Persistence of plague : determining which environmental factors contribute to maintenance of Yersinia pestis within sylvatic cycles
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Plague is a prioritized zoonotic disease caused by Yersinia pestis, a gram-negative bacterium. Sylvatic cycles of rodent host and flea vectors have established endemic foci responsible for the long-term maintenance of Y. pestis. Within the geographic range of prairie dogs, it is not understood why regions have recurrent epizootics while others remain plague-free. Abiotic factors have been correlated to epizootics and field surveys have led to hypotheses on the role other rodent species and flea or host population fluctuations may have in initiating these occurrences. Field and laboratory studies analyzing how these variables may impact vector competency have led to contradictory results and disparity in experimental design. Vector competency is often studied in the context of early-phase transmission or biofilm-mediated transmission applying temporal or genetic restrictions to the design and subsequent analysis. Corresponding analyses with these transmission models results in the neglect of unique geographic variables and flea:host interactions associated with the natural system. The purpose of this work was to investigate edaphic factors associated with epizootic occurrences throughout the geographic range of prairie dogs and determine if these factors influence vector competency of the flea. Soil moisture, temperature, and characteristics influencing water infiltration and storage had positive associations to plague occurrences. The depth at which these factors were associated, and the soil taxonomy varied based on geographic location, leading to site specific soil sensor installation for long-term evaluation. Investigating the infection in the flea under different abiotic and biotic components indicated host bloodmeal, temperature, and humidity influenced proventricular colonization and transmission efficiency. Variation in these components can alter vector competency, suggesting ecological factors drive disease spread or long-term maintenance. Another mechanism for long-term maintenance was discovered and strong evidence that Y. pestis leaves the alimentary canal and is transovarially transmitted is provided. The presence of bacteria throughout development from egg to F1 progeny illustrates processes independent of defined transmission models contribute to disease spread and maintenance.
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Ph. D.