Signalment Risk Factors for Coccidioidomycosis Test Positivity in 887,764 Dogs, 2012-2023

Abstract: Background. Coccidioidomycosis (“Valley fever”) is an emerging infectious disease caused by Coccidioides spp., soil-borne fungi endemic to the southwestern United States. Following soil disturbance, humans and animals inhale aerosolized spores and can develop pneumonia and life-threatening disseminated disease. Previous studies suggested an increased risk of infection among certain dog breeds (e.g., vizslas, Weimaraners, Dalmatians) and among male dogs, yet it remains unclear whether this relates to digging behavior or a true increase in susceptibility (insufficient immune response). Hypothesis: That analysis of a large dataset of serologic test results would shed light on signalment risk factors for Coccidioides infection in dogs.Animals: 887,764 dogs tested for anti-Coccidioides antibodies across 7 diagnostic laboratories (2012 – 2023).

Methods: Chi-square analysis was used for statistical analysis; the group with test positivity (TP) closest to that of the total population as the reference for odds ratio (OR) calculations.

Results: Of 887,764 dogs, 37.3% were seropositive. Sex, breed, age, and size were identified for 91%, 77%, 75%, and 64% of dogs, respectively. Breeds with the highest and lowest ORs for TP were McNabs and Shetland sheepdogs, respectively (see table). ORs for TP were highest in large and medium sized dogs and lowest in toy sized dogs. ORs for TP were highest in neutered males and lowest in intact females. Seropositive dogs were younger than seronegative dogs; TP was highest in dogs 3 to 4 years of age. Conclusions and Clinical Importance: Findings suggest that both genetic and behavioral factors may explain susceptibility to coccidioidomycosis in dogs.