Doctoral Dissertations

Date of Award

8-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Entomology, Plant Pathology and Nematology

Major Professor

Rebecca Trout Fryxell

Committee Members

Lisa Muller, James Fordyce, Laura Russo, and Daniel Grove

Abstract

Tick species and their associated pathogens are rapidly expanding their geographic range due to climate change, accidental introductions, and globalization. In the United States (US), exotic and invasive species such as Haemaphysalis longicornis interact with established tick species in the environment and on animal hosts. In addition, tickborne pathogens (TBP), novel and domestic, are continuing to expand geographically. Therefore, four research studies were dedicated to understanding ecological interactions of native and exotic tick species and their associated pathogens on human, companion, livestock, and wildlife hosts at varying geographic scales. First, forestry-related environmental variables were analyzed for their association on the abundance of ticks on human hosts in the southeastern US. Here we learned that each tick species, Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis, responds differently to biotic and abiotic variables which could be potentially mediated by their abundance. Next, we created environmental niche models (ENM) using GPS data from foresters encountering the tick species, A. americanum, D. variabilis, and I. scapularis. These maps are an important tool for implementing management strategies to control each tick species and can be used to reduce encounters with hosts. Next, ticks were collected through a Tennessee-statewide surveillance study from livestock and companion animal hosts and screened for Ehrlichia, Anaplasma, and Theileria pathogens to understand their current prevalence. Here we detected the occurrence of the devastating novel pathogen T. orientalis Ikeda in eastern Tennessee and an expanded geographic range of Ehrlichia and Anaplasma in the state. Finally, wildlife was sampled on farms in three eastern Tennessee counties infested with H. longicornis to understand ecological interactions between H. longicornis, on hosts, and established tick species. We demonstrated that the presence of H. longicornis can be predicted by host and established tick species life history characteristics. Through these research projects we identified host, tick, and environmental variables that are specific to established and an exotic tick species which can be targeted for tick control. We recommend that future studies further investigate how these variables affect tick presence on hosts and in the environment.

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