The Symptoms & Diagnosis of Lyme Disease in the Equine

By Dr Joyce Harman DVM, MRCVS


The characteristic bull’s-eye skin lesion is generally missing in the equine and dog, most likely due to the presence of their hair coat. One of the most common signs is lameness that is difficult to specifically identify. In humans, cognitive problems, irritability, fatigue, headaches, disorganization, nerve pain, deficits in memory and retrieval of information, reduced perceptual motor skills, and problem solving are all serious issues. All of these symptoms likely exist in the horse though we usually see irritability, fatigue, lack of interest in work, perhaps stubbornness, or perceived stubbornness, or dullness, all of which are difficult to diagnose. Clinically, about 10-15% of the horses in the author’s practice area become dangerously spooky when infected with the Lyme spirochete


A combination of a thorough history along with a complete physical exam and blood work are required. The history often becomes the most important part of the diagnosis. Many, if not most, of the horses show behavioral changes of various sorts, the most common being lethargy, irritability, or lack of interest in their surroundings. In some cases, as mentioned above, the behavioral changes trend more towards the hyperactive or spooky side. The key is a significant mental change.

The physical part of the history can include shifting leg lameness, stiffness, joint swelling, poor performance, reluctance to turn, and poor jumping performance, etc. In many cases, horses have been worked up for subtle lamenesses and have had traditional treatments such as joint injections and various anti-inflammatory medications but have not responded well. Diagnostic imaging may be inconclusive or may point to joint inflammation, yet treatment of that inflammation yields poor results.

Other signs that have been attributed to Lyme borreliosis are anterior uveitis, neurologic signs, low grade fever, sensitivity to touch, lameness, weight loss, tremors, neck pain, lethargy and laminitis. These signs can be caused by other diseases that are also commonly seen. Those include anaplasmosis, EPM, “tying up,” equine polysaccharide storage myopathy, and many more.

Laboratory diagnosis

Laboratory diagnosis of LD can be very difficult, even with humans where testing is significantly more sophisticated. This is in part due to the cleverness and changeability of the spirochete, and partly because the tests are not good enough yet. With the equine, the main test is performed by the Cornell University College of Veterinary Medicine Animal Health Diagnostic Laboratory Center and is called the Lyme Disease Multiplex Testing for Horses. This quantitative test measures the 3 different antigen proteins on the outer surface of the spirochete, the Osp A, C, F. OspA is for vaccination responses; however, this author has seen it be positive in known unvaccinated horses. OspC is for the early infection and F for the chronic cases. However, it may be that the horse has both an acute and a chronic infection, so the test is still not absolute. Horses with long-term chronic infections also may have a poor immune response, so the test numbers may not correlate with the severity of the infection in this author’s experience.

The other test used is the Idexx SNAP test, which has the advantage that it can be performed at the horse’s side. This reads surface antigens that mark viable spirochetes. The C6 antibody declines rapidly after treatment (since the spirochete can go inside the cells).  Snap 4Dx  testing yields some false positive and false negative results, and does not give a quantitative result. It is useful for screening purposes, but should be followed up with the quantitative test to obtain a better understanding of the response of the immune system and to be able to compare results from pre-and post-treatment.

Holistic diagnosis

Since LD has many manifestations, there is not one clear-cut pattern observed from a holistic perspective. The practitioner’s training and experience will guide the tools to be used diagnostically and for treatment.

From a homeopathic perspective one needs to take a complete history and prescribe a constitutional medicine based on the animal’s presentation. A good follow-up is important since these cases can be complex. The client also needs to understand that a single homeopathic medicine may not be enough.

From a Chinese perspective, the liver is the most often affected meridian directly and indirectly by the spirochete. Many horses will exhibit signs of liver dysfunction; however, there is seldom one pattern for all horses. Wind invasion is common, and many symptoms are related to that, with shifting signs. There may be Liver Qi Stagnation, Liver Heat rising, Liver Yin deficiency, Liver Blood deficiency, and so on. Frequently a generalized Qi deficiency will be seen. These may be combined with other patterns, often made more complex by long-term drug use.

The key is to approach each case as an individual, from the practitioner’s perspective and experience, and treat that horse’s specific presentation. It may change from month-to-month as well as from year-to-year.

Source: Dr Joyce Harman DVM, MRCVS


In the next blog we will explain the different treaments for Lyme Disease in the Equine - Keep a close eye out for it!