Date of Award

Summer 8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program/Concentration

Biomedical Sciences

Committee Director

David Gauthier

Committee Member

Wayne Hynes

Committee Member

Sandor Karpathy

Committee Member

Holly Gaff

Committee Member

Sinjini Sikdar

Abstract

Rickettsia parkeri is a tick-borne pathogen that causes R. parkeri rickettsiosis, a spotted fever rickettsiosis. The main vector of R. parkeri in the eastern United States is Amblyomma maculatum, also known as the Gulf Coast tick (GCT). The GCT has been undergoing a northward expansion from the original historic range. Whether R. parkeri expands with the GCT or has a local reservoir is unknown. Currently, there are R. parkeri-positive GCTs as far north as Delaware and New York. Expansion patterns for the GCT and R. parkeri remain unresolved but some studies point to long-distance host drop-offs as a potential cause. Additionally, the prevalence of R. parkeri in GCTs at the expansion front is higher than within the endemic areas. Three aims were accomplished to address the expansion and relationships of R. parkeri in the eastern United States.

The first aim of this study was to isolate, assemble and publish the genome of R. parkeri isolate Smith Island from a field collected eastern shore A. maculatum tick using delineated methodology from previous studies. This aim sets the methodology for following chapters.

The second aim investigated the phylogenomic relationships of R. parkeri isolates and their physical locations (collection sites). A 989 core protein set was generated and used for Maximum Likelihood phylogeny. The results suggest that R. parkeri isolates are being introduced to new areas via tick-mediated dispersal rather than states having a preexisting R. parkeri reservoir.

The final aim was to conduct an in silico analysis of intergenic regions (IGRs) from R. parkeri genomes and compare phylogenetic relationships inferred from protein-coding sequences and IGRs. Results from this aim demonstrated that sensu stricto isolates can be further genotyped; however, IGR-based phylogenies did not recover the same evolutionary relationships observed in protein-based phylogenies.

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DOI

10.25777/96sa-jz87

ISBN

9798193217206

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