USGS Southwest Climate impacs Project

Soil and Ecological Habitats of the Occurrence of Coccidioides immitis, the Infectious Agent of Valley Fever

Mark Bultman, USGS, Tucson, AZ

Map showing occurrence of Valley Fever in the United States (from the University of Arizona Valley Fever Center of Excellence)

Coccidioidomycosis (valley fever) is an infection that is caused, in the overwhelming majority of cases, by inhalation of the arthroconidia of a soil-inhabiting fungus, Coccidioides immitis (C. immitis). The disease is a public health issue of increasing importance the southwestern U.S. as a result of rapid population growth, greater numbers of recreational visits and activities, and stationing of military personnel for active training in southwestern deserts. These demographic changes place an increasingly large unexposed population within endemic areas. Although many critical habitat parameters for C. immitis are known, the necessary and sufficient conditions for its occurrence in soils are not known. Our collaborative work with other institutions seeks to understand these conditions through chemical and biological analysis of soils, remote sensing to determine soil texture, analysis of epidemiological, canine epidemiological, climatic and geomorphologic data, and spatial modeling. The habitat parameters can then be used to define and predict regions of C. immitis infestation in soils. Our goal is to develop GIS/remotely sensed data-based habitat models for C. immitis in parts of the southwestern United States using existing information and new databases.

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