VALLEY FEVER HOT SPOTS: ENVIRONMENTAL FACTORS AFFECTING THE HABITAT AND SPATIAL DISTRIBUTION OF COCCIDIOIDES IN ARIZONA

Hundreds of thousands of cases of Coccidioidomycosis, or “Valley Fever,” a disease caused by the inhalation of soil-borne fungal arthroconidia (spores) of Coccidioides spp., occur annually in the United States. The endemic region of Coccidioides spp. in the United States has traditionally been defined as the Southwest; however, this region is expanding, largely driven by climate change. In highly endemic areas (California’s San Joaquin Valley [C. immitis] and Arizona’s Sonoran Desert [C. posadasii]), Coccidioides is not evenly distributed and is instead found in “hotspots.” Factors controlling the biogeography of Coccidioides spp. are not well defined, although soil, climatic, and environmental properties are expected to be important. Additionally, the ecological niche of Coccidioides spp. is still poorly understood, and it remains uncertain whether these fungi are primarily linked to small mammals, such as burrowing rodents, or if they exist as saprotrophs in soil.

To better define the physico-chemical soil characteristics of Coccidioides habitat, we collected both burrow and non-burrow soils from three locations in Arizona known to harbor Coccidioides. Coccidioides were more frequently detected in burrow soils (22%, n=18); however, we also detected it in non-burrow soils (9%, n=70). Soil characterization included particle size distribution, electrical conductivity, pH, solution and surface-adsorbed chemistry, organic carbon and nitrogen, and microbial biomass. Our preliminary results revealed emerging differences between burrow and non-burrow soils and between Coccidioides-positive and Coccidioides-negative soils, suggesting that soil parameters need to be considered when modeling the spatial distribution of Coccidioides. This work will contribute to the larger objective of developing a predictive geospatial model of C. posadasii incidence in the state of Arizona.