Horse Owner Information

A horse owner often knows when their horse is under the weather, before the signs of EPM are recognizable.  I wrote a paper describing the Early Signs of Equine Protozoal Myeloencephalitis that can help you recognize early disease. The paper is based on experimental infections, we knew the day they were infected and could keep an eye out for those subtle signs as they appeared. Click this link to read about our observations.  Ellison 2003Early Signs

Sometimes signs aren't so vague, the horse can be severely wobbly (ataxic) or even so bad they are unable to get up. It can happen overnight!  And at other times, the horse has been suffering with EPM so long that a dull, distracted demeanor is accepted as "normal".


This is Lily, she was one of our first long-distance encounters with an acute case of EPM.  We were designing a treatment for EPM that would address inflammation, part of the EPM syndrome.  She was normal in the morning, that afternoon she was unable to walk, severely wobbly, when her owner came home from work.

Lily had acute inflammation associated with S. neurona infection. Equine protozoal myeloencephalitis is a syndrome.  The components of the syndrome are infection and inflammation.  An active infection means that replicating protozoan parasites (merozoites) are in the horse. Chronic infections indicate parasites are dormant and then an unknown trigger activates them.  Inflammation accompanies acute or chronic infections, or inflammation can linger long after parasites are eliminated. We were quickly able to relate our laboratory studies in horses to Lily's condition. We hadn't yet developed some of our more advanced tests that may have helped with treating Lily.

Have a horse with EPM?  Take advantage of our Client Communication and call us with any questions.


A therapy plan should include multiple exams, multiple tests, and quick evaluations to the response to treatment. A plan should be based on objective data that was derived from experiments.  Our database combines thousands of subjective and objective measurements from horses across the country. And our work is based on an experimental model that induces disease and extensive field trials that give us feedback from veterinarians.

The antibody found in the horse serum is our target.  That antibody is detected by a “detector reagent” that is tagged with an enzyme.  How we set up our tests (which protozoan protein, inflammatory markers, markers for autoimmune disease) makes the disease distinction between tests.

We use surface proteins from the S. neurona organism to test the sample taken from the horse. There are some proteins that are “common” to all coccidia and some that are specific to one of three individual serotypes of S. neurona.  Non-specific tests (IFAT, SAG 2, 4/3) measure the common proteins found on all protozoa and overestimate the disease, that result is called a false-positive result.  If you are measuring S. neurona you don't want to detect S. fayeri. These common-antigen tests won't tell you the serotype of S. neurona like our SAG 1, 5, 6 tests do.  The serotype is the level a horse can detect, genetic differences are left to the molecular biologists.

The S. fayeri test measures the amount of anti-toxin found in the serum.  Antitoxin is a reaction to muscle cyst proteins found in S. fayeri infected horses. Laboratories that run "EPM" testing dilute the serum, or suggest spinal fluid testing, to exclude S. fayeri antibodies because they would give a "false positive" S. neurona result.  The exclusion is based on a long held belief that S. fayeri doesn't cause neuromuscular dysfunction, the big words for a wobbly horse. Researchers at CA-Davis looked for cysts in muscles of sick horses and related it to neuromuscular disease; we published a paper that related disease to the toxin produced by the cysts. Our work provided statistical significance to the finding of S. fayeri and clinical signs.

Sarcocyst in muscle tissue

Our observations proved to us that a common factor in disease caused by S. neurona and S. fayeri (by the way, the disease caused by either of these organisms is called sarcocystosis) was inflammation. Inflammation is measured by our CRP test.  Amazingly, horses that responded to anti-protozoal treatment that had continually elevated CRP values would eventually relapse.

One of our field studies is gathering data from chronically relapsing EPM-horses. The early results of the study are under review for publication.  If you have a horse with chronic, relapsing EPM it isn't too late to enroll into the study.

The Cliffs Notes for the study are:

1-three conditions are associated with sarcocystosis, EPM, S. fayeri toxicosis, and autoimmune polyneuritis;

2-the EPM group describes only 8% of over 80 horses with chronic, relapsing/remitting disease;

3-autoimmune polyneuritis, horses with antibodies against myelin covering of nerves, was seen in 43% of the horses;

4-S. fayeri anti-toxin was detected by our tests in 49% of the chronically ill horses;

5-the three conditions require different treatment.

We have a plan to keep these horses healthy, the most crucial aspect of disease management is using your veterinarian to help with the management of the signs using the most up to date treatment and treatment protocols.  Testing the serum for CRP levels can let the veterinarian know if the inflammation is controlled.  The good news is that we are following 47 cases of autoimmune polyneuritis and they are doing well. Some have been taken off the medication because their blood tests show no more inflammation.  We will continue to monitor them, gathering data, and publish our long-term findings.

The first step to returning health to a horse that has been treated multiple times with EPM drugs is to test them. Submit the serum sample to us and we will get your results back to your veterinarian quickly. ELISA Submission Form  If you don't know which tests to select just give us a call at 352-591-3221.  We will consult with you and your veterinarian and share our knowledge with the EPM community.