Ulcerative keratitis caused by beta‐hemolyticStreptococcus equiin 11 horses

Abstract

AbstractPurposeTo describe 11 clinical cases of ulcerative keratitis in horses associated with betahemolyticStreptococcus equiin Florida, USA.MethodsRetrospective clinical study (1996–99).ResultsBeta‐hemolyticStreptococcus equiwas cultured from 11 horses with deep ulcers, descemetoceles or iris prolapse (n= 8), a suture abscess found with a penetrating keratoplasty for a stromal abscess (n= 1), and ulceration that developed following keratectomy/irradiation for corneal squamous cell carcinoma (n= 2). Beta‐hemolyticStreptococcus equisubspecieszooepidemicuswas found in 10 eyes and subspeciesequiin one. Marked signs of uveitis including miosis and hypopyon were present in 8/11 (72.7%) eyes. Keratomalacia was severe in all eyes. The mean diameter of the ulcers associated with betahemolyticStreptococcuswas 10.2 ± 6.1 mm. Eight of the eyes required conjunctival flap surgery (four grafts dehisced) and one eye corneal transplantation. Two eyes were treated with medication only. Isolate sensitivity to antibiotics included ampicillin (6/11), bacitracin (11/11), cephalothin (11/11), chloramphenicol (11/11), gentamicin (5/11), polymyxin B (2/11), and tobramycin (1/11). All isolates were resistant to neomycin. The average healing time was 44.7 ± 26.7 days. The visual outcome was positive in 8/11 eyes, and the globe retained in 9/11 eyes.ConclusionsAlthough Gram‐positive bacteria predominate in the normal conjunctival microflora of horses throughout the world, Gram‐negative bacteria and fungi are more often isolated from equine ulcers. Beta‐hemolyticStreptococcusspp. are associated with a very aggressive ulcerative keratitis with the capability to digest conjunctival graft tissue. Clinical signs are pronounced. Aggressive surgical and intensive medical therapy with topical antibiotics and protease inhibitors is indicated.