A case of Blastomyces helicus pneumonia in a dog from a non-endemic region: diagnostic challenges and successful treatment outcome.

A 6-year-old Labrador Retriever presented with fever, cough, and labored breathing. Imaging revealed progressive pneumonia with intrathoracic lymphadenopathy. Initial testing yielded a positive Histoplasma urine antigen; however, fungal culture confirmed Blastomyces helicus. The dog improved on itraconazole, with normalization of clinical signs, C-reactive protein, imaging, and antigen tests. This case highlights diagnostic challenges of cross-reactivity in fungal antigen testing and emphasizes the importance of fungal culture in definitive diagnosis.