Q: What causes Lyme disease in horses and how is it transmitted?
A: Lyme disease in horses is caused by the bacterium Borrelia burgdorferi, transmitted by blacklegged (deer) ticks that must remain attached for about 18-24 hours.
Q: Which tick species spread Lyme disease to horses in the U.S.?
A: The vectors are Ixodes scapularis in the East and Ixodes pacificus on the Pacific coast, commonly called blacklegged or deer ticks.
Q: Where in North America is Lyme disease risk highest for horses?
A: Endemic areas include the Northeastern, mid-Atlantic, and upper Midwestern U.S., as well as Southeastern Canada.
Q: When are horses at peak risk for Lyme disease exposure?
A: Peak risk is April to October, with climate change extending activity into late fall and even winter months.
Q: How is Lyme disease diagnosed in horses?
A: By detecting antibodies to Borrelia along with clinical signs; tests include serum or CSF, and the Lyme Multiplex assay differentiates new vs. old exposure.
Q: Can standard blood tests distinguish active infection from past exposure?
A: Basic bloodwork cannot, and false negatives can occur if tested too soon; antibodies can persist for years after exposure.
Q: Can a horse be exposed to Borrelia and show no symptoms?
A: Yes, many horses show antibodies without clinical signs and may be completely healthy despite exposure.
Q: Why is Lyme disease difficult to diagnose in horses?
A: Lyme disease has been called “the great imitator.” Symptoms are vague, variable, and mimic other disorders. Diagnosing Lyme disease is often a process-of-elimination effort.
Q: What clinical signs are commonly associated with equine Lyme disease?
A: Signs include low-grade fever, weight loss, lethargy, lameness (shifting), stiffness, muscle soreness, skin sensitivity, behavioral changes and poor performance.
Q: What is Lyme-associated uveitis in horses and why is it serious?
A: Uveitis is an inflammation within the eye that may progress rapidly and can sometimes lead to blindness. Lyme uveitis may also precede the onset of nervous system symptoms.
Q: What neurological complications can occur with equine Lyme disease?
A: Neuroborreliosis can cause behavioral changes, ataxia, neck/back stiffness, fever, sensitivity, respiratory distress, eating difficulty, muscle atrophy, and encephalitis; it can be fatal.
Q: What are the recommended treatments for equine Lyme disease?
A: Treatment with antibiotics lasts 4-8 weeks; a NSAID may also be prescribed.
Q: Should antibiotic treatment continue after initial improvement?
A: Yes, even if signs improve, the bacteria aren’t gone, and untreated damage can be lifelong; relapse is possible.
Q: What prevention measures help reduce tick exposure in horses?
A: Daily grooming, permethrin repellents, pasture management (mow and clear brush to deter deer), along with daily tick checks and prompt, proper removal.
Q: Is there a vaccine for equine Lyme disease?
A: No approved equine vaccine exists; off-label canine vaccines show short-lasting promise but require frequent boosters, and equine protocols aren't established.