Ulcerative keratitis caused by beta‐hemolytic<i>Streptococcus equi</i>in 11 horses

Abstract

Abstract Purpose To describe 11 clinical cases of ulcerative keratitis in horses associated with betahemolytic Streptococcus equi in Florida, USA. Methods Retrospective clinical study (1996–99). Results Beta‐hemolytic Streptococcus equi was 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‐hemolytic Streptococcus equi subspecies zooepidemicus was found in 10 eyes and subspecies equi in 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 betahemolytic Streptococcus was 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. Conclusions Although 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‐hemolytic Streptococcus spp. 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.