Shedding Light on EPM: What Every Owner, Rider & Trainer Should Know
When we think of “neuro” disorders in horses, many jump-sport participants immediately think of cervical vertebral compressive myelopathy (CVCM) or equine degenerative myelopathy. But one of the most insidious, under-recognized neurological conditions in U.S. equids is Equine Protozoal Myeloencephalitis (EPM). At Steffee Showjumping, our mission goes beyond training — we believe that education and awareness are crucial to preventing and mitigating disorders like EPM, especially in the South, where risk factors tend to be higher.
What Is EPM?
EPM is a neurological disease caused by protozoal parasites — most often Sarcocystis neurona and less commonly Neospora hughesi — that invade the central nervous system (spinal cord and brain) of horses.
The definitive host for S. neurona is the opossum, which sheds infective sporocysts in its feces. Horses become accidental (dead-end) hosts when they ingest contaminated feed, water, or pasture.
Interestingly, serological surveys show that 22% to 65% of horses in parts of the U.S. test positive for antibodies to S. neurona, depending on geography. Yet, far fewer—less than 1% annually—develop clinical disease.
In plain terms: many horses are exposed, but only a fraction ever become clinically affected.
Why the South Is Particularly Concerned
Though EPM has been documented across most of the continental United States (all 48 contiguous states), conditions in the southern U.S.—warmer climate, more wildlife interface, wetter seasons—tend to favor higher parasite survival and more frequent exposure.
Moreover, public awareness remains limited. In a USDA/APHIS survey, nearly 60% of horse owners/operators nationwide had never heard of EPM at the time of the interview; in the South especially, knowledge was lower. This gap in awareness hampers early detection and intervention, which are critical for better outcomes.
Recognizing the Signs: What to Watch For
The clinical presentation of EPM varies greatly, depending on which part(s) of the central nervous system are affected. Some common red flags include:
- Asymmetrical gait abnormalities, stumbling, incoordination
- Weakness, especially in one side or limb
- Muscle atrophy (wasting), often focal
- Sudden lameness that doesn’t respond to standard lameness treatment
- Difficulty swallowing, head tilt, cranial nerve signs (in more severe cases)
- Changes in behavior, reluctance to move, dragging toes
Because these signs are not unique to EPM, diagnosis often involves ruling out other neurological or musculoskeletal causes. Diagnostic tools may include neurologic exams, cerebrospinal fluid (CSF) analysis, antibody testing (serum and CSF comparison), and advanced imaging where feasible.
Time is important. The earlier intervention begins, the better the chance to limit irreversible damage.
Treatment & Prognosis
There is no vaccine currently available to prevent EPM. Once diagnosed or strongly suspected, treatment typically includes:
- FDA-approved antiprotozoal drugs such as Marquis (ponazuril), ReBalance (sulfadiazine + pyrimethamine), or Protazil (diclazuril). These reduce parasite load but may not eliminate all organisms.
- Anti-inflammatory therapy (NSAIDs, corticosteroids) to reduce spinal cord inflammation and secondary damage.
- Supportive care: antioxidants (vitamin E), physical therapy, controlled exercise, and supportive stable management.
- Rehabilitation over weeks to months, tailored to the horse’s deficits and recovery rate.
Studies report that 57–62% of treated horses show improvement in clinical signs. However, complete recovery is not guaranteed, and relapse rates of 10% or more are documented.
It’s critical to manage expectations: while many horses respond well, the degree of neurological damage incurred prior to treatment often dictates the ceiling of recovery.
Prevention & Best Practices at Steffee Showjumping
At Steffee Showjumping, we incorporate preventive strategies into everyday stable management to reduce EPM risk:
- Feed & Hay Handling: Keep all feed and hay off the ground, in sealed bins or containers.
- Limit Opossum Access: Secure trash, compost, and remove decaying carcasses. Use fencing or barriers to discourage opossum intrusion.
- Water Hygiene: Ensure clean, flowing water sources; avoid stagnant water where contamination may accumulate.
- Pasture & Stall Management: Rotate pastures, mow brush, and limit areas where opossum feces might build up.
- Monitoring & Prompt Response: Encourage owners and riders to report subtle neurologic changes immediately.
- Education: Host clinics, share literature, and engage local vet partners on EPM awareness.
When clients board or train with us, part of our standard orientation includes discussing EPM risk, signs to watch for, and best practices for prevention.
Why Awareness Matters
EPM’s combination of wide exposure but relatively low clinical conversion makes it a tricky adversary. Many horses are seropositive without showing disease. But for those that do develop neurologic signs, delays in recognition can result in irreversible injury.
In regions like the Southern U.S., where environmental and wildlife factors elevate risk, awareness is not optional — it’s essential. By educating our community of riders, owners, trainers, and veterinary partners, Steffee Showjumping hopes to reduce the time to diagnosis and maximize successful outcomes for affected horses.
When to Act
If your horse shows even mild irregularities in gait, hind-end weakness, asymmetry, or other neurologic signals, please don’t wait. Contact your veterinarian immediately and mention possible EPM. Early veterinary evaluation can make all the difference.
At Steffee Showjumping, we’re committed to combining high performance with responsible stewardship of equine health. Together, we can shine more light on EPM, reduce its impact, and protect the athletic futures of more horses.
