Exploratory study of pesticide use and coccidioidomycosis

In 2023 California suffered the greatest number of cases of coccidioidomycosis (Valley fever) in itshistory. Climate changein particular cycles of unusually wet and dry yearsare suspected to be responsiblefor both local increases and the widening of this endemic fungus geographic distribution. Although outdoorlaborers are at higher risk of coccidioidomycosis that other individuals agricultural soil is less likely than non-agricultural soil to harbor the pathogen raising the possibility that pesticides alter environmental colonization.Fungicides could directly kill Coccidioides resulting in reduced colonization of soil where pesticides areapplied; loss of the pathogen would potentially lead to fewer local cases of disease. Alternatively fallow landthat had previously been treated with pesticides may be permissive of recolonization with Coccidioidesendospores through the pesticides disruption of competing microbial communities; this could lead to morecases of disease after the fallowing. We propose an exploratory study to evaluate whether pesticides are geographically and temporallylinked to human coccidioidomycosis cases or environmental Coccidioides. We hypothesize that environmentalpesticides particularly fungicides and rodenticides alter local coccidioidomycosis risk and seasonality byperturbing pathogen density within environmental reservoirs. We will take advantage of three data setsincluding: detailed aggregated publicly available pesticide use information to identify monthly applications ofpesticides at the level of both the census tract and the individual residence from 2000 to 2023; monthly datapreviously obtained from the California Department of Public Health over the same time period on incidentcoccidioidomycosis cases; and data from our group on Coccidioides in 1500-2000 soil samples collected fromthe Central Valley. We will then use a variety of sophisticated statistical methods to address two aims: Aim 1)Evaluate environmental pesticide use particularly fungicides and rodenticides as a risk factor forcoccidiomycosis in California over a period of 20 years; and Aim 2) Evaluate environmental pesticide useparticularly fungicides and rodenticides as a risk factor for Coccidioides detection in soil samples. Analyses willadjust for climatic factors and for specifics of land use and will assess pesticides in general as well asrodenticides and fungicides. Understanding whether and how soil applications of antimicrobial agents like pesticides and fungicidesaffect coccidiomycosis incidence and Coccidioides distribution will provide insights into primary prevention ofthis infection in humans and animals. Future studies that may stem from this work include direct assessmentsof pesticide concentrations in soils with and without Coccidioides as well as veterinary surveillance of animalsin pesticide exposed areas.