Equine protozoal myeloencephalitis (EPM) is a central nervous system (CNS) disease of horses that can be caused by either of the protozoa Sarcocystis neurona or Neospora hughesi,¹ although the majority of cases are caused by the former. EPM can result in devastating neurologic disease, and a small percentage of exposed horses will develop EPM after ingesting feed or water contaminated with the protozoa.

EPM has been reported in most of the contiguous 48 states of the USA, southern Canada, Mexico, and several countries in Central and South America. In North America, the definitive host for S. neurona is the opossum (Didelphis virginiana). These animals will eat or scavenge nearly anything, and become infected by eating sarcocyst-containing muscle tissue from an infected intermediate host. Thereafter, infectious sporocysts are passed in the opossum’s feces and subsequently infect horses. 

Infection with S. neurona can also cause neuromuscular disease that does not result in destruction of neurological tissues, and this condition is more readily treatable. Diagnosis and treatment of EPM require that the veterinarian distinguish between EPM and non-brain associated S. neurona infections (sarcocystosis).²

Symptoms of EPM in the Horse

Since EPM is a disease of the central nervous system, it can affect multiple locations within the brain and spinal cord. Therefore, the signs and severity of EPM can vary widely. While EPM can affect both the brain and spinal cord, it is more common for symptoms to be associated with damage to the spinal cord.¹

Many equine veterinarians refer to “the 3 A’s” when evaluating symptoms of EPM: Asymmetry, Ataxia and Atrophy. 

1.     Asymmetry describes symptoms that are worse on one side of the body than on the opposite side. 
2.     Ataxia references incoordination or the inability of the horse to know exactly where its legs are.
3.     Atrophy is a condition where the muscles shrink from their normal size due to lack of use or neurological stimulation. 

EPM Treatment and Folic Acid Deficiency

While EPM is not curable, it can be managed if diagnosed early. Recommended treatments include anticoccidial drugs such as ponazuril, diclazuril, sulfadiazine and pyrimethamine. Other treatments may also be provided based on the severity of the clinical signs. NSAIDs such as phenylbutazone or banamine are occasionally administered to more severely affected horses during antiprotozoal treatment in an effort to prevent worsening of neurological effects.^1,2

Folic Acid (also known as folate or Vitamin B9) is a water-soluble vitamin that is involved in DNA synthesis, methionine production and cellular growth and development. Many of the drugs used to treat EPM in horses (e.g., sulphadiazine, pyrimethamine, diclazuril, toltrazuril) interfere with folic acid metabolism, which is essential for the survival of the causative protozoan S. neurona. Unfortunately, they can also lead to a deficiency in folic acid, which is necessary for the horse in mounting an effective immune response to the protozoa.² Therefore, folic acid supplementation is often recommended when treating EPM.

Folic acid is used to treat folic acid deficiency in dogs, cats, horses, and other animal species, which is often caused by small intestinal inflammatory disease, chronic administration of dihydrofolate reductase inhibitor drugs, or dietary deficiency. It is important for supporting cell turnover during periods of rapid growth such as fetal development, tissue repair, and regeneration of cells lining the intestinal wall. Folic acid is sometimes given to horses to improve hemoglobin levels because of its role in maintaining healthy red blood cells.²

Where to buy Folic acid

Folic acid is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies.

Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Equus Magazine.

²ucdavis.edu.