Emerging infectious diseases represent a threat to biodiversity, posing significant challenges to wildlife conservation globally. Infectious diseases can cause population declines, local extirpations and, in rare cases, complete species extinction. Among emerging pathogens, pathogenic fungi have been responsible for drastic declines in several high-profile vertebrate taxa, such as Batrachochytrium dendrobatidis causing chytridiomycosis in many species of amphibians worldwide. Recently, an emerging infectious disease, 'snake fungal disease' (SFD), caused by the fungal pathogen Ophidiomyces ophidiicola, is affecting the health of snake populations in North America by causing skin infections which can be fatal. Given the potential impact of this disease on snake biodiversity worldwide, compounded by the pressure of anthropogenic stressors that already jeopardize the viability of many snake populations, there is a clear need for ecological research in this understudied system. This dissertation is comprised of 4 data chapters focusing on the disease dynamics of snake fungal disease in Europe, and the factors resulting in differential infection. In chapter 2, I develop a large field-based data collection in 10 countries in Europe to investigate the presence of disease hotspots and the variation of disease prevalence across host species, and to examine the pathogen genotypes that are present on the landscape. I found isolated areas of disease hotspots, and models including an interactive effect of host species and which pathogen clade are present on the landscape were best at explaining disease prevalence. In chapter 3, I perform a virulence challenge assay using 120 corn snakes (Pantherophis guttatus) and 7 strains of O. ophidiicola (3 collected from Europe, 4 from the USA). This experiment reveals that pathogen genotypes associated with higher disease prevalence in Europe also have higher pathogen virulence, and that different strains from the USA show variation in virulence. These results also match both physiological host responses measured in the lab and landscape patterns of disease. In chapter 4, I explore two mitigation-driven snake translocation projects in Europe that were complicated due to O. ophidiicola outbreaks. One snake species, N. tessellata, appears highly susceptible to SFD, indicating that under stressful conditions, O. ophidiicola can cause mortality regardless of pathogen genotype, and that this snake species may be important in pathogen maintenance. Finally in chapter 5, I report the presence of a different fungal pathogen in Spain, Parannannizziopsis sp., never reported in wild snakes in Europe before. Broadly, my dissertation demonstrates coevolutionary relationships between hosts and pathogens and has important implications to snake conservation over large scales. / Doctor of Philosophy / Biodiversity conservation is under significant threat globally due to the ever-growing human population. Threats such as habitat loss, climate change, pollution and infectious diseases are all important factors that are affecting wildlife populations. Snakes, and specifically infectious diseases of snakes, have been understudied compared to that of other types of wildlife in Europe. My dissertation focuses on understanding the disease ecology and conservation implications of snake fungal disease, an infectious disease that can be life-threatening to snakes. I first developed a study of this disease in multiple countries over three years to understand how common the disease is across the landscape, which species of snakes are most infected, and how severe skin infections are. I found specific areas in Europe where disease prevalence is high and attributed these higher disease areas to specific snake species and fungal strains that interact together to cause higher infection rates (chapter 2). Secondly, I designed a controlled experimental study in the laboratory to test the capacity of different pathogenic strains, collected in Europe and the USA, to harm its host. I chose a single host species, the corn snake (Pantherophis guttatus) to test this question. I found that different pathogen strains vary in their ability to cause severe disease, and these results were confirmed with field observations. I also found that one strain collected from coastal Virginia is able to cause more severe disease when compared to all other strains (chapter 3). Finally, I found that under captive stress, strains that might not be able to cause severe disease in the wild can lead to snake mortality, specifically in one snake species that might be more susceptible than others (chapter 4). Broadly, this dissertation describes complex interactions between snakes and fungal pathogens and has relevance to reptile conservation.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119548 |
| Date | 27 June 2024 |
| Creators | Blanvillain, Gaelle Jh |
| Contributors | Biological Sciences, Hoyt, Joseph R., Hawley, Dana Michelle, Uyeda, Josef C., Mims, Meryl C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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