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Description of environmental parameters that indicate the presence of Coccidioides immitis, the causative agent of valley fever in the northwestern Mojave Desert
Coccidioidomycosis, also known as Valley Fever, is a re-emerging infectious disease of the American continent. Coccidioidomycosis is a respiratory disease caused by the inhalation of arthroconidia produced by the dimorphic ascomycete fungi Coccidioides immitis or Coccidioides posadasii known to live in soil environments as a saprophyte. Coccidioides sp. are known to thrive in loamy and highly saline soils. These fungi have the ability to form spores known as arthoconidia, which can survive the dry, hot summers. When soil is disturbed, spores become airborne and can cause infection when inhaled by a host. Recently, the incidence of valley fever has increased significantly in endemic areas of the pathogen such as the Western Mojave Desert and among the general public and has also affected prisoners incarcerated in correctional facilities, such as the one east of California City, our study area. The objective of this research was to determine the soil properties that are essential for the growth of Coccidioides immitis in the Northwestern Mojave Desert near California City. Different physical and chemical properties of soils such as soil pH and soil type are known to determine the distribution of plants, which can therefore indicate certain soil conditions, but these parameters also affect the growth of microorganisms and fungal communities in diverse microhabitats. The hypothesis of this project was that the presence or absence of the pathogen in the soil can be linked to yet to be determined environmental parameters and/or depends on the presence or absence of certain soil microorganisms that could act as antagonists to the pathogen. The physical and chemical soil parameters, as well as plant diversity were determined for each sampling site. In this study, culture independent techniques, such as DNA extraction followed by PCR and DGGE were used to detect the presence of C. immitis, and to determine the diversity of the soil fungal communities in 43 soil samples collected long several transects in 2014 and 2015. Results of this study revealed that the study area is highly endemic for the pathogen, but its presence could not be linked to specific soil parameters. The fungal diversity in the soil was generally low and showed the dominance of members of the Pleosporales and Hypocreales. Members of the fungal genus Ascobolus were only found in soils that were negative of the pathogen and could potentially include antagonists to C.immitis.
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