What Every Veterinarian Needs to Know About EPM in Horses

Equine Protozoal Myeloencephalitis (EPM) is a severe neurological equine disease most frequently caused by the protozoan parasite Sarcosystis neurona. EPM in horses is a life-destroying disease if undiagnosed and untreated. 

Veterinarians must be well aware of signs, testing, and treatment procedures to manage this disease efficiently. In this blog, we will learn what EPM is in horses, horse EPM signs, treatment of EPM, and a lot more.

What is EPM in Horses?

EPM, or Equine Protozoal Myeloencephalitis, is an infectious disease that infects the central nervous system (CNS) of the horse. It happens when the horse becomes infected with the parasite Sarcosystis neurona, which can cause brain and spinal cord inflammation. The parasite is best spread through opossum feces, and although it infects many different species, it is most undesirable in horses.

Horses are dead-end hosts for the parasite, i.e., they do not pass the parasite to other animals. The presence of opossums near the horse environment raises the infection risk.

The Mechanism Behind EPM

When horses ingest food, water, or bedding with S. neurona oocysts from the opossum feces, the parasite enters the body of the horse and moves to the CNS. Upon arrival, it leads to spinal cord and brain inflammation, causing neurological symptoms like unsteady gait, weakness, and wasting of muscles.

Identification of the cause and mode of transmission of EPM is important to prevent it, particularly in areas infested with opossums.

Signs of EPM in Horses

It is critical to identify the signs of EPM in horses early enough for the treatment. Being a neurological disorder, EPM has very broad clinical signs that depend on the areas of the brain and spinal cord involved.

Common Symptoms of EPM

• Unilateral weakness or asymmetry: Horses may experience lameness in a single leg or weakness on one side of the body.
• Incoordination (ataxia): This is one of the most common presentations of EPM. Horses will be ataxic at a walk and exhibit stumbling, swaying, or weaving.
• Facial muscle paralysis: Horses with facial muscle paralysis may have trouble chewing or spilling food, especially if the disease involves the face-controlling muscles.
• Abnormal posture: The horses may be standing in abnormal positions, including leaning to one side or taking a wide stance for support.
• Muscle twitching or tremors: The impact of the parasite on the nervous system can cause spontaneous movement of the muscles.
• Head tilt: In others, the horse will tilt the head to a side as a result of nerve damage.

Depending on the severity of the disease, the symptoms can be mild or severe. Therefore, veterinarians must carry out thorough investigations when EPM is suspected.

What are the Early/First Signs of EPM in Horses?

The early symptoms of EPM are not apparent, and the owners might not even know that there is anything wrong. The first symptoms could be a little imbalance, loss of coordination, or inability to perform something easy previously. The first symptoms might be confused with other issues, so a veterinarian needs to diagnose accurately.

How to Test for EPM in Horses

If a veterinarian suspects EPM, there are many diagnostic tests to confirm that the parasite is present.

Common Diagnostic Tests

Serum and cerebrospinal fluid (CSF) testing: This is the most reliable test for the diagnosis of EPM. The presence of antibodies against S. neurona in the CSF will diagnose the infection. A positive serum test alone does not confirm EPM because it may be a sign of exposure and not active infection.

Western Blot Assay

Both CSF and blood samples can be tested with this assay to detect antibodies. Positive results confirm the diagnosis, but a negative test does not rule out the disease.

PCR testing

A polymerase chain reaction (PCR) test can diagnose parasite DNA in cerebrospinal fluid with the absolute certainty of infection.

Is EPM Contagious in Horses?

Another question that many veterinarians and horse owners have is if and how contagious EPM is. No, EPM is not contagious among horses. The disease is caused by a protozoan parasite that needs an intermediate host, like the opossum, to complete its life cycle.

Horses are dead-end hosts in that they do not pass the parasite to other horses. But horses in high-density opossum territory may be at greater risk.

EPM in Horses Treatment: What are the Choices?

EPM in horses is a severe disease, but curable with proper treatment and preventive measurements. The ultimate aim of treatment is to eliminate the parasite from the horse's CNS and alleviate inflammation.

