Appaloosa grazing in pasture

What is this new disease that my horse can get called lepto?” is a question I’ve been receiving lately while doing farm calls. I begin the conversation by letting clients know that even 20 years ago (20-plus, actually) we studied the bacterium “Lepto” in school, so it is not a “new” disease. Leptospirosis pomona is the agent that can cause abortions, uveitis, kidney disease, and septicemia in horses. It is found in warm, wet environments. In my home state of Florida, about 77% of horses have been exposed to L. pomona. Across the country more than 65% of horses have been exposed.  

Wildlife pass L. pomona via their urine into the environment. So unless your horse lives in a bubble, he’s exposed either in the pasture he grazes or in the hay that he eats. The horse becomes infected by ingesting the bacteria. In the horse, L. pomona resides in the kidneys, then travels via the bloodstream to the eyes or uterus, or it stays in the bloodstream and causes septicemia (systemic infection). In some cases, the bacteria remain in the kidney and cause renal failure.

Who should be worried about leptospirosis in their horses and when? Broodmare owners should be concerned. Some mares have lost foals during pregnancy due to L. pomona infection. It is best to confirm this at the time of the abortion so that current and future pregnant mares on that property can be vaccinated against L. pomona. Veterinarians in Kentucky have seen an increase in abortions during years with higher rainfall. There have also been cases of newborn foals with kidney disease due to leptospirosis. This makes for a financial and emotional burden for horse owners, due to the loss of the foal or the cost of ongoing treatment.

Researchers have found that more than 70% of equine recurrent uveitis (ERU) cases are associated with leptospirosis. Owners of Appaloosas and Warmbloods should be aware that their horses are more prone to leptospirosis-induced ERU than are other breeds. This chronic equine eye problem typically starts as mild inflammation of the eye’s interior. The disease is painful, and treatment is complicated—especially in very tall horses. An owner of an affected horse must treat the animal’s eye for the rest of his life or until he goes blind in that eye; equine recurrent uveitis remains the primary reason horses go blind. Testing of eye fluid and blood samples has shown that about 50% of the time, leptospirosis is the cause for leptospirosis-related blindness.

What signs will I notice when my horse becomes infected? Unfortunately, you may not see any signs until abortion occurs or the eye becomes inflamed. In cases of septicemia or kidney disease, your horse might develop a fever, become lethargic, and refuse to eat. But again, it is difficult to detect L. pomona infection, even if the horse is showing clinical signs of disease. Some clinicians note a fever of unknown origin, with an eye problem developing some time later. But these transient fevers in a horse might go unnoticed by the horse owner.

All the above leptospirosis-related health problems in horses are frustrating to owners and veterinarians. Prevention is the best medicine. A vaccination has been released recently to help those horses that might be prone to L. pomona. The veterinarian administers an initial dose followed by a booster dose three to four weeks later. The horse should then be boostered annually after the initial series. I would recommend that owners of those breeds that are susceptible to ERU vaccinate their horses, and breeders should start off the breeding season by vaccinating their mares. Most of all, talk to your veterinarian, and ask him or her about leptospirosis.