Equine keratomycosis: An international problem

Conjunctival bacterial and fungal flora in healthy horses in the UK

“…In other studies, however, molds have been less frequently isolated 11,15,16 . Most genera of molds are considered to be saprophytic, although are capable of causing disease as opportunists 2 . Aspergillus sp was cultured from three (5%) horses in the current study, although studies in other parts of the world have cultured this fungus from up to 71% of normal horse conjunctiva 14–16 .…”

“…In this series, Aspergillus sp was cultured in two cases, whilst in the remaining four, the diagnosis was based on histopathology or cytology. Keratomycosis is believed to develop when resident fungal organisms invade the corneal stroma secondary to a traumatically induced corneal defect 2 . Based on the low number of horses from which fungal organisms were isolated from the conjunctiva in the current study, it is possible that the relative scarcity of keratomycosis in the UK may be explained at least in part, by the low numbers of fungi present within the normal equine conjunctiva.…”

“…Ulcerative keratitis is a common clinical condition affecting horses throughout the world 1–3 . Although trauma is believed to be the initiating cause in most cases, secondary bacterial and fungal infection can result in serious sequelae such as corneal malacia which may require intensive and expensive treatment 4 .…”

Equine subepithelial keratomycosis

“…Undoubtedly, not all fungal ulcers in horses result directly from trauma with plant material. Inherent tear film instability, or tear film abnormalities induced by fungal organisms may allow fungi to destabilize the tear film and damage exposed corneal epithelial cells 1,3–8 . As the SEK evolves, breakdown of the epithelial intercellular junctions may occur to form faint fluorescein staining microerosions 9 .…”

“…Fungal keratopathies occur in several clinical forms in the horse. Microerosions, superficial and deep corneal ulcers, melting corneal ulcers, stromal plaques, corneal perforation and iris prolapse, and nonulcerative stromal abscesses are recognized to be caused by fungi in horses 1–8 . Equine keratomycosis is classically hypothesized to result from commensal conjunctival and corneal fungi attaching themselves to damaged corneal epithelial cells, the chemoattraction of leukocytes to the infection site, an elevation in tear film proteinases, and subsequent fungal colonization and proliferation 1,6–8 .…”