EPM Symptoms Summary

EPM can cause lesions anywhere in the brain or central nervous system (CNS). That means symptoms or deficits can show up anywhere in the head or body. The lesions can cause temporary inflammation and permanent nerve damage. Symptoms that are a result of inflammation may get worse during treatment, and then disappear faster after the protozoa are killed. Symptoms that are a result of permanent nerve damage may never go away. The horse may learn to compensate for the loss of feeling, or may generate new nerve pathways around the damaged cells.

Not all researchers agree on the incubation period; however, clinical trials and horse shipments to continents without EPM, have suggested it takes from weeks to two years for symptoms to appear after infection by S. neurona. A very rapid onset is occasionally possible, with severe symptoms occurring quickly. Rapid onset is thought to occur with ingesting large amounts of protozoa. The longer the disease is left untreated, the more numerous symptoms become, and the worse they will be. The earlier these symptoms are identified, a diagnosis obtained, and treatment begun, the better the chance of a substantial recovery.

The long list of possible symptoms can make EPM very hard to diagnose. You should not suspect EPM from a single symptom like lameness, rather from a pattern of symptoms that are not explained by other diagnoses. Many times the owner will recall possible symptoms that occurred months before a diagnosis, but did not recognize them as a pattern.

Detecting Subtle EPM Symptoms

The best way to detect subtle symptoms early in the disease is to know your horse well. Learn the way that the healthy horse eats, walks out to the pasture, behaves, poops, and moves under saddle and free. Changes to the norm should be noted and watched. If you board your horse and only ride occasionally, the barn staff may know your horse’s off-time behavior better than you do. If they mention that something doesn’t seem right, pay attention: the earliest symptoms may not be the ones felt under saddle. There are many possible symptoms; you are looking for changes to the norm. A fever accompanying the symptoms generally means it is not EPM.

Common EPM Symptoms of the Body

A very common symptom reported for EPM is uncoordinated movement of the rear feet, worse on one side (asymmetrical ataxia). This symptom is often worse moving uphill or downhill, and while stopping or raising the head.
Lameness issues that come and go, often switching sides
Changes to any gait, lethargy
Hind end weakness - worse on ground that slopes left to right or front to back
Problems balancing when a hoof is lifted
Circling, slipping, or falling while walking
Muscle atrophy, often over the rump or shoulders
Leaning on a stall wall for balance
Standing with a hoof cocked out or in, not standing square
Dragging a hoof, especially while turning
A sore back, changes in the fit of the usual saddle
Unusual sweating patterns or times
Carrying the tail to one side, or away from the body
Lack of sensation or heightened sensitivity in skin or hooves
Falling in the herd dominance order

Common EPM Symptoms of the Head

A drooping lip or repeated facial twitch
Change in vision
Trouble eating or swallowing
Head tilt
Drooping ear
Changes in behavior, including throwing the rider

Less Common EPM Symptoms

Geldings that drop other than when urinating
Extreme lethargy
Changes to manure

References:

www.TheHorse.com search articles for EPM Symptoms

http://www.dclahdvm.com/articles/epm.htm

http://www.aaep.org/health_articles_view.php?id=278