Lyme Disease in Horses: Tick Exposure, Symptoms, and Testing

Lyme disease is an infection caused by the bacterium Borrelia burgdorferi. In horses, it is spread through the bite of infected blacklegged ticks, often called deer ticks. Exposure is common in some parts of the United States, especially in wooded or brushy areas where ticks thrive.

One tricky part is that exposure is not the same as illness. Many horses develop antibodies after tick bites and never show clear clinical disease. That means a positive test can tell your vet that your horse has been exposed, but it does not automatically prove Lyme disease is the cause of current symptoms.

When horses do become clinically affected, signs can be vague and overlap with many other conditions. Your horse may seem stiff, sore, less willing to work, or unusually sensitive to touch. In less common cases, Lyme disease has been associated with neurologic signs or eye inflammation, which is why a full veterinary workup matters.

Lyme disease in horses is caused by infection with Borrelia burgdorferi, a bacterium carried by infected blacklegged ticks. Horses are exposed when ticks attach and feed long enough to transmit the organism. Risk tends to be higher in regions where Lyme disease is established and in environments with woods, leaf litter, tall grass, brush, and abundant wildlife hosts.

A horse does not get Lyme disease directly from another horse. The infection depends on tick exposure. Because ticks can be tiny and easy to miss, pet parents may never see the bite that started the problem.

Not every exposed horse becomes ill. In fact, seropositivity is common in some areas, which means many healthy horses have antibodies from prior exposure. That is why your vet looks at the whole picture: where your horse lives, whether ticks are common on the property, what symptoms are present, and whether another condition could explain the signs better.

Diagnosing Lyme disease in horses can be frustrating because there is no single test that proves active disease in every case. Your vet usually starts with a physical exam, a careful history, and discussion of tick exposure risk. Blood testing for antibodies is common, but positive results often reflect exposure rather than illness.

In many horses, your vet may use serology as one piece of the puzzle. Cornell's Equine Lyme Multiplex is one example of a quantitative antibody test used to help interpret stage of exposure and monitor trends over time. Your vet may also recommend a complete blood count, chemistry panel, lameness evaluation, neurologic exam, or other testing to rule out conditions that can look similar.

In selected cases, PCR or testing of affected tissues or fluids may be considered, but these are not routine screening tools for every horse. Because some horses stay seropositive even after treatment, follow-up is often based more on clinical improvement than on making the antibody number go to zero. A diagnosis is strongest when compatible signs, exposure history, and test interpretation all line up.

Prevention focuses on reducing tick exposure. Check your horse regularly, especially around the mane, tail, ears, jawline, between the legs, and under tack areas. Prompt tick removal matters. Your vet can also help you choose horse-safe tick control products or management strategies that fit your region and your horse's lifestyle.

Pasture and property management can lower risk. Mow high grass, reduce brush and leaf litter near turnout areas, and limit access to wooded edges when possible. Wildlife management is not always easy, but reducing habitat that attracts deer and rodents may help decrease tick pressure over time.

Because many healthy horses in endemic areas test positive, routine screening of symptom-free horses is not always helpful. A more practical plan is to work with your vet on seasonal tick prevention, regular hands-on checks, and early evaluation if your horse develops stiffness, shifting lameness, touch sensitivity, or unexplained performance changes.