Walter Reed Project, Kenya Medical Research Institute, Kisumu, Kenya.
Vector Borne Zoonotic Dis. 2013 Jun;13(6):360-6. doi: 10.1089/vbz.2012.0977. Epub 2013 Mar 11.
Abstract Rickettsiae are obligate intracellular bacteria that cause zoonotic and human diseases. Arthropod vectors, such as fleas, mites, ticks, and lice, transmit rickettsiae to vertebrates during blood meals. In humans, the disease can be life threatening. This study was conducted amidst rising reports of rickettsioses among travelers to Kenya. Ticks and whole blood were collected from domestic animals presented for slaughter at major slaughterhouses in Nairobi and Mombasa that receive animals from nearly all counties in the country. Blood samples and ticks were collected from 1019 cattle, 379 goats, and 299 sheep and were screened for rickettsiae by a quantitative PCR (qPCR) assay (Rick17b) using primers and probe that target the genus-specific 17-kD gene (htrA). The ticks were identified using standard taxonomic keys. All Rick17b-positive tick DNA samples were amplified and sequenced with primers sets that target rickettsial outer membrane protein genes (ompA and ompB) and the citrate-synthase encoding gene (gltA). Using the Rick17b qPCR, rickettsial infections in domestic animals were found in 25/32 counties sampled (78.1% prevalence). Infection rates were comparable in cattle (16.3%) and sheep (15.1%) but were lower in goats (7.1%). Of the 596 ticks collected, 139 had rickettsiae (23.3%), and the detection rates were highest in Amblyomma (62.3%; n=104), then Rhipicephalus (45.5%; n=120), Hyalomma (35.9%; n=28), and Boophilus (34.9%; n=30). Following sequencing, 104 out of the 139 Rick17b-positive tick DNA had good reverse and forward sequences for the 3 target genes. On querying GenBank with the generated consensus sequences, homologies of 92-100% for the following spotted fever group (SFG) rickettsiae were identified: Rickettsia africae (93.%, n=97), Rickettsia aeschlimannii (1.9%, n=2), Rickettsia mongolotimonae (0.96%, n=1), Rickettsia conorii subsp. israelensis (0.96%, n=1), Candidatus Rickettsia kulagini (0.96% n=1), and Rickettsia spp. (1.9% n=2). In conclusion, molecular methods were used in this study to detect and identify rickettsial infections in domestic animals and ticks throughout Kenya.
立克次氏体是一种专性细胞内细菌，可引起动物源性和人类疾病。节肢动物媒介，如跳蚤、螨虫、蜱和虱子，在吸血时将立克次氏体传播给脊椎动物。在人类中，这种疾病可能危及生命。本研究是在肯尼亚旅行者中报告的立克次体病不断增加的背景下进行的。在位于内罗毕和蒙巴萨的主要屠宰场，从被屠宰的家畜身上采集了蜱虫和全血，这些家畜来自该国几乎所有的县。从 1019 头牛、379 只山羊和 299 只绵羊中采集了血液样本和蜱虫，并使用针对属特异性 17-kD 基因（htrA）的定量 PCR（qPCR）检测（Rick17b）检测立克次体感染。使用标准分类学关键来鉴定蜱虫。所有 Rick17b 阳性的蜱虫 DNA 样本均使用针对立克次体外膜蛋白基因（ompA 和 ompB）和柠檬酸合酶编码基因（gltA）的引物对进行扩增和测序。使用 Rick17b qPCR，在采样的 32 个县中的 25 个县（78.1%的流行率）发现了家畜的立克次体感染。牛（16.3%）和绵羊（15.1%）的感染率相当，但山羊（7.1%）较低。在采集的 596 只蜱虫中，有 139 只含有立克次体（23.3%），在安氏革蜱（62.3%；n=104）中检测率最高，其次是钝缘蜱（45.5%；n=120）、璃眼蜱（35.9%；n=28）和牛蜱（34.9%；n=30）。测序后，在 139 个 Rick17b 阳性蜱虫 DNA 中，有 104 个具有良好的 3 个靶基因的反向和正向序列。在将生成的共识序列查询 GenBank 时，以下斑点热群（SFG）立克次体的同源性为 92-100%：立氏立克次体（93.%，n=97）、拉氏立克次体（1.9%，n=2）、蒙古立克次体（0.96%，n=1）、康氏立克次体亚种。以色列（0.96%，n=1）、候选立克次体 kulagini（0.96%，n=1）和立克次体（1.9%，n=2）。总之，本研究使用分子方法检测和鉴定了肯尼亚各地家畜和蜱虫中的立克次体感染。
