Leptospirosis in Horses

http://www.vet.cornell.edu/public/research/zweig/Newsletter/2001-07/index.html?/public/research/zweig/Newsletter/2001-07/leptospirosis.htm~StoryLeptospirosis in Horses

Watch Out for Leptospirosis

NEWS CAPSULE No. 31, July 2001

   Photo: The bacteria Leptospira interrogans can enter a horse's body through direct contact with blood, urine, or tissues from infected animals; through the mucous membranes of the eyes, nose, or mouth; or through a cut in the skin. (Photo courtesy of Yung-Fu Chang)

Leptospirosis is a growing problem for horse owners because there's no vaccine specifically for horses. As a result, leptospirosis can unpredictably infect horses and trigger fever, blindness, abortions, and even death. To prevent problems, horse owners are advised to keep an eye out for possible signs of leptospirosis and to take precautions to reduce the risks of infection.

Horses can get this bacterial disease, which also infects humans, cattle, wildlife, and most other animals, through the direct splashing of urine from infected animals (or from animals carrying the disease) into their eyes or from eating water, hay, or grain that's been contaminated by the urine of infected wildlife such as raccoons, mice, deer, or livestock .The bacteria can enter through direct contact with blood, urine, or tissues from infected animals; through the mucous membranes of the eyes, nose, or mouth; or through a cut in the skin. Not all horses that pick up the bacteria become ill, but if the immune system can't fight the infection, the bacteria can generate a lot of damage.

Leptospirosis respects no geographical or environmental boundaries. In recent years cases have been reported in horses in New York, Pennsylvania, and Kentucky. No one actually knows how many cases arise each year, although researchers do know that most horses in the Northeast, for example, test positive for having been exposed to leptospirosis.

If infected, a horse initially may develop a low fever for several days, lose its appetite, and seem dull or listless. Horse owners often first notice the disease when their horse develops painful-looking eyes caused by muscle spasms that close the eyes (severe blepharospasm), eyes sensitive to light (photophobia), eye discharge, tearing (lacrimation), squinting, puffiness around the eyes, eye cloudiness, or redness around the lids.

In addition to eye problems, leptospirosis can cause pregnant mares to abort. In fact, recent research shows that leptospirosis is one of the most important emerging causes of abortions in horses. Leptospirosis also can lead to decreased milk production, kidney failure, and death.

Diagnosing the infection is not always straightforward because no specific clinical signs are distinctive to leptospirosis although many of the symptoms do suggest the disease. Only laboratory tests can confirm a diagnosis. Prompt treatment, which may include steroids, antibiotics, and medications to dilate the eye, can relieve pain and minimize the chances of partial or total blindness. The horse may be more comfortable if it is kept in a dark stall or wears a fly-mask to protect against sunlight, dust, and insects.

Although leptospiral vaccines are available for farm animals and dogs, some outbreaks do still occur, perhaps because of vaccine inefficiency and/or because animals get infected by different Leptospira species than the vaccines protect for. With so many different Leptospira serotypes, no cross protection among them, and no vaccine available for horses, it's difficult to control or eradicate the disease. The vaccines for cattle are sometimes used in horses, but they don't protect against all the strains that may infect horses and can trigger side-effect reactions.

To better protect horses, researchers such as Yung-Fu Chang DVM, MS, PhD, DiplACVA, a professor of population medicine and diagnostic sciences, are working toward developing an equine vaccine. Chang, with a grant from the Harry M. Zweig Memorial Fund, is developing a genetic (DNA) vaccine or a recombinant vaccine against equine leptospirosis. He also is studying why Leptospira cause eye disease in horses, seeking to identify the protein(s) from Leptospira that can make antibodies against the equine eye tissues and cause autoimmune disease.

"It is very important that we develop a leptospiral vaccine that does not produce antibodies against normal horse eye tissues," Chang says.

Although horses don't easily spread leptospirosis to humans, the bacteria is contagious from animals to humans. Horse owners should assume that urine from any infected animal is potentially infectious and take the appropriate steps to protect themselves. People also can pick up leptospirosis from contaminated waters (such as ponds), direct contact with infected farm animals or rodents, or the blood or urine of infected animals, including pets. The disease is rarely fatal for humans.

To protect horses, owners should keep their animals from drinking stagnant water, water in marshy areas, or water from ponds that could have been contaminated by wildlife or cattle. They should practice good management of manure (both water and manure can harbor the spirochete), fence in water sources to keep wildlife out, drain wet muddy areas where horses are pastured, and disinfect any areas where infected animals may have been.

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