Wet spring weather may bring an increase in cases of ERU in horses. Equine recurrent uveitis, also known as moon blindness, is a painful condition where repeated occurrences of inflammation in the eye can cause permanent damage.
Horse's eye with chronic signs of uevitis
With ERU, the horse's immune system inappropriately attacks normal or host proteins in the eye, causing damage that can lead to blindness.
© 2018 by Dr Bozorgmanesh New window.
The inflammation may cause career or even life-ending complications, explains Jacquelin Boggs, DVM, MS, Dipl. ACVIM, senior technical services veterinarian with Zoetis. ERU is the most common cause of blindness in horses worldwide.1
ERU is characterized by repeated occurrences, or flares, over the course of the horse’s life. The painful flares can reoccur months or even years apart; however, the interval between flares often shortens over the horse’s lifetime.
With ERU, the horse’s immune system inappropriately attacks normal or host proteins in the eye, causing damage that can lead to blindness.
ERU can affect one or both eyes. You may notice an affected eye appearing cloudy or discolored. Your horse may squint or tear excessively, and the pupil may be constricted. These are frequently the first signs, with more severe changes to the eye developing with subsequent flare-ups.
There is no cure for ERU. Even with the best treatment, many horses that develop recurrent uveitis won’t return to their previous level of performance.2
Equine recurrent uveitis is a multifactorial disease with a number of initial triggers. While there are many potential triggers, research indicates that the No. 1 trigger is leptospiral organisms, representing up to 70% of the ERU cases.3,4
Potential risk factors for Leptospira-associated uveitis include:
- Access to standing water or ponds
- Seasons that are wetter than usual
- Pasture flooding
- Exposure to skunks, white-tailed deer, raccoons, opossums or other wildlife near your horse’s pasture or barn
- Keeping feed in open containers or feeding on the ground
- Other animals on the property that have had ERU or mares that have aborted
Leptospirosis is a bacterial infection caused by spirochetes belonging to Leptospira spp. Leptospira interrogans serovar Pomona, known as L. pomona, is most often associated with leptospirosis infections in horses in North America.2
L. pomona can colonize in the kidneys, be shed in the urine and cause horses to become septicemic.2 The bacteria are then circulated in the blood and can cause uveitis, or moon blindness (the most common cause of blindness in horses), as well as abortions and kidney failure.
Kidney failure, especially in yearlings, can occur with renal infection associated with leptospirosis.1-3
Horses can become infected with leptospires through contact with urine from wildlife, cattle and dogs. Standing water and rainfall can pose an increased risk.
A recent study shows 75% of healthy horses have been exposed to at least one leptospiral serovar.1
Sources
1 Dwyer AE, Crockett RS, Kalsow CM. Association of leptospiral seroreactivity and breed with uveitis and blindness in horses: 372 cases (1986-1993). J Am Vet Med Assoc. 1995;207(10):1327-1331.
2 Gerding JC, Gilger BC. Prognosis and impact of equine recurrent uveitis. Equine Vet J. 2016;48(3):290-298.
3 Polle F, Storey E, Eades S, et al. Role of intraocular Leptospira infections in the pathogenesis of equine recurrent uveitis in the southern United States. J Equine Vet Sci. 2014;34(11-12):1300-1306.
4 Borstel MV, Oey L, Strutzberg-Minder K, Boeve MH, Ohnesorge B. Direkter und indirekter Nachweis von Leptospiren aus Glask perproben von Pferden mit ERU. Pferdeheilkunde. 2010;2(M rz/April):219-225.
Press release by Zoetis - Edited article by Jacquelin Boggs, DVM, MS, Dipl. ACVIM