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Lyme Disease in Horses – Eye Problems to Watch out for.

lyme disease in horses uveitis

Recurrent Lyme uveitis in a horse can cause severe visual defects and even blindness.

Earlier this year, researchers in Ithaca published a paper detailing the diagnosis of Borrelia-associated uveitis from Lyme disease in horses, an inflammatory eye condition that can cause significant pain to the animal and result in permanent visual field defects if untreated. Whilst many are still unaware that horses can get Lyme disease, others are all too familiar with the condition as the infection can occur time and again in the same animal, sometimes causing different symptoms every time.

Uveitis in Horses – Is it Lyme Disease?

Priest, et al (2012), noted that clinical manifestations of Lyme disease in horses are often vague and nonspecific when they are observed at all. Problems with a horse’s gait, behavior, reproductive system, and eyes are some of the symptoms of Lyme disease to watch out for but even then it is difficult to isolate the causative bacteria and tests for Lyme disease in horses are often unreliable, especially if a horse is repeatedly infected. In Priest’s research the two horses in question were diagnosed after discovery of Borrelia burgdorferi in the fluid of the eye itself. As there are a number of potential causes of uveitis in horses (and in humans), Lyme disease is not always the first suspicion and inappropriate corticosteroid treatment may commence prior to proper diagnosis, often making things worse as the infection is helped by such action. Serological testing is just one part of the diagnostic process with cytologic assessment, antibody, and PCR testing of ocular fluids warranted in areas where Lyme is endemic.

PCR Testing for Lyme Disease in Horses

Californian Lyme disease researchers, Imai, et al (2011), also looked at two cases of Lyme disease in horses with vision problems. These cases were chronic and associated with progressive neurological disease in the animals, one of whom was diagnosed with meningoradiculoneuritis. PCR testing was used to diagnose the condition in one of the horses, testing fluid from the inflamed tissues including the spinal cord, muscle, and joint capsule. A specific strain of Borrelia burgdorferi (297) was sequenced, and this matched a previous cases of neuroborreliosis in a human patient. Once diagnosis was made the horses were able to be treated with antibiotics but for some animals this comes too late and long-lasting damage is done to the eyes and other tissues.

Pasture Management for Lyme Disease Prevention

Good pasture management is one of the main ways to prevent Lyme disease in horses with an emphasis placed on keeping grass short, as well as maintaining wide paths between areas of overgrown land and pasture. Ticks tend not to dwell in grassy areas where they cannot hide from the sun and prefer waiting in long grass for passing animals which they then latch on to for a meal. It is important to remember that ticks also carry a variety of other infectious agents, including Babesia, Rickettsia and a newly uncovered viral agent.

Other Symptoms of Lyme Disease in Horses

Neurological abnormalities in horses with Lyme disease are not always easy to interpret as consequences of the infection. Sudden mood changes, grouchiness, hypersensitivity, or a reluctance to be handled, groomed, or ridden can all indicate a medical issue in a previous happy and approachable horse. Signs of encephalitis, such as circular walking, blindness, and pressing the head against a wall can all point to Lyme disease, as can ‘moon blindness’ and an inability to reproduce (a problem for those looking to breed horses who live in a Lyme endemic area).

Preventing Lyme Disease in Horses

Respiratory problems may also be a sign of Lyme disease and some horse-owners ensure that their animals have their titers tested annually, or more often, to make sure they catch Lyme disease promptly. Treatment with antibiotics prior to actual diagnosis with Lyme disease is also becoming more popular but this poses the risk of creating antibiotic-resistant superbugs, as well as affecting the horse’s gastrointestinal system, liver, and general health.

Vaccinating Horses Against Lyme Disease

Vaccinating horses against Lyme disease is also an option, as with dogs, but there are safety concerns over the use of such vaccines including a suspicion that kidney problems may be connected to the vaccinations. Another major concern is simply that vaccination against Lyme disease can complicate diagnosis should infection actually occur. This is because titers may be high due to vaccination and infection, making it hard for the veterinarian to determine if an active infection is present. Serological tests alone are usually insufficient to diagnose Lyme disease in horses but those with ocular manifestations of Lyme disease may have the infection confirmed by testing fluid from the eye itself.


Priest HL, Irby NL, Schlafer DH, Divers TJ, Wagner B, Glaser AL, Chang YF, Smith MC., Diagnosis of Borrelia-associated uveitis in two horses. Vet Ophthalmol. 2012 Feb 23.

Imai DM, Barr BC, Daft B, Bertone JJ, Feng S, Hodzic E, Johnston JM, Olsen KJ, Barthold SW., Lyme neuroborreliosis in 2 horses. Vet Pathol. 2011 Nov;48(6):1151-7. Epub 2011 Feb 1.

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