Leptospirosis: A Hidden Threat

Equine leptospirosis can be a costly and underdiagnosed disease that can affect the entire equine industry.

From AQHA Corporate Partner Zoetis

Leptospirosis affects all regions of the country. Read on to learn about this bacterial infection and how it could affect your horse. Journal photo

Leptospirosis is a bacterial infection caused by spirochetes belonging to Leptospira species. A recent nationwide study showed 75 percent of healthy horses were exposed to at least one leptospiral serovar.1 The study involved 53 veterinary clinics across 18 states. Additionally, a 45 percent seroprevalence for Leptospira bacteria was revealed in an analysis of diagnostic laboratory samples from 29 states and one Canadian province.2

Horses are primarily affected by Leptospira interrogans serovar Pomona, or L. pomona, in North America.3 Although classified together, serovars are distinct variations within a species of bacteria. L. pomona is the leptospiral serovar most commonly associated with clinical disease in horses.3 The bacteria can colonize in the kidneys, circulate in the blood to other body organs and be shed in the urine.3 The bacteria can cause uveitis, or moon blindness (the most common cause of blindness in horses), as well as abortion and kidney failure. Kidney failure, especially in yearlings, can occur with renal infection associated with leptospires.1,3,4

Estimates show up to 70 percent of all uveitis cases are associated with leptospires.5,6 Additionally, Leptospira have been shown to cause up to 13 percent of equine bacterial abortions in endemic regions.3

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Horses can become infected with leptospires through contact with urine from wildlife, cattle and dogs. Standing water and rainfall can pose an increased risk. Additionally, outbreaks of leptospirosis may be related to rainfall.7,8 Heavy rainfall can increase the risk of leptospiral abortions by as much as 3.7 times.2,9

The bacteria penetrate the mucous membranes of the eyes or mouth or enter through skin abrasions.

Horses often become infected when exposed to bacteria in urine from:

  • Contaminated soil, bedding, feed and drinking water2,10
  • Standing or slow-moving water3,7
  • Maintenance hosts such as skunks, white-tailed deer, raccoons and opossums

Genetics may play a role as well. Appaloosas and Warmblood breeds are more frequently and severely affected by leptospiral-associated uveitis than other breeds.11,12

The impact of leptospirosis is felt emotionally in the loss of use or loss of a horse. However, the physical cost of the disease also is great. The estimated economic impact of leptospiral-associated equine recurrent uveitis in the United States totals $2.1 billion, including the cost of diagnosis, treatment and loss in horse value due to visual impairment or blindness.5,6,11,13-16

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Adding to the difficulty of this disease, leptospirosis often goes underdiagnosed. Clinical signs associated with leptospirosis are general, such as fever, depression, anorexia and pain.17 Additionally, veterinarians do not have a standard diagnostic tool to diagnose leptospirosis in horses. Veterinarians most commonly use the microscopic agglutination test for diagnosis; however, a single high titer does not differentiate between exposure and infection.18

You can discuss your horse’s risk level with your veterinarian and determine whether vaccination with LEPTO EQ INNOVATOR® is needed.

LEPTO EQ INNOVATOR from Zoetis is the first and only licensed equine leptospirosis vaccine to help prevent leptospirosis caused by L. pomona.*

*Currently, there are no vaccines available with USDA-licensed label claims against abortions, recurrent uveitis or acute renal failure caused by L. pomona.
1 Data on file, Study Report No. Restricted Grant-FTLEPTO13 (v1.0) TI-01366, Zoetis Inc.
2 Carter CN, Cohen N, Steinman MN, Smith JL, Erol E, Brown S. Seroepidemiology of equine leptospirosis utilizing diagnostic laboratory specimens from 29 states (US) and one Canadian province, in Proceedings. 55th Annu AAVLD Meet 2012;51.
3 Divers TJ, Chang Y-F. Leptospirosis. In: Robinson NE, Sprayberry KA, eds. Current Therapy in Equine Medicine. Vol 6. 6th ed. St. Louis, MO: Saunders Elsevier;2009:145-147.
4 Thomas H. Leptospirosis in horses. Equine Chronicle. January/February 2015. Available at: Accessed September 1, 2015.
5 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.
6 Borstel MV, Oey L, Strutzberg-Minder K, Boeve MH, Ohnesorge B. Direkter und indirekter Nachweis von Leptospiren aus Glasköperproben von Pferden mit ERU. Pferdeheilkunde. 2010;2(März/April):219-225.
7 Levett PN. Leptospirosis. Clin Microbiol Rev. 2001;14(2):296-326.
8 Kinde H, Hietala SK, Bolin CA, Dowe JT. Leptospiral abortion in horses following a flooding incident. Equine Vet J. 1996;28(4):327-330.
9 Erol E, Jackson CB, Steinman M, et al. A diagnostic evaluation of real-time PCR, fluorescent antibody and microscopic agglutination tests in cases of equine leptospiral abortion. Equine Vet J. 2015;47(2):171-174.
10 Spickler AR, Leedom Larson KR. Leptospirosis. Available at: Updated August 2013. Accessed September 1, 2015.
11 Gerding JC, Gilger BC. Prognosis and impact of equine recurrent uveitis. Equine Vet J. In press. doi:10.1111/evj.12451.
12 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.
13 Faber NA, Crawford M, LeFebvre RB, Buyukmihci NC, Madigan JE, Willis NH. Detection of Leptospira spp. In the aqueous humor of horses with naturally acquired recurrent uveitis. J Clin Microbiol. 2000;38(7):2731-2733.
14 Dwyer AE, Kalsow CM. Visual prognosis in horses with uveitis, in Proceedings. Amer Soc Vet Ophthalmol Annu Meet 1998;1-8.
15 GAO. Horse Welfare: Action Needed to Address Unintended Consequences from Cessation of Domestic Slaughter. Available at: Published June 22, 2011. Accessed September 1, 2015.
16 Pick M, von Salis B, Schuele E, Sch?n P. Der Verkehrswert des Pferdes und seine Minderungen (“Value of horses and its depreciations”). 3rd ed. Berlin, Germany: Veterinärspiegel Verlag GmbH; 2012.
17 Frellstedt L. Equine recurrent uveitis: A clinical manifestation of leptospirosis. Equine Vet Educ. 2009;21(10):546-552.
18 Timoney JF, Kalimuthusamy N, Velineni S, Donahue JM, Artiushin SC, Fettinger M. A unique genotype of Leptospira interrogans serovar Pomona type kennewicki is associated with equine abortion. Vet Microbiol. 2011;150(3-4):349-353
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