What is EPM in a Horse: Understanding Symptoms, Treatment, and Prevention

how do horses get epm

Equine Protozoal Myeloencephalitis (EPM) is a potentially fatal neurological disease that affects horses. It is caused by a protozoan parasite known as Sarcocystis neurona, which infects the central nervous system of the horse. The disease can cause damage to the spinal cord and brain, leading to a range of symptoms that can be difficult to diagnose and treat. EPM is a serious concern for horse owners and veterinarians, and early detection and treatment are crucial for the horse’s recovery.

What is Equine Protozoal Myeloencephalitis?

Equine Protozoal Myeloencephalitis is a neurological disease that affects horses. It is caused by the protozoan parasite Sarcocystis neurona, which is carried by opossums and shed in their feces. Horses become infected when they ingest the parasite, usually by grazing on contaminated pasture or drinking contaminated water. Once inside the horse’s body, the parasite travels to the central nervous system, where it can cause damage to the spinal cord and brain.

What Does EPM do to Horses?

EPM can cause a range of neurological symptoms in horses, which can vary in severity depending on the extent of the damage to the nervous system. Some horses may exhibit only mild symptoms, while others may become severely disabled or even die from the disease. The parasite damages the myelin sheath that covers the nerve fibers, leading to inflammation and dysfunction in the nervous system. This can cause a range of symptoms, including:

  1. Ataxia: A horse with EPM may have difficulty walking or standing, and may appear uncoordinated or wobbly.
  2. Muscle wasting: EPM can cause muscle weakness and wasting, particularly in the hindquarters.
  3. Weakness: Horses with EPM may become weak and lethargic, and may have difficulty getting up or lying down.
  4. Abnormal gait: Horses with EPM may have an abnormal gait, with a short stride or a “stiff” walk.
  5. Head tilt: Some horses with EPM may tilt their head to one side or have difficulty holding their head up.
  6. Seizures: In severe cases, EPM can cause seizures or other neurological disturbances.
  7. Sensitivity to touch: Horses with EPM may be sensitive to touch or pressure in certain areas of the body.
  8. Behavioral changes: EPM can cause changes in a horse’s behavior, such as depression or irritability.

It is important to note that not all horses with EPM will exhibit all of these symptoms, and some horses may have only mild symptoms that are difficult to detect. Additionally, the symptoms may come and go or worsen over time.

Equine Protozoal Myeloencephalitis Treatment

Early detection and treatment of EPM are crucial for the horse’s recovery. If EPM is suspected, the horse should be examined by a veterinarian, who may perform a neurological exam and other diagnostic tests, such as a spinal tap or blood test, to confirm the diagnosis. Treatment typically involves a combination of medications, including anti-inflammatory drugs, antibiotics, and antiprotozoal drugs, which are designed to kill the parasite.

It is important to note that not all horses with EPM will respond to treatment, and some may require long-term therapy to manage the symptoms of the disease. Additionally, horses that have been treated for EPM may be more susceptible to reinfection, so it is important to take steps to prevent future exposure to the parasite.

Preventing Equine Protozoal Myeloencephalitis

Preventing EPM in horses can be challenging, as the parasite that causes the disease is widespread and can be difficult to detect. However, there are some steps that horse owners can take to reduce the risk of infection, including:

  • Keeping pastures clean: Remove manure and other debris from pastures regularly to reduce the risk of contamination.
  • Feeding hay from clean sources: Avoid feeding hay that has been stored in areas where opossums or other animals may have defecated.
  • Keeping feed and water sources clean: Keep feed and water sources clean and free from contamination.
  • Preventing contact with opossums: Keep opossums out of barns and pastures by using fencing and other barriers.
  • Monitoring horses for symptoms: Keep a close eye on your horse’s behavior and gait, and report any changes to your veterinarian right away.


EPM is a serious disease that can have a significant impact on a horse’s health and well-being. Early detection and prompt treatment are essential for a successful recovery. By working closely with a veterinarian and taking steps to prevent infection, horse owners can help to protect their animals from this debilitating disease.

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