Department of Biochemistry, School of Medicine, University of Nairobi, P.O. Box 30197-00100, Nairobi, Kenya.
Sydney School of Veterinary Science (SSVS), University of Sydney, Sydney, NSWs, Australia.
Parasit Vectors. 2020 Aug 27;13(1):432. doi: 10.1186/s13071-020-04266-0.
The tick vector Rhipicephalus microplus which transmits Babesia spp. and rickettsial pathogens has not been reported in Kenya since 1998. More recently, the pathogenic Babesia bovis has been detected in cattle blood DNA. The status of R. microplus in Kenya remains unknown. This study employed morphological and molecular tools to characterize R. microplus originating from Kenya and assess the genetic relationships between Kenyan and other African R. microplus genotypes.
Ticks were collected in south-eastern Kenya (Kwale County) from cattle and characterized to investigate the existence of R. microplus. Genetic and phylogenetic relationships between the Kenyan and other annotated R. microplus reference sequences was investigated by analysis of the cytochrome c oxidase subunit 1 (cox1) gene. To further characterize Kenyan ticks, we generated low coverage whole genome sequences of two R. microplus, one R. decoloratus and R. appendiculatus. A B. bovis specific TaqMan probe qPCR assay was used to detect B. bovis in gDNA from R. microplus ticks.
Occurrence of R. microplus was confirmed in Kwale County, Kenya. The Kenyan R. microplus cox1 sequences showed very high pairwise identities (> 99%) and clustered very closely with reference African R. microplus sequences. We found a low genetic variation and lack of geographical sub-structuring among the African cox1 sequences of R. microplus. Four complete mitochondrial (mt) genomes for two R. microplus, one R. decoloratus and one R. appendiculatus were assembled from next generation sequence data. The mitochondrial genome sequences of the two Kenyan R. microplus ticks clustered closely with reference genome sequences from Brazil, USA, Cambodia and India forming R. microplus Clade A. No B. bovis was detected in the Kwale R. microplus DNA.
These findings confirm the presence of R. microplus in Kenya and suggest that R. microplus Clade A is prevalent in cattle in sub-Saharan Africa. These and other recent findings of widespread occurrence of R. microplus in Africa provide a strong justification for urgent surveillance to determine and monitor the spread of R. microplus and vector competence of Boophilus ticks for B. bovis in Africa, with the ultimate goal of strategic control.
自 1998 年以来，肯尼亚尚未报告传播巴贝斯虫病和立克次体病原体的壁虱载体微小牛蜱。最近，在牛血液 DNA 中检测到了致病性巴贝斯牛血液。肯尼亚微小牛蜱的现状尚不清楚。本研究采用形态学和分子工具对源自肯尼亚的微小牛蜱进行了特征描述，并评估了肯尼亚和其他非洲微小牛蜱基因型之间的遗传关系。
从肯尼亚东南部的 Kwale 县（肯尼亚）采集牛蜱，并对其进行特征描述，以调查微小牛蜱的存在情况。通过分析细胞色素 c 氧化酶亚单位 1（cox1）基因，研究了肯尼亚和其他注释的微小牛蜱参考序列之间的遗传和系统发育关系。为了进一步描述肯尼亚的蜱，我们对两种微小牛蜱、一种染色牛蜱和一种尾突牛蜱进行了低覆盖率全基因组序列生成。使用 B. bovis 特异性 TaqMan 探针 qPCR 检测 R. microplus 蜱 gDNA 中的 B. bovis。
在肯尼亚 Kwale 县证实了微小牛蜱的存在。肯尼亚微小牛蜱 cox1 序列显示出非常高的成对同一性（>99%），并且与参考非洲微小牛蜱序列聚类非常紧密。我们发现非洲微小牛蜱 cox1 序列之间遗传变异低且缺乏地理亚结构。从下一代测序数据中组装了两种微小牛蜱、一种染色牛蜱和一种尾突牛蜱的四个完整线粒体（mt）基因组。两种肯尼亚微小牛蜱蜱的线粒体基因组序列与来自巴西、美国、柬埔寨和印度的参考基因组序列密切聚类，形成微小牛蜱 A 群。在 Kwale 的微小牛蜱 DNA 中未检测到 B. bovis。
这些发现证实了肯尼亚存在微小牛蜱，并表明微小牛蜱 A 群在撒哈拉以南非洲的牛中普遍存在。这些以及其他最近在非洲广泛存在微小牛蜱的发现为紧急监测提供了强有力的理由，以确定和监测微小牛蜱的传播和 Boophilus 蜱对 B. bovis 的媒介能力，最终目标是进行战略控制。
