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.

Objective To evaluate the diagnostic sensitivity of real-time PCR to detect Coccidioides spp DNA from oropharyngeal, nasal cavity, and conjunctival swab samples in dogs with pulmonary coccidioidomycosis.

Methods This was a prospective cohort study of client-owned dogs with newly diagnosed pulmonary coccidioidomycosis from January 2024 to October 2024. Sterile cotton swabs were gently rubbed within the nasal cavity and against the mucosa of the oropharynx and conjunctiva during the initial investigation for respiratory tract signs. Swabs were tested for Coccidioides spp, Blastomyces spp, Histoplasma spp, Pneumocystis jirovecii, and Pneumocystis canis DNA by multiplex quantitative PCR. Antibody serology assays (ie, agar gel immunodiffusion and enzyme immunoassay) were performed at a single reference diagnostic laboratory.

Results 24 dogs were included. Seventy-two PCR tests (nasal cavity, n = 24; oropharyngeal, 24; and conjunctival, 24) were performed, and none of the tests positively detected Coccidioides spp DNA. Forty-six percent (11 of 24) and 71% (17 of 24) of dogs had positive detection of anti-Coccidioides spp immunoglobulin M and G antibodies with agar gel immunodiffusion, respectively. Seventy-nine percent (19 of 24) of dogs had positive detection of immunoglobulin G antibodies with enzyme immunoassay. Respiratory tract signs improved (50%; n = 12) or completely resolved (42%; 10) after approximately 3 months of PO fluconazole administration.

Conclusions Coccidioides spp DNA was not detected in any swab sample from the upper respiratory tract.

Clinical Relevance Quantitative PCR to detect Coccidioides spp DNA from the nasal cavity, oropharynx, and conjunctiva using sterile cotton swabs provides no added diagnostic value in dogs with pulmonary coccidioidomycosis.