Lyme Disease in the Equine

Posted by Joyce Harman, DVM on Aug 18th 2022

Lyme Disease in the Equine

Lyme disease (LD) has been recognized for about 40 to 50 years. It is now the most commonly reported tick-borne illness in the United States and Europe and it is found in Asia and Australia. Since LD can be found in so many locations, it should be considered as part of a rule out list when a diagnosis is not clear.

The Organism

The Lyme spirochete (Borrelia burgdorferi) is a mobile, corkscrew-shaped bacteria. The life cycle involves the deer tick or black-legged tick in the East Coast region, with other tick species involved in other places. Contrary to popular belief, deer are not the only host for the infected tick as the different tick species prefer different hosts. Many small mammals are part of the host cycle, from the white-footed mouse (the main one in the Northeast) to the chipmunk, hedgehog, squirrels and rats, along with humans and dogs. Fleas, spiders, mosquitoes and mites are also possible parts of the life cycle, although the available research has not defined their exact role.

The tiny nymph stage ticks are the source of most infections while the adult tick, which is a little larger and easier to see, may be less important but potentially infective.

The difficulty with this organism is that it is incredibly smart (talks to other spirochetes) and adaptable. It can change shape and evade the immune system, as well as become dormant waiting for an opportunity to reactivate. It has outer surface protein coats, called Osp, which change as the tick attaches and begins to suck the host’s blood. This and many other adaptations allow it to become resistant to antibiotics, herbs and the host’s immune system.

Symptoms and Diagnosis

The characteristic “bull’s eye” skin lesion is not seen, most likely due to the hair coat. One of the most common signs is lameness or arthritis that is difficult to identify and may change locations. Other symptoms are anterior uveitis, neurologic signs, low grade fever, sensitivity to touch, lameness, weight loss, tremors, neck pain, lethargy and laminitis. The key is that there is usually some degree of behavior change.

About 10 to 15 percent of the horses in my practice area become dangerously spooky when infected with LD. The exact reason for this is unknown but it may be due to one of the different strains. Sometimes LD appears along with or before or after cases of equine protozoal myelitis (EPM) particularly in older horses. Sometimes LD presents with neurological symptoms that look like EPM, but are negative to the EPM test, and positive for LD.


The issue of co-infections with other organisms is a serious problem and complicating factor with humans. True co-infections have not been identified in the equine, however the concept cannot be ruled out. In my experience, cases of EPM occur along with LD, particularly in older horses.

Bartonella is one of the common human co-infections. It has been identified in the equine, and potentially implicated in several diseases. It is difficult to culture, so it is currently not able to be reliably diagnosed, or treated with conventional means.

Laboratory Diagnosis

Laboratory diagnosis of LD can be difficult, partly due to the cleverness and changeability of the spirochete, and partly because the tests are not good enough yet. The main test is performed by Cornell University, called the Lyme Disease Multiplex Test. This test measures different stages of the disease but it still does not correlate well with the clinical signs. The test can be negative, yet a horse can still respond to treatment and behave like it has LD.


There is no magic bullet in treating chronic LD cases. The best approach is a multi-systemic one, using a combination of conventional, complementary and alternative medicine. Successful treatment of LD includes support for the immune system, not just during the immediate treatment period, but over the long term. Due to the LD spirochete’s ability to “recur,” the immune system must be prepared to respond at a moment’s notice.


Antibiotics are useful especially in the freshly diagnosed horses. Repeated bouts of antibiotics or use for two to three months or more usually produces resistance and is detrimental. It is better to change to herbs and keep the spirochete guessing. The use of antibiotics does suppress the immune system in the gut, so the rest of the plan needs to support it.

Herbal Treatments

The microbiome is the DNA of the microbes living in the gut. Probiotics are an absolute necessity in treating LD and should continue to be fed for many months after antibiotic therapy is finished. The purpose of the long term feeding of probiotics is to restore the health of the microbiome and the immune system.

For herbal treatments to remain effective over the long period of time it takes to treat LD formulas need to be rotated. The spirochete can adapt to any therapy repeated for too long.. Usually with horses a monthly rotation to a new formula seems to work well. Background immune supporting compounds can be used for a long time, the herbs to be changing are those involved with the spirochete.

Noni, (Morinda citrifolia), is an herb that supports the immune system and has excellent anti-inflammatory properties. In the fruit leather form, it is relatively inexpensive and concentrated, while the juice form can be expensive, more dilute and contains a significant amount of sugar.

Omega-3 fatty acids are anti-inflammatory as well as supportive to the immune system. They can be obtained through feeding whole flaxseed (inexpensive), naturally stabilized ground flax, hemp seeds or Chia seeds (a stable omega-3 source). Flax or hemp oils can be used; however, they must be refrigerated during warm or hot weather. Three to six ounces twice a day is the usual dose for seeds; less volume is used with the oils. Blue-green algae also contain significant amounts of omega-3 fatty acids.

