Q. Is there any food, treat, or climate that causes moon blindness flare-ups? My horse recently had one, and I want to prevent any more if possible. I already use a fly mask for "sunglasses." Paige

A. Unfortunately, we don't know what factors cause recurrence of inflammation in horses with equine recurrent uveitis (ERU) or "moon blindness." However, one of the causes of moon blindness is a bacterium, Leptospira interrogans, which produces a disease called leptospirosis. This bacterium is occasionally found in the urine of many species of wild and domestic animals. If the infected urine gets in a horse's feed or water, he might develop leptospirosis and eventually moon blindness. You can reduce the risk of horses getting leptospirosis by: 1) Keeping feed covered so rodents and other wild animals cannot gain access and contaminate it; 2) Eliminating standing water and fencing off ponds in pastures, as they can also be contaminated by urine from infected animals; and 3) Eliminating piles of junk such as old tires, brush, etc., that provide a habitat for rodents.

Several theories have been proposed to explain why subsequent attacks occur once a horse has moon blindness. The first is an autoimmune response, whereby the horse's immune system attacks the tissues of the eye. The second theory has to do with persistence of the bacterium, Leptospira interrogans, in the eyes of horses with moon blindness. This organism might periodically reactivate and multiply, causing inflammation.

Since we don't currently understand what causes the autoimmune response to recur, or the bacteria to reactivate and multiply, there are no recommendations for nutrition, management, or environment to prevent recurrent moon blindness attacks. Occasionally veterinarians will prescribe anti-inflammatory medication in order to lessen the severity of subsequent attacks of moon blindness.

About the Author

Barton W. Rohrbach, VMD, MPH, Dipl. ACVPM

Barton W. Rohrbach, VMD, MPH, Dipl. ACVPM, is an Associate Professor in the College of Veterinary Medicine at the University of Tennessee.

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