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Phylogeny of a relapsing fever Borrelia species transmitted by the hard tick Ixodes scapularis.

ABSTRACT: The discovery of Borrelia species that were related to the agents of relapsing fever but were transmitted by hard ticks rather than soft ticks challenged previous taxonomies based largely on microbe-host specificities and geographic considerations. One of these newly-identified organisms is the Borrelia miyamotoi sensu lato strain LB-2001 from North America and transmitted by Ixodes scapularis. This or related strains have been identified as the cause of human disease, but comparatively little is known about their biology or genetics. Using recently acquired chromosome sequence of LB-2001 together with database sequences and additional sequences determined here, I carried out comparisons of the several species of Borrelia, including those in the two major clades: the relapsing fever group of species and the Lyme disease group of species. Phylogenetic inference at the species level was based on four data sets: whole chromosomes of ?1Mb each, and concatenated sequences of 19 ribosomal protein genes, 3 conserved nucleic acid enzymes (rpoC, recC, and dnaE), and 4 contiguous genes for nucleotide salvage on a large plasmid. Analyses using neighbor-joining, maximum likelihood, and Bayesian methods were largely concordant for each of the trees. They showed that LB-2001 and related hard tick-associated organisms, like Borrelia lonestari, are deeply positioned within the RF group of species and that these organisms did not, as some earlier estimations had suggested, constitute a paraphyletic group. The analyses also provided further evidence that major changes in host ranges and life cycles, such as hard to soft ticks or vice versa, may not correlate well with overall sequence differences. The genetic differences between LB-2001 and B. miyamotoi sensu stricto justify provisional use of the "sensu lato" designation for LB-2001.

SUBMITTER: Barbour AG

PROVIDER: S-EPMC4182126 | biostudies-literature | 2014 Oct

REPOSITORIES: biostudies-literature

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Phylogeny of a relapsing fever Borrelia species transmitted by the hard tick Ixodes scapularis.

Barbour Alan G AG

Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases 20140506

The discovery of Borrelia species that were related to the agents of relapsing fever but were transmitted by hard ticks rather than soft ticks challenged previous taxonomies based largely on microbe-host specificities and geographic considerations. One of these newly-identified organisms is the Borrelia miyamotoi sensu lato strain LB-2001 from North America and transmitted by Ixodes scapularis. This or related strains have been identified as the cause of human disease, but comparatively little i ...[more]

PMID: 24813576

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Project description:The blacklegged tick, Ixodes scapularis, is established in several regions of Ontario, Canada, and continues to spread into new geographic areas across the province at a rapid rate. This poses a significant public health risk since I. scapularis transmits the Lyme disease-causing bacterium, Borrelia burgdorferi, and other pathogens of potential public health concern. The objective of this study was to develop species distribution models for I. scapularis and B. burgdorferi to predict and compare the potential distributions of the tick vector and the Lyme disease pathogen as well as the ecological factors most important for species establishment. Ticks were collected via tick dragging at 120 sites across southern, central, and eastern Ontario between 2015 and 2018 and tested for tick-borne pathogens. A maximum entropy (Maxent) approach was used to model the potential distributions of I. scapularis and B. burgdorferi. Two independent datasets derived from tick dragging at 25 new sites in 2019 and ticks submitted by the public to local health units between 2015 and 2017 were used to validate the predictive accuracy of the models. The model for I. scapularis showed high suitability for blacklegged ticks in eastern Ontario and some regions along the shorelines of the Great Lakes, and moderate suitability near Algonquin Provincial Park and the Georgian Bay with good predictive accuracy (tick dragging 2019: AUC = 0.898; ticks from public: AUC = 0.727). The model for B. burgdorferi showed a similar predicted distribution but was more constrained to eastern Ontario, particularly between Ottawa and Kingston, and along Lake Ontario, with similarly good predictive accuracy (tick dragging 2019: AUC = 0.958; ticks from public: AUC = 0.863. The ecological variables most important for predicting the distributions of I. scapularis and B. burgdorferi included elevation, distance to deciduous and coniferous forest, proportions of agricultural land, water, and infrastructure, mean summer/spring temperature, and cumulative annual degree days above 0°C. Our study presents a novel application of species distribution modelling for I. scapularis and B. burgdorferi in Ontario, Canada, and provides an up to date projection of their potential distributions for public health knowledge users.

Project description:BackgroundRelapsing fever (RF) borreliae are arthropod-borne spirochetes and some of them cause human diseases, which are characterized by relapsing or recurring episodes of fever. Recently, it has been classified into two groups: soft tick-borne RF (STRF) borreliae and hard tick-borne RF (HTRF) borreliae. STRF borreliae include classical RF agents and HTRF borreliae, the latter of which include B. miyamotoi, a human pathogen recently identified in Eurasia and North America.ResultsIn this study, we determined the genome sequences of 16 HTRF borreliae strains: 15 B. miyamotoi strains (9 from Hokkaido Island, Japan, 3 from Honshu Island, Japan, and 3 from Mongolia) and a Borrelia sp. tHM16w. Chromosomal gene synteny was highly conserved among the HTRF strains sequenced in this study, even though they were isolated from different geographic regions and different tick species. Phylogenetic analysis based on core gene sequences revealed that HTRF and STRF borreliae are clearly distinguishable, with each forming a monophyletic group in the RF borreliae lineage. Moreover, the evolutionary relationships of RF borreliae are consistent with the biological and ecological features of each RF borreliae sublineage and can explain the unique characteristics of Borrelia anserina. In addition, the pairwise genetic distances between HTRF borreliae strains were well correlated with those of vector species rather than with the geographical distances between strain isolation sites. This result suggests that the genetic diversification of HTRF borreliae is attributed to the speciation of vector ticks and that this relationship might be required for efficient transmission of HTRF borreliae within vector ticks.ConclusionsThe results of the present study, together with those from previous investigations, support the hypothesis that the common ancestor of borreliae was transmitted by hard-bodied ticks and that only STRF borreliae switched to using soft-bodied ticks as a vector, which was followed by the emergence of Borrelia recurrentis, lice-borne RF borreliae. Our study clarifies the phylogenetic relationships between RF borreliae, and the data obtained will contribute to a better understanding of the evolutionary history of RF borreliae.

Dataset Information

Phylogeny of a relapsing fever Borrelia species transmitted by the hard tick Ixodes scapularis.

Publications

Phylogeny of a relapsing fever Borrelia species transmitted by the hard tick Ixodes scapularis.

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