Equine protozoal myeloencephalitis (EPM) is caused by infection of the central nervous system with the protozoan parasites Sarcocystis neurona and in some instances, Neospora hughesi. It is a progressive, debilitating disease in horses that can affect any part of the nervous system. EPM is considered the most prevalent cause of neurologic disease of horses in the Americas. The opossum is the definitive host of S. neurona; its habitats reflect the geographic range of EPM in horses. Opossums shed the sporocysts in their feces, and horses become infected by ingesting food or water that has been contaminated with opossum feces. In areas in which the opossum is prevalent, approximately 50% of horses will be seropositive for S. neurona.1

Clinical signs of EPM are generally dependent on the area of the central nervous system that contains the parasite, as well as the type of damage that has been caused. The onset of EPM may be slow or sudden, and the clinical signs are often asymmetrical.

The symptoms of EPM can include:

• Ataxia (incoordination), abnormal gait or lameness

• Progressive weakness

• Muscle atrophy (more severe along the topline or in the large muscles of the hindquarters)

• Paralysis of muscles of the eyes, face or mouth, evident by drooping eyes, ears or lips

• Difficulty swallowing

• Seizures or collapse

• Abnormal sweating

• Head tilt with poor balance (the horse may show a splay-footed stance or lean against walls)2

Ponazuril + Vitamin E for the Treatment of EPM in Horses

Ponazuril is an anticoccidial (antiprotozoal) compound with activity against several genera of the phylum Apicomplexa. Ponazuril (also known as toltrazuril sulfone) is a metabolite of the poultry antiprotozoal drug toltrazuril. Ponazuril is a triazine-based drug that acts to inhibit enzyme systems in protozoa and/or decreasing pyrimidine synthesis. Ponazuril is FDA-approved for the treatment of EPM. While great strides have been made throughout the last decade in an effort to understand EPM, many questions remain unanswered concerning its etiology, pathogenesis, occurrence, treatment, and diagnosis. Clinical improvement is noted in 60% to 75% of horses treated with ponazuril, however.2

In addition to anti-protozoal medications, many veterinarians recommend supplementing these with between 5,000-10,000 IU per day of Vitamin E. In animals and humans, vitamin E has been shown to augment the function of the immune system. The literature holds that vitamin E may bolster the immune system to the point where the protozoa are unable to mount a defense against the medications being administered.

Where to buy Ponazuril + Vitamin E

Ponazuril + Vitamin E is available in the U.S. through several 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.

1Reed, S. et. al. Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention. J Vet Intern Med. 2016 Mar-Apr;30(2):491-502.

2Howe DK, MacKay RJ, Reed SM. Equine protozoal myeloencephalitis. Vet Clin North Am Equine Pract. 2014 Dec;30(3):659-75. doi: 10.1016/j.cveq.2014.08.012. Epub 2014 Nov 6. PMID: 25441115.