ixodes scapularis ticks. Infected ticks are positive for Borrelia spp. by DFA test but negative for Borrelia burgdorferi by polymerase chain reaction (PCR) using species-specific primers for 16S rDNA, outer surface protein A, outer surface protein C, and flagellin genes. A 1,347-bp portion of 16S rDNA was amplified from a pool of infected nymphs, sequenced, and compared with the homologous fragment from 26 other species of Borrelia. The analysis showed 4.6% pairwise difference from B. burgdorferi, with the closest relative being Borrelia miyamotoi (99.3% similarity) reported from Ixodes persulcatus in Japan. Phylogenetic analysis showed the unknown Borrelia to cluster with relapsing fever group spirochetes rather than with Lyme disease spirochetes. A 764-bp fragment of the flagellin gene was also compared with the homologous fragment from 24 other Borrelia species. The flagellin sequence of B. burgdorferi was 19.5% different from the unknown Borrelia and showed 98.6% similarity with B. miyamotoi. A pair of PCR primers specifically designed to amplify a 219-bp fragment of the flagellin gene from this spirochete was used to survey field-collected I. scapularis nymphs from five northeastern states (Connecticut, Rhode Island, New York, New Jersey, and Maryland). Positive results were obtained in 1.9-2.5% of 712 nymphs sampled from four states but in none of 162 ticks collected from Maryland. Transovarial transmission was demonstrated by PCR of larval progeny from infected females with filial infection rates ranging from 6% to 73%. Transstadial passage occurred from larvae through adults. Vertebrate infection was demonstrated by feeding infected nymphs on Peromyscus leucopus mice and recovering the organism from uninfected xenodiagnostic larvae fed 7-21 days later. Considering the frequency of contact between I. scapularis and humans, further work is needed to determine the potential public health significance of yet another zoonotic agent transmitted by this tick species.
一种此前在北美尚未发现的疏螺旋体属螺旋体已被发现可通过肩突硬蜱传播。通过直接荧光抗体试验（DFA）检测，受感染的蜱对疏螺旋体属呈阳性，但使用针对16S rDNA、外表面蛋白A、外表面蛋白C和鞭毛蛋白基因的种特异性引物进行聚合酶链反应（PCR）时，对伯氏疏螺旋体呈阴性。从一组受感染的若蜱中扩增出16S rDNA的1347碱基对片段，进行测序，并与其他26种疏螺旋体的同源片段进行比较。分析显示与伯氏疏螺旋体的成对差异为4.6%，最接近的亲缘种是在日本全沟硬蜱中发现的宫本疏螺旋体（相似度为99.3%）。系统发育分析表明，这种未知的疏螺旋体与回归热组螺旋体聚类，而不是与莱姆病螺旋体聚类。还将鞭毛蛋白基因的764碱基对片段与其他24种疏螺旋体的同源片段进行了比较。伯氏疏螺旋体的鞭毛蛋白序列与未知疏螺旋体的差异为19.5%，与宫本疏螺旋体的相似度为98.6%。一对专门设计用于从这种螺旋体中扩增鞭毛蛋白基因219碱基对片段的PCR引物，被用于检测从东北部五个州（康涅狄格州、罗德岛州、纽约州、新泽西州和马里兰州）野外采集的肩突硬蜱若蜱。在从四个州采集的712只若蜱中，1.9% - 2.5%的检测结果为阳性，但从马里兰州采集的162只蜱均未检测到阳性。通过对受感染雌性蜱的幼虫后代进行PCR检测，证实了经卵传播，子代感染率在6%至73%之间。经变态传递发生在从幼虫到成虫阶段。通过用受感染的若蜱叮咬白足鼠，然后从7至21天后喂食的未感染异种诊断幼虫中分离出病原体，证实了脊椎动物感染。考虑到肩突硬蜱与人类的接触频率，需要进一步开展工作来确定这种蜱传播的另一种人畜共患病原体的潜在公共卫生意义。
