Exploratory study of pesticide use and coccidioidomycosis

SUMMARY In 2023, California suffered the greatest number of cases of coccidioidomycosis (Valley fever) in its history. Climate change–in particular cycles of unusually wet and dry years–are suspected to be responsible for both local increases and the widening of this endemic fungus’ geographic distribution. Although outdoor laborers 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 are applied; loss of the pathogen would potentially lead to fewer local cases of disease. Alternatively, fallow land, that had previously been treated with pesticides may be permissive of recolonization with Coccidioides endospores through the pesticides’ disruption of competing microbial communities; this could lead to more cases of disease after the fallowing. We propose an exploratory study to evaluate whether pesticides are geographically and temporally linked to human coccidioidomycosis cases or environmental Coccidioides. We hypothesize that environmental pesticides, particularly fungicides and rodenticides, alter local coccidioidomycosis risk and seasonality by perturbing pathogen density within environmental reservoirs. We will take advantage of three data sets including: detailed, aggregated, publicly available pesticide use information to identify monthly applications of pesticides at the level of both the census tract and the individual residence from 2000 to 2023; monthly data previously obtained from the California Department of Public Health over the same time period on incident coccidioidomycosis cases; and data from our group on Coccidioides in 1500-2000 soil samples collected from the 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 for coccidiomycosis in California over a period of 20 years; and Aim 2) Evaluate environmental pesticide use, particularly fungicides and rodenticides, as a risk factor for Coccidioides detection in soil samples. Analyses will adjust for climatic factors and for specifics of land use, and will assess pesticides in general as well as rodenticides and fungicides. Understanding whether and how soil applications of antimicrobial agents like pesticides and fungicides affect coccidiomycosis incidence and Coccidioides distribution will provide insights into primary prevention of this infection in humans and animals. Future studies that may stem from this work include direct assessments of pesticide concentrations in soils with and without Coccidioides, as well as veterinary surveillance of animals in pesticide exposed areas. Project Number: 1R21AI191179-01 | Fiscal Year: 2025 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Julie Parsonnet (+1 co-PI) | Institution: STANFORD UNIVERSITY, STANFORD, CA | Award Amount: $247,621 | Activity Code: R21 | Study Section: Population based Research in Infectious Disease Study Section[PRID] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R21AI19117901