Uveitis Research Pinpoints Leptospira interrogans

A recent study published in the Journal of the American Veterinary Medical Association provides evidence that persistent ocular (eye) infection with the bacterium Leptospira interrogans is much more common in horses with recurrent uveitis than previously thought.

The species L. interrogans contains more than 218 separate strains, all of which are capable of producing the disease leptospirosis, which can affect people as well as a wide variety of animals.(For more on leptospirosis, see "Shared Diseases" on page 57.)

In this study, eyes from 242 horses with recurrent uveitis were tested for the presence of L. interrogans. These horses were undergoing vitrectomy (removal of the vitreous and replacement with an antibiotic solution) as a treatment. The researchers tested serum and vitreous humor (the jelly-like fluid that occupies the space between the retina and the back surface of the iris and lens) for evidence of infection with L. interrogans. These findings were compared with a control group of horses which had no history or clinical signs of recurrent uveitis, and were undergoing euthanasia or enucleation (removal of the eye) for other reasons.

Barton W. Rohrbach, VMD, MPH, Dipl. ACVPM, Associate Professor of Clinical Epidemiology at the University of Tennessee (UT) College of Veterinary Medicine, was a co-author of the study. He said, "The advantage of this particular study was the opportunity to test (culture) fluid from the eyes of a large number of horses with recurrent uveitis that underwent vitrectomy." Rohrbach and his colleagues found L. interrogans in the vitreous humor of 52% of the horses with recurrent uveitis. Duration of recurrent uveitis was more than a year for 38% of the horses from which L. interrogans was isolated.

"Although we were able to isolate L. interrogans from a large percentage of horses with recurrent uveitis, that is probably an under-representation of the frequency of infection because the organism can be difficult to isolate and it may undergo a latent phase," explained Rohrbach. "During the latent phase, L. interrogans is present, but may be difficult or impossible to find because it is in such low numbers; however, the organism may reactivate later when the horse's immune system is compromised, causing recurrence of uveitis."

The study provides a direction in which to focus future efforts for research into the prevention of recurrent uveitis.

"It is hoped that this study will stimulate new research into the use of antibiotics or possibly a vaccine in order to prevent and/or treat this disease," said Rohrbah. In terms of future UT research , Rohrbach and his colleagues are currently applying for funding to evaluate the use of a vaccine for preventing recurrent uveitis.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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