Polymerase chain reaction may not be useful to detect Coccidioides spp DNA in oropharyngeal, nasal, or conjunctival swab samples in dogs with newly diagnosed pulmonary coccidioidomycosis.

Upper respiratory swab PCR for Coccidioides spp lacks diagnostic value; serology remains the preferred diagnostic method.

This prospective cohort study evaluated the diagnostic utility of real-time multiplex quantitative PCR for detecting Coccidioides spp DNA from upper respiratory tract swab samples (nasal cavity, oropharyngeal, and conjunctival) in 24 client-owned dogs with newly diagnosed pulmonary coccidioidomycosis. Samples were collected between January and October 2024 using sterile cotton swabs. The multiplex PCR panel also tested for Blastomyces spp, Histoplasma spp, Pneumocystis jirovecii, and Pneumocystis canis DNA. Across all 72 PCR tests performed, zero samples yielded a positive result for Coccidioides spp DNA. In contrast, serological testing demonstrated strong diagnostic performance: agar gel immunodiffusion (AGID) detected anti-Coccidioides IgM antibodies in 46% of dogs and IgG antibodies in 71%, while enzyme immunoassay (EIA) detected IgG antibodies in 79% of dogs. Clinical outcomes were favorable, with 50% of dogs showing improvement and 42% achieving complete resolution of respiratory signs following approximately 3 months of oral fluconazole therapy. These findings indicate that PCR-based detection of Coccidioides spp DNA from upper respiratory mucosa swabs offers no meaningful diagnostic advantage in dogs with pulmonary coccidioidomycosis. Serological methods, particularly EIA for IgG, demonstrated superior sensitivity. Clinicians should rely on serology as the primary diagnostic modality when coccidioidomycosis is suspected, and should avoid upper respiratory swab PCR testing as a screening or confirmatory tool in this disease context.

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