Emerging Antifungal Resistance in Canine and Feline Superficial Mycoses
A landmark study from St. George’s University has uncovered a critical and alarming trend in the treatment of superficial fungal infections in companion animals: complete resistance to the common antifungal drug fluconazole.
The research, the first of its kind in the Caribbean, identified the fungal pathogens causing skin and ear infections in Grenada's pet population and tested their susceptibility to four first-line azole drugs. The finding that 100% of the 79 clinical isolates were resistant to fluconazole has immediate implications for veterinary prescribing practices.
Study Snapshot: What Was Found
The team analyzed 405 samples from 136 dogs and 43 cats presenting with suspected fungal dermatitis or otitis. Key epidemiological findings include:
Predominant Pathogen: The yeast Malassezia pachydermatis was the most common isolate, found in 23% of dog ear samples.
Candida Presence: Candida tropicalis was identified in 7.6% of dog samples (skin and ear) but was absent in cats.
Dermatophyte Rarity: Only two dermatophyte isolates (Trichophyton spp.) were recovered, both from dogs. The classic cat-associated pathogen, Microsporum canis, was notably absent.
The Antifungal Susceptibility Crisis
The most critical part of the research involved testing the isolates against ketoconazole, itraconazole, voriconazole, and fluconazole. The results were stark:
Voriconazole 100%
Ketoconazole 97.5%
Itraconazole 94.9%
Fluconazole 0%
Clinical Implications and Expert Commentary
This level of uniform resistance is a serious clinical development since fluconazole is widely used because it's inexpensive, readily available, and generally well-tolerated. These findings force us to reconsider its place in our therapeutic arsenal, at least for regions with similar resistance patterns.
The authors hypothesize that the resistance likely stems from years of misuse and overuse of the drug, a problem potentially exacerbated by the agricultural use of similar compounds.
A Path Forward for Practitioners
The study does not leave practitioners without options. The high susceptibility to other azoles provides a clear alternative pathway.
First-Line Shift: Ketoconazole or itraconazole should be considered for first-line systemic therapy when a yeast infection is suspected or confirmed.
Diagnostic Vigilance: The study reinforces the paramount importance of in-clinic cytology. "You must know what you are treating," emphasized Dr. Alhassan. "A quick ear swab and cytology can confirm Malassezia overgrowth and justify moving directly to a more effective drug."
Culture and Sensitivity: For refractory or chronic cases, pursuing fungal culture and antifungal susceptibility testing is now a more justified investment.
The study concludes that while the prevalence of dermatophytes was lower than expected, the zoonotic potential of Trichophyton spp. means infection control and client education remain essential.
For now, the message to veterinarians is clear: in Grenada and potentially other tropical regions, the era of empirical fluconazole use for superficial fungal infections may be over.
Article: Brathwaite et al. (2025). Fungal Pathogens in Pet Dogs and Cats in Grenada: Identification and Antifungal Susceptibility. Journal of Fungi, *11*(8), 590.
DOI: https://doi.org/10.3390/jof11080590
