Antigen and antibody testing for the diagnosis of blastomycosis in dogs

Background: Early diagnosis and treatment are associated with an improved prognosis in blastomycosis. The diagnosis of blastomycosis may be missed by cytology, histopathology, culture, or serology. An enzyme immunoassay (EIA) for detection of Blastomyces dermatitidis galactomannan antigen in body fluids has been used for rapid diagnosis of blastomycosis in humans. Hypothesis: Measurement of Blastomyces antigen in urine or serum by the MVista Blastomyces antigen EIA is more sensitive than measurement of anti-Blastomyces antibodies for diagnosis of blastomycosis in dogs. Methods: Serum and urine samples from 46 dogs with confirmed blastomycosis were tested for Blastomyces antigen and serum was tested for anti-Blastomyces antibodies. Results: The sensitivity for the detection of antigen in urine was 93.5%, and it was 87.0% in serum. The sensitivity of antibody detection by agar gel immunodiffusion (AGID) was 17.4% and it was 76.1% by EIA. Antigen and antibody decreased during itraconazole treatment. Conclusions and Clinical Importance: Antigen detection is a more sensitive test for diagnosis of blastomycosis than antibody testing by AGID, the only commercially available method. Antigen concentrations decreased with treatment.