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

Summary

A dog from Colorado developed a severe respiratory infection that was initially mistaken for a bacterial pneumonia. After antibiotics failed to help, advanced testing revealed the dog had a fungal infection caused by Blastomyces helicus, a rare fungus found in western North America. The dog was successfully treated with an antifungal medication called itraconazole and made a complete recovery within six months, demonstrating the importance of considering fungal infections when standard treatments fail.

Background

Blastomyces helicus is an emerging dimorphic fungal pathogen recently recognized as a cause of pulmonary and disseminated mycoses in humans and animals. Previously referred to as Emmonsia helica, it has been identified primarily in western United States and Canada. The organism cross-reacts with galactomannan antigen assays for Histoplasma, potentially leading to diagnostic ambiguity.

Objective

This case report describes the diagnosis and treatment of culture-confirmed Blastomyces helicus pneumonia in a dog residing in a non-classical endemic region. The report emphasizes the diagnostic value of fungal culture in dogs with progressive pulmonary disease in non-traditional blastomycosis regions.

Results

Initial Histoplasma urine antigen testing was positive; however, fungal culture confirmed Blastomyces helicus. The dog improved on itraconazole monotherapy with normalization of clinical signs, C-reactive protein, imaging findings, and antigen tests. Complete resolution was achieved by six months of treatment with no disease recurrence after discontinuation.

Conclusion

This case highlights the importance of considering B. helicus as a cause of severe pneumonia in dogs outside traditional endemic areas and demonstrates the diagnostic value of fungal culture. Itraconazole monotherapy proved effective for treatment, and monitoring with quantitative antigen assays guided treatment duration based on individual clearance patterns.
  • Published in:Medical Mycology Case Reports,
  • Study Type:Case Report,
  • Source: PMID: 41079968, DOI: 10.1016/j.mmcr.2025.100741
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