Equine Protozoal Myeloencephalitis (EPM) Tests

Industry-leading EPM testing from IDEXX

  • EPM by Western Blot (Serum)
  • EPM by Western Blot (CSF)

Twelve years of collaboration with prominent researchers, along with countless conversations and consultations with veterinarians in the field, places IDEXX in a unique position. Since 1995, we have tested thousands of EPM specimens and accumulated a wealth of experience, expertise and a vast store of information about EPM.

EPM is a common neurological disease seen throughout the United States, and is strongly suspected in horses that present with clinical signs of neurological disease and a positive Sarcocystis neurona antibody response in the cerebrospinal fluid (CSF). However, exposure to S. neurona does not necessarily mean that the clinical signs of disease will occur. It’s impossible to predict which horses may display neurological signs of the disease based simply on the presence of serum antibodies, which only indicates that the horse was exposed to S. neurona.


Additional EPM testing options available:

  • CSF Index (Serum and CSF)
  • Cell Count and Differential (CSF)
  • EPM Profile I by Western Blot (Serum and CSF)
  • EPM Profile II by WB and PCR (CSF)
  • EPM Profile III by WB (serum and CSF) and PCR (CSF)

Understanding Equine Protozoal Myeloencephalitis (EPM)—Risk factors and signs

Know the risk factors for EPM1

  • Exposure to any site where EPM has been detected previously
  • Grazing pastures and/or feed accessible to other wildlife (especially opossums)
  • Excessive heat that may weaken the immune system
  • Age—especially horses one to five years of age
  • Stressful events, including trailering, breeding, showing, selling, training, foaling and nursing

Know the signs of EPM

Presenting clinical signs can be quite variable because they’re related to where lesions occur in the central nervous system. The most common clinical signs for EPM at presentation include asymmetric ataxia and focal muscle atrophy in the gluteal, or rump, area (most frequently). Other commonly observed clinical signs include:

  • Asymmetrical ataxia
  • Lack of coordination that worsens when the head is elevated
  • Stiff, stilted movements
  • Muscle deterioration (hindquarters, muscles of the face or front limbs)
  • Difficulty swallowing or loss of appetite
  • Facial muscular paralysis or loss of sensation
  • Stumbling
  • Seizure
  • Change in personality
  • Fatigue or narcolepsy
  • Head tilt with poor balance
  • Abnormal sweat patterns (focal sweating)
  • Head shaking


IDEXX testing recommendations:

  • Our Western Blot (WB) Test detects S. neurona-specific IgG.
  • The presence of S. neurona-specific IgG in serum indicates exposure to this parasite, but not necessarily disease.
  • In the presence of neurologic signs, the presence of S. neurona-specific IgG in cerebral spinal fluid (CSF) indicates active disease.
  • The EPM Profile 1 is recommended on a horse exhibiting neurologic signs.

Sample requirements

Refer to our Sample Submission Instructions to view the different sample collection guidelines for each type of test.

Turnaround times

The IDEXX EPM testing is performed daily, Monday–Friday.
Western blot results are available within 24 hours if the sample is received by noon.


Reference Library

Educational Partner

IDEXX is an Educational Partner of the American Association of Equine Practitioners

1.  Saville W, Reed S, Morley P, Granstrom D, Kohn C, Hinchcliff K, Wittum T. Analysis of risk factors for the development of equine protozoal myeloencephalitis in horses. JAVMA. 2000;217:174–180.