Leptospirosis in Horses: Abortion, Uveitis, and Kidney Concerns

Leptospirosis is an infection caused by spiral-shaped bacteria in the genus Leptospira. In horses, the disease is most often linked to three major problems: abortion, equine recurrent uveitis (ERU or "moon blindness"), and less commonly acute kidney injury. In North America, Leptospira interrogans serovar Pomona type kennewicki is the strain most often associated with clinical disease in horses.

Horses do not always look dramatically ill when they are first infected. Some have only a mild fever or reduced appetite, then seem to recover. Months later, however, a horse may develop painful eye inflammation, or a pregnant mare may abort. That delayed pattern is one reason leptospirosis can be frustrating for pet parents and breeding farms.

This is also a zoonotic disease, which means people can be exposed from the same contaminated environment and potentially from infected urine or reproductive fluids. If leptospirosis is suspected, your vet may recommend extra handling precautions around urine, aborted tissues, and contaminated bedding.

Horses usually become infected after contact with urine from infected wildlife or livestock, or from water, feed, mud, or bedding contaminated by that urine. Rodents and small mammals are common reservoirs, and exposure risk rises around standing water, flooding, wet pastures, and areas with heavy wildlife traffic.

The bacteria enter through mucous membranes such as the eyes, nose, or mouth, and can also enter through skin wounds. On breeding farms, contaminated birthing fluids and aborted materials may expose other mares if cleanup and isolation are delayed.

Not every exposed horse becomes seriously ill. Some clear the infection with little obvious disease, while others develop pregnancy loss, kidney injury, or chronic eye inflammation. That difference likely reflects timing, immune response, strain involved, and which tissues the bacteria reach.

Your vet usually diagnoses leptospirosis by combining history, exam findings, and laboratory testing. Depending on the case, that may include bloodwork, urinalysis, PCR testing, and antibody testing such as MAT. In horses with abortion or acute renal disease, antibody titers are often more clearly elevated than they are in chronic eye cases.

For abortion cases, testing the placenta, umbilical cord, fetal liver, or fetal kidney is especially helpful. Merck notes that fluorescent antibody testing or immunohistochemistry on these tissues performs very well, and PCR is preferred for fluids such as urine, blood, and ocular samples.

Equine recurrent uveitis can be the hardest form to confirm. Serum titers may be low or even negative because infection may be localized within the eye. In selected cases, your vet or a veterinary ophthalmologist may discuss ocular fluid testing, especially when the diagnosis will change management.

Prevention starts with reducing exposure to contaminated urine and water. Work with your barn team to control rodents, protect feed, clean up spilled grain, and limit access to stagnant water, flooded paddocks, and muddy areas where wildlife or livestock may urinate. Safe water access matters, especially during wet seasons.

On breeding farms, quick isolation and careful cleanup after abortion are important. Your vet may recommend gloves, dedicated tools, and separate handling for mares that abort or horses suspected of shedding the organism. Recently infected horses may shed leptospires in urine for weeks to months, so biosecurity is not only about the sickest-looking horse.

Vaccination is now part of prevention discussions in the United States. AAEP and CDC resources note that horses can be vaccinated against leptospirosis, but no vaccine covers every strain or gives perfect protection. Your vet can help you decide whether vaccination fits your horse's geography, housing, breeding status, and water exposure risk.