Lyme disease is caused by the bite of an ixodes scapularis tick (also called a black-legged tick or deer tick) carrying Borrelia burgdorferi (B. burgdorferi). More than 476,000 people in the United States are diagnosed and treated for this bacterial infection each year. Beyond North America, Lyme is also found in many countries throughout the world. Humans are not the only ones at risk for Lyme and other tick-borne diseases. Animals like dogs, cats, and horses can be bitten by ticks. If you are a horse owner, you are probably wondering about the possibility of your horse contracting Lyme disease, and what to do if your horse shows clinical signs of Lyme borreliosis. Let’s go through some important information about Lyme disease in horses.
Can Horses Contract Lyme Disease?
Yes. Not all ticks are infected with Borrelia burgdorferi or other pathogens, so not every tick bite will lead to Lyme or other tick-borne diseases. However, Lyme disease is becoming more and more prevalent, not just in previously well-known endemic areas like New England, but in every state in the U.S. except Hawaii and in many places around the world. Ticks live in moist, shady areas like tall grasses and wooded or bushy areas. Horses come into contact with more ticks due to the nature of their living environment, so it is important to know what signs of Lyme disease to look for in your horse and what the treatment is for an infected horse.
Lyme Disease Symptoms in Horses
A lot of horses bitten by an infected tick are completely asymptomatic, so you may not realize that your otherwise healthy horse has Lyme disease. However, there are a few documented symptoms of equine Lyme disease. Lyme disease may affect a horse’s body in the following ways:
- Swollen lump at site of tick bite
- Swollen joints
- Eye inflammation (Uveitis)
- Neuroborreliosis (neurological Lyme disease)
Other possible symptoms may include:
- Sporadic lameness or shifting leg lameness
- Lethargy
- Stiffness
- Muscle tenderness
- Arthritis
- Behavioral changes
- Low grade fever
- Poor performance
If your horse has neuroborreliosis, meaning the Lyme disease infection has spread to the horse’s nervous system, neurological signs and symptoms can include:
- Muscle wasting
- Depression
- Dysphagia (difficulty swallowing)
- Head tilt
- Encephalitis
- Difficult eating
- Chronic weight loss
- Skin sensitivity (tactile hyper-aesthesis)
- Fever
How Do You Test a Horse for Lyme Disease?
Borrelia burgdorferi infection can be hard to diagnose because horses can be asymptomatic, and also because the documented symptoms are common for other illnesses. An equine veterinarian will first try to rule out other common causes for the horse’s symptoms. If they don’t find other another cause for the horse’s symptoms, they can do a blood test for Lyme disease. The test is an enzyme-linked immunosorbent assay (ELISA) followed by a Western blot or immunofluorescence assay (IFA).
Just like human blood tests for Lyme disease, the equine test only looks for antibodies against the Lyme disease bacteria, not for the bacteria itself. A horse’s immune response to Lyme disease can affect whether antibody levels are high enough to show up on a test, so the horse might not get a positive result even if they do have Lyme disease. It usually takes five to twelve weeks after infection for antibodies to show up on a horse’s blood test. There is an Equine Lyme Multiplex Assay offered through the Animal Health Diagnostic Center at Cornell University that can identify antibodies three to five weeks after infection.
Because of the difficulties with testing, veterinarians should also consider a horse’s symptoms as well as their exposure to ticks when making a Lyme disease diagnosis.
How Do You Treat Lyme Disease in Horses?
Lyme disease in horses is treated with antibiotics, either oral doxycycline or minocycline or intravenous oxytetracycline. Treatment is usually for four to eight weeks. Treatment success is based on improved clinical signs as well as a decrease in antibody titers. If a horse has antibiotic resistance or is still showing symptoms after treatment, a veterinarian should evaluate whether there is another problem at bay (such as an inflammatory issue that can be masked by antibiotic treatment that has anti-inflammatory properties) or whether more antibiotic treatment is warranted. Usually, one round of treatment is enough and a horse won’t have long-term effects, but rarely, a horse’s Lyme disease can relapse.
Lyme Disease Prevention in Horses
There is no vaccine for Lyme disease in horses. The best way to avoid contracting Lyme disease is prevention. Horses are often in a pasture or outside for a large portion of their life, so prevention can be more difficult. One method of disease control is to control the horse’s environment so that they are not near areas where ticks like to live. This means avoiding or removing wooded areas, low lying brush, long grasses and weeds, and debris in the pastures. If you limit the areas that ticks like to hide in, then you can limit tick population and, subsequently, your horse’s exposure.
Two other ways to prevent Lyme disease in horses are:
- Tick repellent: Use an EPA-approved repellent on your horse such as DEET or picaridin
- Grooming: Prevent ticks from transmitting Lyme by brushing your horse constantly.
- Do tick checks: While grooming, run your hands over the horse’s entire body, including the ears, tail and tailhead, to feel for small bumps. Carefully remove any ticks using a tweezer or tick tool. Be sure to wear gloves so the tick doesn’t bite you.
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The above material is provided for information purposes only. The material (a) is not nor should be considered, or used as a substitute for, medical advice, diagnosis, or treatment, nor (b) does it necessarily represent endorsement by or an official position of Global Lyme Alliance, Inc. or any of its directors, officers, advisors or volunteers. Advice on the testing, treatment or care of an individual patient should be obtained through consultation with a physician who has examined that patient or is familiar with that patient’s medical history.
