Locking down the dust: exploring the association between Coccidioides posadasii and biological soil crusts

Ramsey, Marieke Lena (2023) Locking down the dust: exploring the association between Coccidioides posadasii and biological soil crusts. Masters thesis, Northern Arizona University.

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Abstract

Valley fever, or coccidioidomycosis, is the disease caused by two endemic soil-inhabiting fungal pathogens, Coccidioides immitis and C. posadasii, found throughout arid regions of the southwestern United States, Mexico, Central, and South America. Humans and other animals contract the disease through the inhalation of infectious spores (arthroconidia) from the environment, and 40% of exposed individuals develop symptoms ranging from mild pneumonia to severe disseminating disease that could lead to death if untreated. There has been little effort to reduce exposure to Valley fever through environmental remediation and restoration of natural soil communities. Biological soil crusts (biocrust) are communities of cyanobacteria, lichens, mosses, liverworts, and many other microorganisms that live in and bind the top mineral soil layer in dryland ecosystems. These communities provide critical ecosystem functions including C and N fixation, soil stability against wind and water erosion, hydrological cycling, and thermo-tolerance. Restoration of biocrust in areas of high Coccidioides endemism could reduce Valley fever incidence via several mechanisms: 1) stabilizing the soil surface with biocrust should reduce the potential of Coccidioides arthroconidia to aerosolize and reduce fungal burden in the airborne dust; (2) directly decreasing the abundance of Coccidioides by changing the soil habitat to be less favorable for its growth, and/or (3) decreasing the abundance of Coccidioides indirectly by creating antagonism or competition from a more diverse and active soil microbiome. Our overarching research objective is to determine if soil remediation with biocrust can reduce the occurrence of Coccidioides spp. in the air and/or soil by stabilizing the soil surface, reducing associated dust, and increasing below-ground microbial competition. For the current study, I took the following approaches to address the above questions. In the field, biocrust restoration plots were sampled as well as neighboring rodent burrows for the detection of Coccidioides spp. All restoration plots had no detection of Coccidioides spp. while 10% of rodent burrows surrounding the restoration site were positive, indicating Coccidioides spp. is found in the area, and soils are more likely negative where biocrust is present. An in vitro preliminary experiment was conducted to test if biocrust reduced arthroconidia aerosolization between three treatment groups: no biocrust, disturbed biocrust, and full biocrust coverage. These findings provide evidence that restoration of natural dryland communities can decrease the human fungal pathogen burden in soil and dust. Management practices that reduce the disruption of soil surfaces and/or restore disturbances with biocrust may reduce the abundance of airborne soil pathogens, and thus reduce the spread of endemic pathogen ranges.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Biocrust; Coccidioides; restoration; Valley fever; Soil stabilization; Coccidioidomycosis
Subjects:	R Medicine > RA Public aspects of medicine
MeSH Subjects:	C Diseases > C02 Virus Diseases
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Biological Sciences
Date Deposited:	01 Oct 2025 17:13
Last Modified:	01 Oct 2025 17:13
URI:	https://openknowledge.nau.edu/id/eprint/6198

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