Multi-locus DNA sequence analysis, antifungal agent susceptibility, and fungal keratitis outcome in horses from Southeastern United States.
Authors: Cullen Megan, Jacob Megan E, Cornish Vicki, VanderSchel Ian Q, Cotter Henry Van T, Cubeta Marc A, Carbone Ignazio, Gilger Brian C
Journal: PloS one
Summary
# Editorial Summary: Fungal Species Identification and Antifungal Therapy in Equine Keratitis Fungal keratitis remains a challenging condition in equine practice, yet treatment decisions often rely on genus-level identification rather than precise species classification. Cullen and colleagues analysed 32 cases of equine fungal keratitis from the Southeastern United States, using morphological assessment and multi-locus DNA sequencing to identify causative organisms and assess their antifungal susceptibility profiles. Aspergillus flavus and A. fumigatus dominated the Aspergillus isolates (83%), whilst 91% of Fusarium isolates nested within the F. solani species complex, representing nine genetically diverse lineages across both genera. Critical differences in drug susceptibility emerged between and within genera: Aspergillus species demonstrated superior susceptibility to voriconazole and terbinafine, whereas Fusarium species showed heightened sensitivity to thiabendazole, and natamycin efficacy varied significantly depending on the specific species involved. Whilst fungal species and lineage did not predict overall clinical outcome, Fusarium species were significantly more likely to cause stromal involvement (p = 0.045), underscoring the clinical relevance of precise identification. For equine practitioners, these findings underscore the necessity of species-level fungal identification—rather than presumptive genus-based treatment—to optimise antifungal selection and potentially improve therapeutic success rates in this sight-threatening condition.
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Practical Takeaways
- •Obtain species-level fungal identification (not just genus) before selecting antifungal therapy, as treatment efficacy varies significantly between species within the same genus
- •Consider Fusarium involvement when stromal keratitis develops; use thiabendazole preferentially for Fusarium and voriconazole or terbinafine for Aspergillus
- •Generic 'antifungal' approaches will likely fail; tailor drug selection to identified fungal species for better clinical outcomes in equine fungal keratitis cases
Key Findings
- •Aspergillus flavus, A. fumigatus, and Fusarium species (F. falciforme, F. keratoplasticum, F. proliferatum) were most common causative agents in 32 equine fungal keratitis cases
- •Fusarium species were significantly more associated with stromal keratitis (p = 0.045) compared to Aspergillus species
- •Species-level identification revealed differential antifungal susceptibility: Aspergillus more susceptible to voriconazole and terbinafine; Fusarium more susceptible to thiabendazole
- •Antifungal susceptibility patterns differed between individual species, demonstrating that genus-level identification is insufficient for optimal treatment selection