Graduate Studies

 

First Advisor

Clayton E. Cressler

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Elizabeth VanWormer, John DeLong, Larkin Powell, Tabitha Graves

Department

Biological Sciences

Date of this Version

7-2025

Document Type

Dissertation

Citation

A dissertation presented to the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Biological Sciences

Under the supervision of Professor Clayton E. Cressler

Lincoln, Nebraska, July 2025

Comments

Copyright 2025, Alexis Shannon Beagle. Used by permission

Abstract

Individuals that make up a population always display some level of variation between members. At the smallest scale, individuals always maintain genetic variation, but variation continues to arise at other scales of biological organization from physiological or immunological variation within individuals to variation in behavior between individuals that can be both genetically and environmentally mediated. The role of individual variation is particularly important in the context of infectious diseases because there is strong evidence that infections are highly heterogenous, indicating that patterns of individual variation drive a significant portion of the epidemiological patterns we observe. Individual variation leads to heterogeneity of within-host traits, such as virulence, shedding, or recovery, but also between host traits such as contact rate or space use. Variation in these traits explains the pervasiveness of super-spreading at the population scale and transmission hotspots on the landscape scale.

My research aims to explore how individual variation contributes to landscape level patterns of disease risk and epidemiology. I first review a globally relevant disease of concern, Chronic Wasting Disease (CWD) and illustrate the way that individual variation and a lack of integration of scale may contribute to contradictions in the literature. Then, I use simulations of an individual based SIR model to explore how within-host (co)variation of epidemiological traits contributes to super-spreading, epidemic size and epidemic fadeout. Finally, I construct landscapes of risk for elk on the National Elk Refuge, Jackson, WY by incorporating explicit movement data into a new disease modelling framework, MoveSTIR. My research reveals that individual variation, both within and between host, has the potential to dramatically alter the fate of an epidemic and distribution of risk on the landscape. However, the effect of individual variation will be dependent on external factors such as biology of the pathogen or environmental conditions, such as winter severity. To more fully understand and predict patterns of disease, research scientists should aim to explore what disease traits may be highly variable or even covary in their population of concern.

Advisor: Clayton E. Cressler

Download

Share

COinS