Medicinal mushrooms are useful for their positive effects on the immune system and benefits in various arthritic conditions. They are safe and can be used over a long term in a tincture or powder. The mushrooms most useful in treating LD are Cordyceps (Cordyceps sinensis), Reishi (Ganoderma lucidum), Shiitake (Lentinula edodes) and Turkey Tail (Trametes versicolor).

Herbs that have been used in horses successfully are many of the same ones used in human formulations. Andrographis paniculata, sarsaparilla, Pau d'arco, teasel, ashwagandha, Houttuynia leaf, garlic and many more are similar. Supporting herbs for the arthritic pain, stiffness and lethargy can be added, such as Siberian ginseng, echinacea, milk thistle, meadowsweet and ginger.

Clinically, cat’s claw has been less effective in horses than in humans, except for some individual cases. It's possible the dosing needs to be different, or it's possible that it may not be as effective in horses.

Japanese knotweed contains high levels of resveratrol that have been used in humans for treating LD successfully. It seems to be useful in horses, with its strong immune support, and its anti-infective properties.

Chinese Medicine

From a Chinese perspective, LD presents as a wind condition usually in the beginning, progressing to liver Qi, blood stagnation (where you see the pain, irritability). Later stages can progress to blood stasis, Qi stagnation and persistent pain. Qi deficiency (lethargy) is common at all stages. Herbs (and acupuncture) can be selected based on the pattern that presents. This pattern can change as the horse moves through treatment, or seasonally along with the weather.

General Herbal Support

Herbs to support general gut health can be beneficial, especially after prolonged courses of antibiotics. Marshmallow leaf, and meadowsweet are examples. Turmeric root is an herb that shows excellent anti-inflammatory effects on joints and supportive properties to the liver. Garlic may be beneficial; it may also help keep some ticks away and is a good tonic herb.

Essential oils

Research is beginning to show improvement with essential oils. This spring will be the first year to try using them with the horses.


The use of hemp with cannabinoids (CBD) for LD in horses is new, but clinical use is showing excellent results. In humans, CBDs are being used in LD successfully. The effects of cannabinoids on the immune system, arthritis, pain relief, and for their help with inflammation are some of the reasons they are useful in LD.

CBD is usually available as an oil extract. This is an expensive way to give it to horses, since the dose that seems to have the best clinical effect is about 25 mg twice a day. Poor quality CBD is a common problem and products with a low concertation likely have less effect. Hemp is a weed that will grow anywhere, and will extract toxins from the soil, so it's important to use organic, traceable products. Recently a powdered hemp extract on the leaf is being used.

Other support

Vitamin C is well known for its action in the immune system and collagen (four to six grams twice a day). Coenzyme Q-10 is a fat-soluble antioxidant that may be beneficial. Resveratrol is another antioxidant that can be used in LD cases. Colostrum from grass-fed cattle is an excellent Qi tonic (Chinese medicine) and immune system support.

Joint supplements are important for any horse that has shown signs of joint-related discomfort. These include glucosamine-based supplements, hyaluronic acid, glycosaminoglycans and green-lipped mussel as well as Western and Chinese herbal preparations.

Exercise at the level the horse is comfortable with is an important part of recovery. It is good for the immune system, and it is helpful for the horse’s mental health. There is no benefit to pushing the horse beyond what is comfortable, so if the horse is having a bad day, a short walk will suffice.

Stress is an important factor in the recovery from LD. Herbs also can be used to help counteract stress. It is beneficial to maintain horses under stress on adaptogenic, stress relieving herbs such as Siberian ginseng root (Eleutherococcus senticosus) once they have recovered and gone back to competition. It is also important to observe the amount of rest the horse gets at a barn. It has been shown that at many busy barns, horses actually get very little rest and sleep. This adds to stress, which suppresses the immune system.


Prevention is difficult if you live in a LD endemic area. Topical antiparasitics are toxic to the animals and the environment (if they are washed off in the rain and get into the waterways). In some cases, it is easier to support the horse’s system to deal with the drugs than to treat chronic LD. In other cases, it is beneficial to use a more natural approach. For example, Guinea hens are effective at removing ticks from the environment, although they are noisy and may not fit with the farm environment. Keeping the grass mowed in the pasture is also helpful.

Topical essential oils and various insect repellant sprays can be helpful but need to be applied frequently. Japanese knotweed root appears to be helpful in endemic areas but cannot be said to guarantee protection. A new topical spray (Ticks-Off®) is available which prevents the ticks from adhering to the hair. This is an exciting addition to the prevention protocols. It is non-toxic and therefore safe to add to a prevention program. Feeding garlic or apple cider vinegar can be helpful.