Ulcerative keratitis caused by beta-hemolytic Streptococcus equi in 11 horses.

The study investigates an instance of ulcerative keratitis in horses, a condition caused by the bacteria beta-hemolytic Streptococcus equi, describing its effects and the subsequent treatment options observed in eleven clinical cases from Florida, USA.

Research Methods

• The researchers conducted a clinical retrospective study over a three-year period (1996-1999).
• The study involved eleven horses which had been diagnosed with deep ulcers resulting from beta-hemolytic Streptococcus equi infections.
• The researchers focused on the correlation between this bacterial infection and the severity of the eye ulcers in the affected horses.

Findings

• Beta-hemolytic Streptococcus equi was identified as the cause of ulcers in all eleven horses, either associated with deep ulcers, descemetoceles, or iris prolapse, keratectomy/irradiation for corneal squamous cell carcinomas, and a suture abscess associated with a penetrating keratoplasty for a stromal abscess.
• The subspecies Streptococcus equi zooepidemicus was found in ten horses and the subspecies equi in one.
• There were significant signs of uveitis, including miosis and hypopyon in eight of the studied horses (72.7% of the cases).
• The diameter of the ulcers correlated with the beta-hemolytic Streptococcus, with a mean diameter of approximately 10.2mm.
• Concerning treatment, eight eyes required surgery (four grafts dehisced), with one requiring corneal transplantation. Two eyes were treated with medication only.
• The bacteria was found to be sensitive to a variety of antibiotics with varying degrees of efficacy, including ampicillin, bacitracin, cephalothin, chloramphenicol, gentamicin, polymyxin B, and tobramycin. However, all strains were resistant to neomycin.
• Healing time averaged around 44.7 days, and visual outcome was positive in eight of the eleven cases, while a total of nine retained the globe.

Conclusions

• The researchers concluded that Beta-hemolytic Streptococcus spp, which is a gram-positive bacteria, has the potential to cause severe clinical signs of aggressive ulcerative keratitis in horses, due to its ability to digest conjunctival graft tissue.
• While the prevalence of gram-negative bacteria and fungi are often linked to equine ulcers, this study highlights the potential harm that gram-positive bacteria can also cause.
• This study highlights the importance of an aggressive and intensive treatment approach combining both surgical interventions and medical therapy with topical antibiotics and protease inhibitors when addressing ulcerative keratitis caused by beta-hemolytic Streptococcus spp in horses.