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Neurological Disease: EPM
(Scientific Name: Equine Protozoal Myeloencephalitis (EPM)


Equine Protozoal Myeloencephalitis (EPM) is an infection of the central nervous system caused by horses ingesting opossum (possum) feces in contaminated feed, pasture or water. The feces are harmful because they often include a parasite that can cause lesions to a horse's spinal cord and brain stem. This neurological damage causes the various symptoms of EPM. 


EPM is considered to be the number one cause of neurological problems in equines today, though Lyme disease can also cause neurologic symptoms. Horses of any age, sex or breed can develop EPM. Those at greater risk for this disease appear to be younger horses and those transported frequently. The risk for contracting EPM also seems higher in the autumn months.


It is believed that more than 50% of all horses in the United States have been exposed to EPM. However, not all horses exposed to the parasite will develop the disease and show clinical signs of EPM. Some equines seem to mount an effective immune response and are able to combat the disease before it gains a foothold. Other horses however, especially those under stress, can succumb rapidly to the debilitating effects of EPM. Still others may harbor the organisms for months or years and then slowly or suddenly develop symptoms. One notable clue is the disease often tends to affect one side or part of the horse more than another.


Common body symptoms include:

» loss of coordination of the rear feet, worse on one side especially moving uphill or downhill and while stopping or raising the head;

» lameness that comes and goes;

» changes to any gait; 

» lethargy;

» muscle atrophy, often over the rump or shoulders;

» hind end weakness - worse on ground that slopes left to right or front to back; 

» problems balancing when hoof is lifted;

» circling, slipping or falling while walking;

» leaning on a stall wall for balance;

» standing with a hoof cocked out or in, not standing square; 

» dragging a hoof, especially while turning;m

» a sore back, changes in the fit of the usual saddle;

» unusual sweating patterns or times;

» carrying the tail to one side or away from the body; 

» lack of sensation or heightened sensitivity in skin or hooves; and

» locking of the stifle joint.

Common head symptoms include:

» a drooping lip or facial twitch;

» change in vision;

» trouble eating or swallowing;

» head tilt;

» drooping ear; and

» changes in behavior, including throwing the rider.


Almost every part of the country has reported cases of EPM, though the incidence of the disease is much lower in the western United States, especially in regions with small opossum populations. However, due to the transport of horses and feedstuffs from one part of the country to another, all horses are at risk.


SYMPTOMS: EPM is a master of disguise. One of the difficulties in diagnosing EPM is that the disease can mimic many other equine health problems.  One obvious symptom is that the disease often tends to affect one side or part of the horse more than another. Symptoms vary between horses and can manifest themselves in mild to severe forms in the body and head.




Prevention is critical in controlling EPM development.  Limiting opossum access to the barn or stable and pasture is the best preventative measure. Opossums are good climbers and may enter the barn over a stall door.  Pick up all cat and dog food




every night and store it in a raccoon/opossum proof container.  Sweep up spilled grain immediately and empty the trash can often.  Keeping food items locked up or out of the barn will make it less tempting for opossums to enter. Trapping and relocating opossums as well as installing appropriate fencing can also help prevent against your equines being exposed to EPM.


The EPM protozoa parasite does not occur in horse manure; so the disorder is not spread between equines. Owners can make a difference by learning effective prevention measures and how to identify EPM symptoms right away. If EPM is diagnosed and treated early, many horses with the disorder respond well to treatment, with a good percentage recovering fully.  


If EPM is suspected, careful veterinary examination, including blood or spinal fluid tests must be done to rule out diseases like West Nile Virus or viral encephalitis. Laboratory testing for EPM is not definitive, though some of the new tests are more accurate than in the past. Once a diagnosis of EPM is established, treatment of the horse should start immediately.  A delay in treatment allows the disease to progress, potentially causing additional permanent damage to the central nervous system.  


