Date of Award

Summer 2015

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

Committee Director

Wayne L. Hynes

Committee Member

Holly Gaff

Committee Member

David Gauthier

Committee Member

Allen Richards


Tick-borne pathogens are an increasing threat to human and animal health worldwide. In the United States, cases of Lyme disease, spotted fever rickettsioses, ehrlichiosis and anaplasmosis are on the rise. Factors related to emergence include appearance of a new pathogen, recognition of an existing pathogen and environmental changes that result in new exposure events. Despite the rise in tick-borne disease incidence within many states, including Virginia, there is a paucity of data related to the prevalence and distribution of ticks and tick-borne pathogens.

The first aim of this dissertation research was to determine the tick-borne pathogen composition within tick populations in southeastern Virginia. Since 2009, the vector ecology laboratory at Old Dominion University has been conducting year-round surveillance of tick populations within Hampton Roads. This research explores the pathogen composition within these tick populations, with a particular focus on emerging pathogens, including Rickettsia parkeri and Ehrlichia chaffeensis.

The second aim of this research was to determine the transmission dynamics of Rickettsia parkeri within its vector, Amblyomma maculatum. Although some rickettsiae are transovarially transmitted in ticks, little is known about the frequency and efficiency of this transmission route, and nothing is known regarding the transmission strategy of R. parkeri in A. maculatum. By understanding the dynamics of pathogen transmission within the tick, a broader knowledge of the disease system can be attained, and mathematical models to explore these dynamics can be parameterized.

The third aim of this research was to explore the potential for R. parkeri to spill over from A. maculatum populations into populations of Amblyomma americanum. A. americanum is an aggressive human-biting tick, represents 95% of the ticks encountered in southeastern Virginia, and is the most common tick found attached to humans in the southeastern and mid-Atlantic United States. Because of its common association with humans, A. americanum and the pathogens it transmits are an important threat to human health in southeastern states. The competence of A. americanum as a vector of R. parkeri was also investigated in this study.


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