Treatment Options Shared by Most Horses

Antiprotozoal Therapy

Sulfadiazine and pyrimethamine are the most prevalent drugs used to cure EPM. The medication stops the reproduction of the S. neurona parasite. Therapy takes around 60-90 days.

Anti-Inflammatory Medication

Corticosteroids or non-steroidal anti-inflammatory medication (NSAIDs) can be administered to suppress CNS (Central Nervous System) inflammation and swelling, which relieves symptoms and allows the body to heal.

Supportive Care

In addition to therapy, supportive care such as physical therapy, nutrition support, and good management practices play a very important part in recovery. Horses can recover with a limited exercise program to regain muscle strength and coordination.

Can EPM in Horses Be Cured?

The short answer is yes; EPM can be effectively treated with timely intervention. But treatment requires commitment and patience. Horses that are treated early have a good prognosis to fully recover, but horses that are seen with more severe neurological symptoms take longer to recover. 

The effectiveness of the treatment also depends on the horse's condition, age, and timeliness of treatment. Though most horses recover from the treatment, long-term effects in some horses develop, e.g., mild neurological deficits. Early diagnosis and rigorous treatment will minimize such long-term effects.

Long-Term Effects of EPM in Horses

A few horses will have long-term effects despite successful treatment. The long-term effects may broadly vary depending on how severe the disease was and what areas of the CNS were affected. Common long-term effects are:

• Residual ataxia or weakness: The horse may remain with minimal signs of weakness or incoordination in one or more legs.
• Muscle atrophy: If it affects the muscle, there is going to be irreversible wasting of the muscle, and this requires ongoing management.
• Chronic pain: Damage to the spinal cord or other neurological tissue leads to chronic pain, and thus, continued measures to manage pain are necessary.

Regardless of these issues, the majority of horses recover and resume their routine, such as riding and competition.

EPM in Horses vs. Other Neurologic Diseases

Comparison of EPM Treatments: What Works Best?

Veterinarians often have trouble determining the ideal treatment for a horse with EPM. Here, we compare the two dominant forms of treatment regimens:

Antiprotozoal Medications

Antiprotozoal medications like sulfadiazine and pyrimethamine target the parasite directly, with the goal of eliminating it from the horse's system. This is crucial in halting the progression of the disease.

Supportive Therapy

Supportive therapies, including NSAIDs and physical therapy, are utilized to manage the symptoms and improve recovery but does not have an action against the parasite. These are imperative in making the horse comfortable as well as enhancing the quality of life in recovery.

Though both are essential, priority should first be given to antiprotozoal drugs, with supportive care as a second line.

Conclusion

EPM in equines is a complex and sometimes crippling disease but, with the right diagnosis and treatment, most horses can overcome the condition fully. As an equine vet, it pays to know how to recognize signs of EPM in horses in their early stages and the most appropriate diagnostic testing to determine the presence of the parasite. 

Early application of antiprotozoal medication, followed by supportive management, will maximize success. For further information about equine health, such as symptoms of ulcers in horses, check out our veterinary blog for the most recent information. 

If you're searching for animal health products or require help with veterinary services, DVM Central offers an extensive range of products for horse care.

FAQs

What are the initial signs of EPM in horses?

The initial presentation of EPM in horses is usually mild incoordination (ataxia), asymmetrical muscle wasting, and mild lameness. These can be subtle and easily mistaken for other neurological or orthopedic conditions. Neurological examination must be performed by equine veterinarians, and EPM should be considered as a differential diagnosis, particularly in horses that have been exposed to opossum-contaminated environments.

How to test for EPM in horses?

Testing for EPM in horses involves a combination of clinical evaluation and laboratory diagnostics. The gold standard includes CSF analysis via western blot or PCR testing for S. neurona antibodies. Paired serum: CSF antibody ratio testing helps differentiate actual infection from mere exposure. Early testing allows for the timely initiation of EPM in horses' treatment plans.

Is EPM contagious in horses?

No, EPM is not contagious. Horses do not transmit EPM to one another. The causative parasites (Sarcocystis neurona and sometimes Neospora hughesi) are spread through fecal contamination by opossums, not from horse-to-horse contact. Preventive veterinary services often include biosecurity education on minimizing opossum exposure around barns and feed storage areas.