Equine protozoal myeloencephalitis (EPM) is a central nervous system (CNS) infection of horses with either of the apicomplexan protozoa Sarcocystis neurona or Neospora hughesi.¹ Most cases of EPM are caused by the S. neuronaprotozoan. Horses become infected by ingesting the S. neurona sporocysts in contaminated feed, grass (while grazing) or water. The definitive host for S. neurona in North America is the opossum (Didelphis virginiana) whose feces are responsible for the contamination and transmission in most cases via sporocysts.

EPM is an extremely serious disease that can cause devastating and lasting neurological damage in the horse and can ultimately prove fatal. It is also very common. In some areas of the U.S., over 90% of horses can be seropositive, meaning that they have been exposed to the S. neurona sporocysts. Horses with antibodies specific to N. hughesi have been found in 21 states and, in some locations, up to 20% of horses may be seropositive to this organism.²  The natural host(s) of N. hughesi have not yet been identified. 

Transplacental protozoal transmission with the birth of infected foals has been documented for N. hughesi but not for S. neurona.¹ Fortunately, most horses are able to mount a sufficient immunological defense and only a very small percentage of horses seropositive to either parasite (around 1%) will develop clinical disease. 

Clinical Signs

Common clinical signs of EPM can include:

• Ataxia (poor coordination)
• Spasticity (stiff movements) 
• Abnormal gait
• Lameness
• Muscle weakness, particularly under exertion
• Muscle atrophy along the topline, or in muscles of the hindquarters
• Facial paralysis
• Difficulty swallowing
• Seizures
• Collapse
• Abnormal sweating.
• Head tilt
• Poor balance
• Leaning against stationary objects

EPM Treatment with Diclazuril + Vitamine E Succinate

Any horse suspected of displaying clinical signs of EPM should be seen by an equine veterinarian immediately. EPM is treated with antiprotozoal drugs and immunomodulators,^3,4 many of which are currently available as compounded veterinary preparations.

Diclazuril exerts its anti-protozoan effect by inhibiting merozoite production. In horses, the oral absorption is 1.56% with a half-life of 43-65 hours. Other studies in horses have shown that at a dose of 1 mg/kg and 0.5 mg/kg the half-life is 55, and 87 hours, respectively, with peak concentration of 0.185 and 0.1 mcg/mL, respectively.⁴

In addition to anti-protozoal medications, many equine veterinarians recommend supplementing these with between 5,000-10,000 IU per day of Vitamin E. Vitamin E succinate (VES) is a succinic acid ester of vitamin E and is one of the most effective anticancer compounds of the vitamin E family. VES inhibits tumor growth by multiple pathways mainly involve tumor proliferation inhibition, apoptosis induction, and metastasis prevention. Its mitochondrial targeting and damaging property provides it with a synergetic effect when used with conventional chemotherapeutic drugs.⁶

Where to buy Diclazuril + Vitamine E Succinate

Diclazuril + Vitamine E is available in the U.S. through veterinary custom compounding companies. 

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

¹Merck Veterinary Manual.

²Reed, S M et al. Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention. Journal of veterinary internal medicine vol. 30,2 (2016): 491-502. doi:10.1111/jvim.13834.

³Dubey, J.P. et. al. (2001). A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM). Veterinary parasitology. 95. 89-131. 10.1016/S0304-4017(00)00384-8.

⁴Mark G. Papich, M. Diclazuril: Pharmacology and mechanism of action. In: Saunders Handbook of Veterinary Drugs (Fourth Edition), 2016.

⁶Liang, L. Qiu, L. Vitamin E succinate with multiple functions: A versatile agent in nanomedicine-based cancer therapy and its delivery strategies. International Journal of Pharmaceutics, Volume 600, 1 May 2021, 120457.