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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 developed severe pneumonia from an emerging fungal infection called Blastomyces helicus after traveling to Utah and Idaho. Initial blood tests incorrectly suggested a different fungus, but laboratory culture and genetic testing identified the true culprit. The dog was successfully treated with an antifungal medication called itraconazole and made a complete recovery with careful monitoring over 6 months.

Background

Blastomyces helicus is an emerging dimorphic fungal pathogen recently recognized as distinct from the classical Blastomyces dermatitidis. Unlike traditional blastomycosis endemic to the Mississippi and Ohio River valleys, B. helicus has been identified primarily in western United States and Canada. Veterinary cases are rarely reported and often diagnosed retrospectively.

Objective

This case report describes a culture-confirmed Blastomyces helicus pneumonia in a dog residing in a non-classical endemic region. The objective was to highlight diagnostic challenges of cross-reactivity in fungal antigen testing and emphasize the importance of fungal culture in definitive diagnosis.

Results

Urine antigen testing initially indicated Histoplasma, but fungal culture and DNA sequencing confirmed Blastomyces helicus. The dog responded well to itraconazole monotherapy with normalization of clinical signs, C-reactive protein, imaging findings, and antigen tests by 6 months. Complete resolution occurred with no disease recurrence after treatment discontinuation.

Conclusion

This case emphasizes the importance of considering B. helicus in dogs with pneumonia from non-endemic regions, particularly with travel history to western United States. Fungal culture and molecular sequencing are essential for definitive species identification when antigen cross-reactivity occurs. A comprehensive monitoring framework including serial imaging and quantitative antigen testing supports appropriate treatment duration and successful outcomes.
  • Published in:Medical Mycology Case Reports,
  • Study Type:Case Report,
  • Source: PMID: 41079968, DOI: 10.1016/j.mmcr.2025.100741
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