Nonulcerative keratouveitis as a manifestation of Leptospiral infection in a horse.

This study describes the case of a 2-year-old horse that presented with nonulcerative keratouveitis, an eye condition, which was eventually linked to a systemic infection with the bacteria Leptospira interrogans.

Introduction and Case Presentation

• The study begins with the presentation of a 2-year-old Thoroughbred filly exhibiting symptoms of ocular pain and excessive tearing in its left eye.
• The horse’s eye was noted to be miotic (abnormally small pupil), and its cornea (outer layer of the eye) was inflamed, particularly near the ventro-temporal limbus (edge of cornea). However, the cornea did not retain any fluorescein, a dye used in diagnosing eye conditions.

Treatment and Diagnosis

• Initially, various treatments, including topical antibiotics, atropine and diclofenac, and systemic flunixin meglumine and antibiotics, were implemented but did not alleviate the condition.
• Subsequently, the horse developed a pink, fleshy infiltrate near the limbus, indicating nonulcerative keratouveitis, a condition characterized by inflammation of the cornea and the uveal tract of the eye.
• The anterior uveitis (inflammation of the eye) worsened, as evidenced by dyscoria (abnormality of the pupil), hypopyon (presence of pus in the anterior chamber of the eye), and organized fibrin (clotted protein).

Further Tests and Findings

• The horse’s ocular signs improved temporarily with the application of topical and subconjunctival corticosteroids, but worsened whenever the frequency of medication was reduced.
• Serology tests revealed that the horse was positive for three serovars of Leptospira interrogans, a bacteria that causes leptospirosis, a disease that can affect many animals and humans.
• The horse was diagnosed as blind on the 91st day post presentation due to the absence of pupillary light and menace reflexes, indicators of vision. This led to the horse being donated for histopathological diagnosis.

Post-mortem Examination

• The post-mortem examination revealed that the corneal opacity was due to fibrosis (scarring tissue) and lymphocyte infiltration. Descemet’s membrane, the innermost layer of the cornea, was partly destroyed by macrophages (a type of white blood cell).
• The choroid (vascular layer of the eye) also displayed infiltration by lymphocytes, eosinophils and basophils (types of white blood cells) and showed presence of IgG and C3, indicating an immune response.
• Filamentous or spiral structures positive to Warthin-Starry staining, a technique used to detect certain bacteria, were found in the renal cortex (outer portion of the kidney).
• A polymerase chain reaction, a method used to amplify DNA, detected the presence of leptospiral genes in the kidney.

Conclusion

• The results indicated that the nonulcerative keratouveitis observed in the horse was caused by a systemic infection with Leptospira interrogans.