Equine leptospirosis is an infectious bacterial disease caused by spirochetes belonging to Leptospira spp.
Horses across the country may be at risk.
Evidence indicates that exposure to Leptospira bacteria is common nationwide:
- A 45% seroprevalence was revealed in an analysis of diagnostic laboratory samples from 29 states and one Canadian province.1
- 75% of 5,261 healthy horses tested positive for at least one leptospiral serovar in a study involving 53 veterinary clinics in 18 states.2
Primary pathogen: L. pomona
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.
How are horses infected with leptospirosis?
The bacteria penetrate the mucous membranes of the eyes or mouth or enter through skin abrasions. Once in the bloodstream, leptospires can concentrate in the kidneys, be shed in the urine and cause serious medical problems.
Horses can become infected when exposed to bacteria in urine from:
- Contaminated soil, bedding, feed and drinking water4,5
- Standing or slow-moving water3,6
- Maintenance hosts such as skunks, white-tailed deer, raccoons and opossums
Genetics may play a role, as well. Appaloosas, Drafts and Warmblood breeds are more frequently and severely affected by Leptospira-associated uveitis than other breeds.7,8
Additionally, outbreaks of leptospirosis may be related to rainfall.6,9 Heavy rainfall can increase the risk of leptospiral abortions by as much as 3.7 times, with losses as high as $4.2 million for the Thoroughbred breed alone.1,9,10
A costly disease
$2.1 BILLION: the estimated economic impact of Leptospira-associated equine recurrent uveitis (ERU) in the U.S., including the cost of diagnosis, treatment and loss in horse value due to visual impairment or blindness.5,11-16
$102 MILLION: the estimated losses from Leptospira-associated abortions in Thoroughbred horses in Kentucky from 1993-2012.1
Leptospirosis is likely underdiagnosed.
Clinical signs associated with acute infection are general, such as fever, depression, anorexia and pain.17
Diagnostic testing can be challenging as the most commonly used diagnostic test is the Microscopic Agglutination Titer (MAT) test; however, a single titer does not differentiate between exposure and infection.18 Multiple titers taken at different times may be helpful in diagnosing disease, as well as other sophisticated tests.
1 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.
2 Data on file, Study Report No. Restricted Grant-FTLEPTO13 (v1.0) TI-01366, Zoetis LLC.
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. www.equinechronicle.com/leptospirosis-in-horses. Accessed September 6, 2016.
5 Spickler AR, Leedom Larson KR. Leptospirosis. http://www.cfsph.iastate.edu/DiseaseInfo/factsheets.php. Updated August 2013. Accessed September 6, 2016.
6 Levett PN. Leptospirosis. Clin Microbiol Rev. 2001;14(2):296-326.
7 Gerding JC, Gilger BC. Prognosis and impact of equine recurrent uveitis. Equine Vet J. In press. doi: 10.1111/evj.12451.
8 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.
9 Kinde H, Hietala SK, Bolin CA, Dowe JT. Leptospiral abortion in horses following a flooding incident. Equine Vet J. 1996;28(4):327-330.
10 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.
11 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;34:1300-1306.
12 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.
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. http://www.gao.gov/products/GAO-11-228. Published June 22, 2011. Accessed September 6, 2016.
16 Pick M, von Salis B, Schuele E, Schӧn 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 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.
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