Introduction: Leptospirosis can cause a variety of problems including red blood cell destruction, kidney disease, and abortions. Because this organism thrives in wet environments, infections usually occur when animals have access to marshy areas, ponds, streams, and stagnant surface water.
Causative Agent: Leptospirosis is caused by a spiral-shaped bacterium known as a spirochete. There are many strains of Leptospira, and most equine cases are caused by Leptospira australis, L. pomona, L. hebdomadis, and L. icterohemorrhagiae.
Clinical Signs: Clinical signs vary depending on factors such as age and health of the animal, environmental conditions, and which strain (serovar) of leptospirosis is involved. Generally, the signs in horses include fever, going off feed (anorexia), blindness, lethargy, and a yellowness to the white of the eye and gums (icterus). If the horse is pregnant, abortions usually occur 1-3 weeks after clinical signs. Abortions normally occur during the last 7-11 months of the pregnancy. Infections of leptospirosis have been associated with equine recurrent uveitis (ERU). When the organism affects the eyes, the horse may close the eyes (severe blepharospasm) and be sensitive to light (photophobia). The eyes may appear red and swollen with excessive discharge and tearing (lacrimation).
Disease Transmission: Leptospirosis is carried to a susceptible animal by contaminated water, rodents, wildlife, and domesticated animals. Infections occur when the organism contacts the mucosal surfaces (mouth, eyes, nasal passages, etc.) or an injured area on the skin of a susceptible animal. Once an animal is infected, it sheds the bacteria in the urine, semen, vaginal secretions, or in the placenta and fetal tissues. Because of this, care should be taken when handling any urine, tissue, semen, or discharge from a leptospirosis suspect. Studies indicate that horses can shed the organism in the urine for up to 90 days. Leptospirosis is a very hardy organism and can survive in the environment for long periods of time, provided that freezing temperatures do not occur.
Diagnosis: The most common way of knowing whether leptospirosis is the cause of disease is to run a test called serology. This test requires that paired blood samples be taken from the suspect animal. Leptospirosis is difficult to identify in tissue or body fluid samples and difficult to grow in a culture setting. Because of this, leptospirosis is often diagnosed by excluding other diseases which cause disease and abortion problems in horses.
Treatment/Prevention: It has been shown that antibiotics are successful in clearing the disease. Appropriate eye medications should also be given when required.
Unlike cattle and dogs, there is no vaccine currently available for horses. The vaccines for cattle are sometimes used in horses. These vaccines do not protect against all the strains of leptospirosis that may infect horses and they can trigger some serious allergic reactions. As a result, unless there is a severe outbreak, they are generally not recommended.
There is really no way to specifically prevent a leptospirosis infection in horses. The best that can be done is to prevent the situations where leptospirosis can be harbored and spread. For example, fencing potentially contaminated streams and ponds, controlling rodent populations, and making certain that the horses are separated from cattle, pigs, or wildlife are some of the methods used to reduce disease transmission. When a horse is diagnosed as having a leptospirosis infection it should be isolated from other animals and treated with the appropriate antibiotics.
Public Health Concerns: Leptospirosis is a "zoonotic" disease, meaning that people can become infected. Caution should be used around any animal suspected of having leptospirosis. Contaminated urine is highly infectious for people and susceptible animals, especially when this urine contacts mucous membrane surfaces or abrasions and cuts. Latex gloves should be worn when handling infected animals or their urine. Protective goggles and masks should be worn when hosing contaminated areas.