Valley fever, or coccidioidomycosis, is a disease caused by the Coccidioides immitis and Coccidioides posadasii fungal species that dwell in the soil but can become airborne and infect a human or mammalian host through their respiratory tract. Disease rates in the western U.S. have significantly increased over the past two decades, creating an emerging public health burden. Studies have been conducted that attempt to elucidate the association between environmental conditions and the growth and dispersal of the pathogen, yet the specific ecology of and environmental precursors to the disease remain uncertain.
This research project investigates the relationship between environmental variables and valley fever by modeling the spatial and temporal dynamics of the disease using varying techniques. Chapter 1 discusses relevant literature before discussing the challenges associated with studying valley fever. Chapter 2 analyzes the temporal relationships between valley fever and climatic variables, focusing on Kern County, California, an understudied region in the U.S. where valley fever is highly endemic. Chapter 3 focuses on a regional spatial analysis using ecological niche modeling to better understand the environmental factors that influence the overall spatial distribution of valley fever in the U.S. Finally, combining both spatial and temporal components, Chapter 4 uses a hierarchical Bayesian spatio-temporal model to investigate the patterns and drivers of this disease, focusing on state of California, which saw an approximate 200% increase in cases from 2014 to 2018.
Cumulatively, this work offers new insights on relationships between climate, landcover, and valley fever disease risk. Significant findings include climate variables explaining up to 76% of valley fever variability in Kern County, California, the significance of both climatic and landcover variables in characterizing the geographic distribution of the disease, and identification of patterns increasing risk in geographic regions of California not currently considered highly endemic. These findings advance scholarly understandings of valley fever's environmental disease drivers. The results of this research can be applied by public health officials in the allocation of surveillance and public education resources, focusing upon regions that are most likely to encounter the illness. / Doctor of Philosophy / Valley fever is a fungal disease that causes illness in over ten thousand people in the western U.S. every year. Disease rates have been increasing for the past two decades for unknown reasons, although previous research suggests that climatic variations are likely contributing factors. This research evaluated environmental factors with hypothesized relationships to valley fever disease rates. First, this dissertation explored time-series relationships between climatic factors and valley fever incidence in an understudied county in California. Research findings identified that climatic factors including precipitation from previous seasons and temperature were significantly associated with valley fever incidence in this county. Second, this dissertation assessed where valley fever is found in the western U.S. The likely spatial distribution for the disease was mapped and environmental variables influential to this distribution were identified; they included both climate and landcover variables. Finally, a model was developed to analyze patterns of disease risk in California that considered both space and time, and environmental risk factors potentially contributing to the observed patterns were assessed. Counties with increased risk were identified and significant environmental relationships with valley fever risk were confirmed. The results of this research can be applied by public health officials in allocating surveillance and public education resources, focusing upon regions that are most likely to encounter the illness.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/100732 |
| Date | 06 May 2019 |
| Creators | Weaver, Elizabeth Ann |
| Contributors | Geography, Kolivras, Korine N., Abbas, Kaja M., Thomas, Valerie A., Thomas, R. Quinn |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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