Lepto What?

Leptospirosis may not be one of the biggest health issues facing horses, but it is one that bears watching.

Leptospirosis, a bacterial disease that can affect most mammals, including humans, is a common word in the livestock world, but not the equine one. But, when leptospirosis affects horses, it can cause abortion and recurrent uveitis, or “moon blindness.”


The disease is caused by spirochetes (motile bacteria) called leptospires. They are shed in the urine of deer, raccoons and rodents as well as from cattle, sheep and other livestock. Horses are most often infected through the mucous membranes of the eyes and mouth, but also sometimes through broken skin. The incubation period is one to three weeks and symptoms include fever, lethargy, poor appetite, swollen eyes, tearing, discharge from the eyes, redness and/or cloudiness in the eyes and mid- to late-term abortion. In rare cases, adult horses can become jaundiced and die from kidney or liver failure.

It is possible to positively identify the organism via a blood or urine test. “Unfortunately, the diagnostic test to confirm the presence of leptospiral antibodies in serum is a difficult one and is not offered at many labs around the country,” states Craig Carter, DVM PhD Dip. ACVPM , director of the Livestock Disease Diagnostic Center and professor of Epidemiology at the University of Kentucky. “A fluorescent antibody test can be used to confirm abortions.”

Carter has focused on leptospirosis for several years and feels that leptospirosis often goes undiagnosed and unreported. “The Bluegrass area of Kentucky experienced a significant number of leptospiral abortion cases in 2006. Our traceback study in 2007 estimated losses of $3.5 million, with only 48 percent of farms reporting. I personally believe that leptospiral abortion is happening around the U.S. We just aren’t confirming them.”

The bacteria like to cluster in certain areas, especially the eyes, kidneys, liver or reproductive tract. If it settles in the eyes, it causes painful uveitis. Severe cases, left untreated, can cause blindness, glaucoma and atrophy of the eye.

Abortion happens when the spiral-shaped bacteria invades the uterus or placenta, which in turn causes fetal death. If the mare does go full term and is infected, the foal may be sick or stillborn.


Once positively identified, treatment should start as soon as possible. For eye problems, steroids decrease inflammation, help ease eye muscle spasms, photosensitivity and tearing—but first rule out corneal ulcers. In addition, keeping the horse out of the direct sun and using a fly mask to protect the eyes will help. Antibiotics such as oxytetracycline, streptomycin or penicillin, while not as effective in eye problems, are used to treat any acute or chronic bacterial infection the horse has. The benefit of these treatments is quite variable.


Like many illnesses, it’s best to try and stop them before they start. Unfortunately, this is difficult with leptospirosis. With so little equine research, we don’t know how many horses are affected and to what extent. Currently, there is no vaccine, but advances are being made (see below).

Prevention comes down to taking proper care of your horses and facility. “Good management is truly the only means of prevention for the horse right now,” says Carter. “However, it is very difficult to isolate horses from wildlife reservoirs of leptospirosis.” Keeping wildlife out of hay and grain and removing stagnant/standing water help. If possible, keep horses away from water sources that wildlife or cattle use, and drain muddy areas. Turning horses out with cattle and sheep also increases their risk of exposure.

Breeders should isolate mares that have aborted pending a definitive diagnosis.

If leptospirosis has been positively identified, disinfect all areas where infected animals have been. Handlers should practice excellent hygiene when working with horses that have aborted.


According to Carter, leptospirosis research is ongoing. “A colleague of mine, Dr. Yung-Fu Chang at Cornell University, is working on developing strains of Leptospira focusing on outer membrane proteins (OMPs) that have promise for the development of better vaccines.

“As well, a graduate student of mine here at the University of Kentucky, Gloria Gellin, is doing a serological study of horse farm workers and equine veterinarians to help determine their risk of exposure to leptospira. Leptospirosis in all animal species (e.g. dogs, pigs, cattle, rodents) are known to infect humans, yet there are no studies looking into this for the horse. Her study may demonstrate that the leptospiral organism may possibly be transmitted from horses to humans under certain situations, lending strength to the idea of a vaccine for the horse.”






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