Equine protozoa myelitis (which, fortunately, is shortened to
EPM), is a common neurological disease. Although its symptoms can
appear similar to wobbler's syndrome, unlike wobbler's it can be
detected in more than one area of the spine.
EPM has been recognized in many breeds and ages of horses for
more than 20 years. It was called spinal segmental myelitis until
clusters of protozoa (single myelitis until clusters of protozoa
(single celled organisms were found around the affected nerves.
In the late 1980's the organism was identified as Sarcocystis
neurona, and an antibody test was developed.
Sarocystis neurona was originally thought to be concentrated in
Standardbreds, but is now known to occur in all horses in the
Western Hemisphere. Although the life cycle is not fully known,
recently the opossum has been determined to be a host within the
cycle, with birds acting as intermediaries for the parasite. The
incubation period for the disease is unknown.
EPM affects different neurons throughout the neurological system
and can result in dragging or spastic gaits. One side of the body
may be affected, but not the other. The organism can also cause
muscle atrophy in the jaw and forehead. If it affects the cranial
nerves, the horse may have problems eating or drinking, have
facial twisting, or undergo changes in the position of the eyes
and ears. Severe cranial infection can even cause bizarre changes
in behavior or seizures.
Diagnosis of EPM is based upon finding antibodies or, more
recently, a DNA detection test of either blood or cerebrospinal
fluid. Blood antibody titers, however, should not be considered
evidence of the clinical disease. Although spinal fluid samples
are more difficult to obtain, they are more reliable. The DNA
test is used to identify the presence of the organism in the
The good news for horse owners is that EPM is treatable in the
long-term with sulfa drugs and an antimalaria medication. Since
these drugs can cause anemia, folic acid is added to the diet.
Vitamin E has also been found to aid in nerve healing and is
added to the daily regimen. About 70 percent of horses respond to
treatment, although the level of clinical response may not result
in full recovery. Horses have been known to compete at the top
levels after treatment.
Equine protozoal myelitis should be considered a common endemic,
not epidemic, disease. Horse owners should treat the disease
aggressively, knowing that this is one of the neurological
diseases that justifies optimism. Your horse can get better if