 Equine
Protozoal Myeloencephalitis (EPM) is a master of disguise. This serious disease
can be difficult to diagnose because its symptoms often mimic other health problems
in the horse and signs can range from mild to severe. As many
as 50 percent of all horses in the United States may have been exposed to the
organism that causes EPM. The causative organ is a protozoal parasite named Sarcocystis
neurona. The disease is not transmitted from horse to horse. Rather, the
protozoa are spread by the definitive host, opossums, which acquires the organism
from infected birds. The infective stage of the organism, the sporocysts, are
passed in the opossum's feces. Tne horse comes into contact with the infective
sporacysts while grazing or eating contaminated feed or drinking water.
Once ingested,
the sporocysts migrate from the intestinal tract into the bloodstream and cross
the blood/brain barrier. There they begin to attack the horse's central nervous
system. The onset of the disease may be slow or sudden. If left undiagnosed and
untreated, EPM can cause devastating and lasting neurologic damage.
SYMPTOMS
The clinical
signs of EPM can be quite varied. Clinical signs are almost always asymmetrical
(not the same on both sides of the horse). Actual symptoms may depend on the
severity and location of the lesions that develop in the brain, brain stem or
spinal cord.
Symptoms
may include:
- Ataxia (incoordination),
Spasticity (stiff, stilted movements), abnormal gait or lameness
- Incoordination and
weakness which worsens when going up or down slopes or when head is elevated
- Muscle atrophy, most
noticeable along the topline or in the large muscles of thehindquarters, but
can sometimes involve the muscles of the face or front limbs
- Paralysis of muscles
of the eyes, face or mouth, evident by drooping eyes, ears or lips
- Difficulty swallowing
- Seizures or collapse
- Abnormal sweating
- Loss of sensation along
the face, neck or body
- Head tilt with poor
balance; horse may assume a splay-footed stance or lean against stall walls for
support
- Fatigue or narcolepsy
- horse may seem to suddenly fall asleep, or lie down for extended periods
Three
things seem to influence progression of the disease:
- 1. The extent of the
infection (i.e. the number of organisms ingested)
- How long the horse
harbors the parasite prior to treatment
- The point(s) in the
brain or spinal cord where the organism localizes and damage occurs
HORSES
AT RISK
 EPM
is considered the number one cause of neurologic problems in horses today. Almost
every part of the country has reported cases of EPM. However, the incidence of
disease is much lower in the western United States especially in regions with
small opossum populations. However, due to the transport of horses and feedstuffs
from one Part of the country to another, almost all horses are at risk.
Not all
horses who are exposed to the protozoan Sarcocystis neurona will develop
the disease and show clinical signs of EPM. Some horses seem to mount an effective
immune response and are able to combat the disease before it gains a foothold.
Other horses, especially those under stress, can succumb rapidly to the debilitating
effects of EPM. Still others may harbor the organisms for months or years and
then slowly or suddenly develop symptoms.
DIAGNOSIS
Your veterinarian
will first conduct a thorough physical examination to assess your horse's general
health and identify any suspicious symptoms. One notable clue is the disease
often tends to affect one side or part of the horse more than another.
If your
equine practitioner suspects EPM, he or she will order blood and cerebrospinal
fluid (CSF) analysis. A spinal tap, in which a long needle is inserted through
the back and into the spinal canal, will be necessary. The blood test alone,
while useful, is inconclusive as it may indicate exposure to the organism but
not whether the disease has attacked the central nervous system. A positive blood
test only means the horse has been exposed to the parasite, not that it has or
will develop clinical disease. Currently two laboratories are analyzing blood
and spinal fluid for EPM. Prompt, accurate diagnosis is essential and treatment
should begin immediately.
TREATMENT
Tne sooner
treatment begins, the better the horse's chances are for recovery. Sixty to 70
percent of EPM cases aggressively treated show significant or complete reversal
of symptoms. Many horses are able to return to normal activity.
Here are
some things you should know about treating EPM:
- At present, there are
no labeled anti-protozoal drugs approved by the FDA to treat EPM, consult your
veterinarian.
- Anti-inflammatory
drugs may be prescribed to alleviate symptoms and prevent reactions to parasite
die-off during treatment.
- Supplementation with
vitamin E, an antioxidant, is often recommended to aid healing of nervous tissue.
- Average duration of
treatments is 3-6 months, but can sometimes be longer.
- Current Practice is
to extend treatment 30-60 days beyond the elimination of symptoms or until a
negative CSF test is obtained.
- Long-term treatments
can be costly.
- Although complications
are rare, treatments may affect stallion fertility and may pose certain health
risks to unborn foals.
- While success rates
are high, not all horses respond positively to therapy. Approximately10-20% of
horses may experience a relapse.
- While a horse is being
treated, taking intermittent blood samples may be recommended to monitor potential
side effects such as anemia, low platelet count and low white blood cell count.
- Since some drugs used
to treat EPM are antifolate drugs, supplementation with folic acid (a B vitamin)
is recommended.
- Horses undergoing treatment
should be closely observed for signs of improvement or decline, especially negative
side effects to the drugs, such as acute diarrhea.
- Be sure to report any
changes in the horse's condition to your veterinarian.
METHODS
OF PREVENTION
Unfortunately,
there is little horse owners can do to adequately protect their horses from infection
with EPM. There are currently no vaccines to immunize animals against protozoal
diseases. At best, good horse-keeping practices will discourage unwanted visitors
such as opossums, other rodents and birds from contaminating hay, grain and bedding.
Here are
a few suggestions:
- Keep feed rooms and
containers closed and sealed.
- Use feeders which minimize
spillage and are difficult for wild animals to access.
- Clean up any dropped
grain immediately to discourage birds and other scavengers.
- Feed heat-treated cereal
grains and extruded feeds since these processes seem to kill the infective sporocysts.
- Keep water tanks clean
and filled with clean fresh water.
- Maximize your horse's
health and fitness through proper nutrition, regular exercise, and routine deworming
and vaccinations.
- Schedule regular appointments
with your equine veterinarian.
ONGOING
RESEARCH
EPM was
initially identiiied in 1964. In recent years, awareness among veterinarians
and horse owners has grown considerably. Research at the University of Kentucky,
the University of Florida, Ohio State University, the University of California
at Davis, and Michigan State University, as well as other institutions, is leading
to advancements in EPM diagnosis and treatment. For more information regarding
EPM, contact your veterinarian or the American Association of Equine Practitioners,
4070 Iron Works Pike, Lexington, KY 40511, (606) 233-0147.
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