Equine protozoal myeloencephalitis (EPM) is a parasitic disease that invades the central nervous system. Horses become infected when they graze in contaminated fields, or eat contaminated food or water.  Typically the progression of EPM is gradual, and an infected horse will show neurological symptoms fairly soon after exposure.

Clinical Signs of EPM
The symptoms and severity of EPM can vary greatly from horse to horse depending upon the location of parasite development and its extent of damage. Sometimes, the parasite infects an animal, but the symptoms will not develop until much later. Some exposed horses never exhibit signs of infection because their immune system responds to fight off the disease. Horses who show neurological symptoms shortly after infection may suffer rapid disease development.

Clinical signs of EPM can range from mild to severe and may include:

• Gait abnormalities
• Stumbling
• Lameness
• Weakness
• Stiffness
• Seizures
• Asymmetric muscle atrophy
• Facial nerve paralysis
• Chewing inabilities
• Swallowing difficulties
• Head tilt
• Vocalizing difficulties
• Abnormal sweating

Treatment for EPM
Treatment for EPM should start once diagnosis is made as the disease will continue to progress and may cause permanent damage.  The drugs used for treatment now are designed to kill or slow the cycle of the parasite, which will allow the horse‘s immune system a chance to rebuild. Some veterinarians may also suggest adding the use of non-steroidal anti-inflammatory drugs, immune system stimulants, and natural Vitamin E to the treatment regimen. It is also recommended to keep the horse‘s stress to a minimum as it heals.

FDA Approved Drugs and Treatment Period

• Pyrimethamine and Sulfadiazine combination
  Minimum of three to six months
  
  
• Ponasuril
  Minimum of 28 days
  
  
• Diclazuril
  Minimum of 28 days      

Prognosis
For the horses that exhibit mild symptoms of EPM and who receive proper veterinarian care, it is estimated that around 80 to 90 percent may recover completely. However, recovery is much more difficult for a horse who exhibits severe symptoms or who receives late or little veterinarian assistance.  Relapses are possible in all recovered horses, regardless of the severity of the case, and routine relapses have been noted on horses who have recovered from severe cases of EPM.  It is not understood why this happens.