Equine Protozoal Myeloencephalitis (EPM) is an extremely serious disease of horses which can be very difficult to diagnose because its signs often mimic other disorders and its signs can range from mild to severe. The causative organism in EPM is the protozoal parasite Sarcocystis neurona. The disease is transmitted to the horse by the definitive host, the opossum, rather than acquiring it from other horses. Horses come into contact with the infective S. neurona sporocysts while grazing or eating feed or drinking water contaminated with opossum feces. EPM only occurs in the Americas (North, South and Central America) where opossums are found. Some cases of EPM have also been attributed to the protozoan N. hughesi.

EPM: The Disease Process

Once the sporocysts are ingested, they migrate from the intestinal tract into the bloodstream and cross the blood/brain barrier.¹ There, they attack the horse's central nervous system (CNS). The onset of EPM can be slow or sudden; if left untreated, it often causes severe, lasting neurological damage.

EPM causes clinical disease in approximately 1% of horses that have been exposed to the S. neurona or N. hughesi protozoa. Some horses are apparently able to to mount an effective immune response and clear the protozoa before it can cause clinical disease. Other horses may succumb rapidly to the disease. Still other horses harbor the organisms for months or years and then develop symptoms. Nearly every region in the United States has reported cases of EPM, with lower incidence in regions with small opossum populations.² Due to the transport of horses and feedstuffs from around the country, nearly all horses are at risk for EPM.

Measures taken in preventing EPM include decreasing stressors and reducing exposure to opossum feces. Precautions like feeding horses in feeders (rather than on the ground), maintaining separate fresh water sources, preventing wildlife access to areas where horses are housed, properly disposing of animal carcasses, keeping feed rooms and containers closed and cleaning up dropped grain can help reduce protozoal infections.¹

Signs of EPM in the Horse

Clinical signs of EPM are predicated upon the area of the central nervous system that contains the parasite and the type and degree of damage that has been caused. The onset of EPM can be gradual or sudden. In the case of spinal cord involvement, a horse may display gait abnormalities, poor coordination, ataxia, spasticity in the limbs and muscle atrophy.

In the case of brainstem involvement, the horse may display lethargy, behavioral changes, and cranial nerve paralysis. The clinical signs may be asymmetrical (different on either side of the horse). The horse may stand with its feet splayed, or lean against supporting structures. Occasionally, clinical signs may stabilize only to recur days or weeks later.

The Association of Racing Commissioners International Uniform Classification Guidelines for Foreign Substances has designated levamisole a CLASS 2 DRUG.

In horses, sulfadiazine is used in the treatment of acute strangles, respiratory infections, equine protozoal myeloencephalitis, acute urogenital infections, wound infections, abscesses, and uterine infections. It is also used as a treatment or prevention of post parturient infections, including vaginitis and metritis.⁴

Where to buy Diclazuril + Levamisole + Pyrimethamine + Sulfadiazine + Vitamin E

Diclazuril + Levamisole + Pyrimethamine + Sulfadiazine + Vitamin E is available in the U.S. 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 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.

²Dubey, 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.

⁴equimed.com.