E212
Equine Protozoal Myeloencephalitis (EPM)

More Horse Info

Introduction: EPM or equine protozoal myeloencephalitis is a disease that can affect horses of all ages; however, it is found most commonly in young thoroughbred, standardbred, and quarter horses. Horses that are stressed for any reason have an increased risk for developing the disease.

Causative Agent: EPM is caused by a protozoa parasite (Sarcocystis neurona). The parasite causes death (necrosis) of the brain stem and spinal cord.

Clinical Signs: Because EPM causes damage to the central nervous system (CNS), the majority of clinical signs are related to balance and coordination problems. These horses stumble, fall, and have gait abnormalities because they lack control of their limbs. Over time these horses can lose muscle conditioning and weight. Depending on the location of the damage in the CNS, some infections result in head tilt, facial nerve paralysis, seizures, blindness, and problems with the tongue and mouth. Some of these horses are easily moved from side to side by pulling on the tail. This disease can come on suddenly or progress slowly over time. If left untreated, most horses will become completely recumbent (unable to rise).

Disease Transmission: Horses are thought to get EPM by eating feed contaminated with fecal material from wildlife and carnivores. Some studies indicate that there is an increased chance for disease in areas where opossums have access to horses. Once the parasite is ingested, it makes its way to the CNS and brain.

Diagnosis: Diagnosing EPM can be pretty challenging. This is because a spinal tap to collect cerebral spinal fluid (CSF) is usually performed and the spinal fluid is then evaluated. In most cases there are elevated white blood cell, protein, and creatine phosphokinase (CPK) levels in the CSF fluid. In some rare cases the Sarcocystis neurona parasite can be identified directly. Most animals are diagnosed with EPM if they show clinical signs typical of EPM and if antibodies to Sarcocystis neurona are identified in the CSF sample.

Treatment: Some horses respond with extended antibiotic treatments using trimethoprimsulfa and pyrimethamine over a period of months. This treatment seems to improve 60-70% of affected horses. A new experimental treatment using triazine derivatives is now under investigation and has promising results.

Prevention: Because the exact method of how this disease is spread is not known, preventing this disease is difficult. At this time the best method for prevention is accomplished by keeping wildlife and carnivore animals from defecating on pastures or feed consumed by horses. Recently, Fort Dodge has developed a conditionally licensed vaccine to prevent EPM. Studies indicate that this vaccine is very safe and can be given to horses of all ages.