Use of dog serologic data for improved understanding of coccidioidomycosis: A One Health approach

Background Coccidioidomycosis (Valley fever) occurs when animals and humans inhale spores of Coccidioides spp., soil-dwelling fungi of the southwestern United States. The spatial epidemiology of coccidioidomycosis is poorly understood due to irregular detection of Coccidioides in soil, disease underdiagnosis, and lack of nationwide mandatory reporting. Data on seroreactivity to Coccidioides among dogs—which are highly susceptible to coccidioidomycosis, widespread across the U.S, and have limited travel—may strengthen our understanding human disease risk. Methods We analyzed serologic test results for 834,899 dogs between 2012-2022 from all known diagnostic laboratories conducting serologic testing for anti-Coccidioides antibodies in dogs in the United States. We used testing date and county-level location data to estimate spatial and temporal trends in incidence and test positivity for dogs and compared them to human surveillance data. Results The overall seropositivity rate among tested dogs was 37.6% (313,829/834,899)­. Average test positivity rates in states with ≥ 0.5 tests/annum/10,000 households were 35.4% (Texas) to 74.1% (Montana). For these states, average annual incidence/10,000 households was: Arizona (87.8), New Mexico (0.89), Nevada (0.79), California (0.75), Montana (0.63), Colorado (0.41), Oregon (0.41), Texas (0.38), Idaho (0.37), Wyoming (0.34), Utah (0.32), and Washington (0.26). Human incidence in California and Arizona between 2012–2022 was significantly correlated with dog incidence (ρ = 0.75 and ρ = 0.65, respectively). The distribution of seropositive dogs expanded from 76/3,144 counties (2.4%) in 2012 to 390 in 2022 (12.4%). Conclusions Further investment in human diagnostic infrastructure and provider knowledge may ameliorate significant under-recognition of this emerging fungal disease.