Treatment can involve drugs known to kill or retard the reproduction of the responsible protozoa S. neurona.  None of the drugs kill 100% of the protozoa. But the drugs reduce the protozoa population to a level where the horse's immune system kills the rest.  It is important to help the equine rebuild its immune system while treatment is ongoing. Relapses are frequent without strong immune system support. Reduction of stress and a healthy diet are also important. Significant help is also needed through supplementation in supporting the immune system in order to combat this disease.


Treatments can be expensive. Although complications are rare, treatments may affect stallion fertility and may pose certain health risks to unborn foals. While treatment success rates are high, not all equines respond positively to therapy and approximately 10-20% of horses may experience a relapse. Equines that have recovered may still suffer from some permanent damage.


While a horse is being treated, taking intermittent blood samples may be recommended to monitor potential side effects such as anemia, low platelet count and low white blood cell count. Some drugs used to treat EPM are antifolate drugs (drugs which impair the proper folic acid metabolism often producing a folic acid deficiency). Therefore, periodic examination for anemia is recommended during treatment. 


Equines undergoing treatment should also be closely observed for signs of decline, particularly from the negative side effects of the administered drugs, such as acute diarrhea. Be sure to report any changes in the horse’s condition to your veterinarian.


Integrative Medicine


Not all animals can use all natural remedies; allergic reactions to oils
and/or herbs and digestive problems are possible.
A natural remedy is not a substitute for veterinary care.


The following nutraceuticals or natural/herbal formulas can also provide effective treatment and support for equines living with EPM.


In addition to the drugs your veterinarian may administer, there are many alternative therapies to help horses recover from EPM. These include acupuncture, Chinese herbs, chiropractic treatment, massage and vitamin therapy and traditional herbs.


Natural products like herbs can help an EPM horse to recover from the stress it often undergoes during the first three months of conventional treatment, such as heavy drug therapies like sulfa drugs. Herbs can be used during this time for "whole body support" while strengthening the equine’s immune system. Examples of the herbs include:


» Astragalus;

» Siberian Ginseng;

» Feverfew;

» Nettle;

» Yarrow;

» Cleavers;

» Dandelion leaf;

» Calendula; and

» Boneset.


Pau D'arco tree bark has also been found to have anti-protozoan properties as well as being able to boost the immune system. Other herbs such as Milk Thistle and Dandelion help liver function and prevent some of the toxic side effects of the drugs. If the EPM horse is anemic, Chinese blood building herbs can be used in conjunction with the drugs. Always seek your veterinarian's about adding herbal therapy.


Neurological Disorder: EPM

  1. Equine Products –

(Reference: Veterinarians’ Desk Reference)

(Live Link)






2 scoops bid

Source of naturally occurring bioactive proteins–IGG and peptides, modulates gut barrier function and inflammatory cytokine production, and improves immunity.


12-24 capsules sid

Includes the best-researched nutrients for neurological support, providing antioxidant protection for sensitive neuronal tissue.


1 scoop bid

Component of acetylcholine.

Enhance Life14

4 tsp bid

Helps the overall metabolism of older horses, improves weight and energy level.


8-12 capsules sid

Strengthens immune system.


2-5 mL, bid or tid

Corrects intestinal pH; supports intestinal healing during antibiotic use.


4-10 capsules sid

Balanced forms of Vitamin E. No added soy oil (a pro-oxidant). Antioxidant. Vitamin E deficiency can occur with commonly used drugs.

ABC’s EPM Supplement w/o folic acid1

1 scoop sid

Contains Vitamin E, Choline, antioxidants for nervous system support.


6-10 mL sid
Adapt to stress.

Adaptogenic herbs, support the immune system, adrenals, reduces stress, helps horses

Qing Hao San3

2 scoops bid

Tonifies Qi, kills parasites, strengthens nervous system.


To help you quickly find the right Integrative Medicine formulas and manufacturers to help treat your dogs, cats and horses, please refer to the Veterinarians’ Desk Reference
(Click Here)



(Always consult with your veterinarian to properly diagnose any health problems. Misdiagnosis and/or mistreatment -- including OTC and/or homeopathic products -- can lead to dangerous complications.)



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