Leptospirosis is a disease caused by a Leptospira bacteria; there are approximately 21 species divided into groups based on their propensity for causing disease. Because the organisms survive in surface waters (such as swamps, streams, and rivers) for extended periods, the disease is often waterborne.
Horses may contract leptospirosis by direct contact with infected urine or urine-contaminated feed or water. Less commonly, transmission of the bacteria may occur via bite wounds, eating infected tissue, or during birth. Once in the body, leptospires spread rapidly via the lymph system to the bloodstream and then to all tissues. If the animal mounts an immune response and survives, leptospires will be cleared from most organs and the bloodstream. However, the infection persists in sites hidden from the immune system; the most common hidden site is the kidneys. Persistence in the kidneys results in a carrier state. An infected animal may shed leptospires in the urine for at least a year.
Leptospirosis in horses is most commonly associated with inflammation of the inner part of the eye (also called uveitis or periodic ophthalmia) or abortions. The disease is typically seen as a mild fever with loss of appetite, although severe forms can cause the presence of free hemoglobin in the urine, low blood counts, jaundice, depression, and weakness. Kidney failure has been seen in affected foals.
Recurrent uveitis, or moon blindness, develops any time from 2 to 8 months after the initial infection. Leptospirosis appears to be a significant cause of recurrent uveitis in horses, accounting for up to 67% of the cases. Leptospirosis is responsible for 3 to 4% of all equine abortions annually, although flooding and other environmental catastrophes may result in abortion outbreaks.
Your veterinarian will likely recommend antibiotics for leptospirosis. Uveitis is treated as needed to reduce the inflammation and prevent adhesion of the iris to the cornea or the lens of the eye. No vaccine is currently available for horses. People are susceptible to infection with some of the species of Leptospira. Laboratory tests are necessary for a definitive diagnosis.
Also see our professional content regarding leptospirosis in horses.