Elucidating the role of rodent hosts on the transmission dynamics of coccidioidomycosis in California

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PROJECT SUMMARY Coccidioidomycosis is an infection caused by inhalation of spores from the soil-dwelling fungi Coccidioides immitis or C. posadasii, and can lead to chronic lung infection, meningitis, or death. Southwestern states are currently experiencing among the highest incidence rates of coccidioidomycosis ever recorded. The disease has levied a substantial human and economic burden throughout the southwest, totaling an estimated $2.2 billion in charges in California alone for coccidioidomycosis-associated hospitalizations from 2000-2011. Critical gaps in understanding have hindered the public health response, including how rodent host abundance and infection interacts to support pathogen transmission in the environment, as well as how environmental factors act in concert with reservoir hosts to sustain coccidioidomycosis incidence. To address these gaps, this project investigates the impacts of rodent host abundance and species characteristics, soil type, and environmental variability on rodent host infection prevalence and human coccidioidomycosis infection rates in California. The research focuses on three aims: 1) investigate the influence of host abundance on the spatiotemporal distribution of human cocci incidence using geolocated surveillance records from 2000 to 2018; 2) examine risk factors for rodent host infection and determine the specific soil conditions that are associated with rodent infection as compared to human infection; and 3) investigate how species-specific host abundance and infection prevalence interact to explain heterogeneity in risk of human cocci. In pursuit of these aims, we will combine georeferenced coccidioidomycosis case data across California since 2000 (N>65,000) at an unprecedented spatial resolution with longitudinal data on reservoir host abundance and infection. World-class existing data sources on host abundance will be leveraged including the Grinnell Resurvey Program (2003- 2016)--the most comprehensive field survey of small mammals in California--and small mammal monitoring programs of several state institutions. Through laboratory analysis of host specimens (N = 300) archived within UC Berkeley’s Museum of Vertebrate Zoology, the third largest mammal collection in the US, the research will identify specific soil conditions and host species posing the greatest risk for infection, and whether the abundance of certain host species are more implicated in human incidence. The results will yield the most comprehensive investigation of the role of rodent hosts on incidence of coccidioidomycosis, elucidating new insights into the environmental biology and epidemiology of the fungus. The knowledge gained will inform means of prevention by increasing understanding of whether rodent hosts are an important risk factor, identifying areas at highest risk given known species ranges, and improving predictions of incidence under climate and land use scenarios that modify host abundance. The proposed training will support my long term goal of a research career as an infectious disease epidemiologist with expertise in how the interaction of humans and animal hosts with their environment governs the transmission of multi-host zoonoses.