Evaluation of the ocular surface mycobiota in clinically normal horses.
Authors: Walsh Mary L, Meason-Smith Courtney, Arnold Carolyn, Suchodolski Jan S, Scott Erin M
Journal: PloS one
Summary
# Evaluation of the Ocular Surface Mycobiota in Clinically Normal Horses Next-generation sequencing has revealed that healthy equine eyes harbour a diverse fungal community dominated by Leptosphaerulina, Cladosporium and Alternaria species, with composition significantly influenced by environmental conditions. Walsh and colleagues characterised the ocular mycobiota of seven stabled stallions and five pastured mares using ITS1 sequencing, identifying eight major fungal genera and demonstrating marked differences between housing types: pastured horses exhibited substantially greater fungal species richness, diversity and abundance of potentially allergenic or pathogenic genera including Aspergillus and Alternaria. These findings suggest that housing and environmental exposure fundamentally shape the equine ocular mycobiota in ways analogous to documented effects on skin and gastrointestinal microbiota. For equine practitioners, this baseline characterisation establishes that environmental factors—particularly pasture exposure—alter ocular fungal colonisation patterns in clinically normal horses, with implications for understanding predisposition to fungal ocular disease, seasonal conjunctivitis and allergic responses. Future research correlating mycobiota composition with clinical disease presentation and inflammatory markers may clarify whether specific fungal taxa contribute to ocular pathology or represent innocent bystanders, potentially informing preventive management strategies and topical treatment decisions for horses with recurrent ocular issues.
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Practical Takeaways
- •Pasture-kept horses naturally harbor a more diverse and abundant fungal ocular microbiota than stabled horses, which may influence susceptibility to fungal eye infections
- •Environmental management (pasture vs stabling) should be considered as a factor in horses with recurrent or persistent fungal ocular infections
- •Baseline knowledge of normal equine ocular mycobiota composition is now available to inform interpretation of abnormal eye conditions and guide preventive management strategies
Key Findings
- •Equine ocular surface mycobiota is dominated by Leptosphaerulina (22.7%), unclassified Pleosporaceae (17.3%), and Cladosporium (16.2%)
- •Pastured mares showed significantly greater fungal species richness and diversity compared to stabled stallions (Shannon p=0.0224, Chao1 p=0.0118)
- •Aspergillus and Alternaria spp. relative abundances were significantly increased in pastured mares (p=0.005 and p=0.002 respectively)
- •Housing environment significantly influences ocular surface fungal community composition and structure (Jaccard R=0.460, Bray-Curtis R=0.811, both p=0.001)