Genetic identification of Borrelia burgdorferi spirochetes in Ixodes granulatus (Acari: Ixodidae) ticks and molecular phylogeny of I. granulatus ticks in the Taiwan area
Date Issued
2009
Date
2009
Author(s)
Chao, Li-Lian
Abstract
To identify the Borrelia burgdorferi spirochetes existed in Ixodes granulatus ticks of Taiwan, the genetic identities of spirochetes detected in I. granulatus ticks were determined by analyzing the gene sequences amplified by a genospecies-specific polymerase chain reaction (PCR) assay based on the outer surface protein A (OspA) of B. burgdorferi sensu lato. Results indicate that B. burgdorferi-like and B. valaisiana-related spirochetes were detected for the first time in Ixodes granulatus ticks collected in Taiwan. The phylogenetic analysis reveals that the sequence similarity among six strains of B. burgdorferi-like spirochetes is highly homogeneous, ranging from 90.5% to 98.7%, within the genospecies of B. burgdorferi sensu stricto and confirms that these spirochetes were genetically related to the genospecies of B. burgdorferi sensu stricto. However, seven strains of B. valaisiana-related spirochetes were classified as novel genospecies of B. burgdorferi sensu lato rather than B. valaisiana and that was clearly distinguished from other genospecies of Borrelia spirochetes. These results provide the first evidence of B. burgdorferi spirochetes detected in I. granulatus ticks of Taiwan. In addition, molecular phylogeny of I. granulatus ticks among the Ixodes species was also determined for the first time in Taiwan. The phylogenetic relationships were analyzed by comparing the sequences of mitochondrial 16S and nuclear ITS2 rDNA genes obtained from 19 strains of ticks representing seven species of Ixodes and two outgroup species (Rhipicephalus sanguineus and Haemaphysalis inermis). Four major clades can be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. Based on the mitochondrial 16S rDNA sequences, all these I. granulatus ticks of Taiwan were genetically affiliated to a monophyletic group with high homology (92.2-99.3%) in sequence similarity and that can be discriminated from other Ixodes species and other genus of ticks with a sequence divergence ranging from 11.7% to 30.8%. Moreover, intraspecific analysis revealed that two distinct lineages are evident between the same species of I. granulatus ticks collected from Taiwan and Malaysia. In contrast, the phylogenetic analysis based on the nuclear ITS2 rDNA sequences among various tick species also revealed a high genetic heterogeneity between I. granulatus ticks and other species of ticks. However, geographical variation was not observed between the same species of I. granulatus ticks collected from Taiwan and Japan. These observations may imply the feasibility of ITS2-based molecular targeting for species-specific identification of I. granulatus ticks in Asia area.
Subjects
Lyme disease
Borrelia burgdorferi
Ixodes granulatus
Tick
Taiwan
Type
thesis
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