RICHMOND COUNTY — A few weeks ago, we encountered a horse with symptoms that the owner associated with dental issues. The horse was dropping feed due to a slack tongue and struggled to chew feed properly.
I advised that the owner call a veterinarian to evaluate the horse and possibly perform a procedure to smooth its teeth, called floating. According to the owner, the veterinarian came to evaluate the horse and after seeing the symptoms, decided to test the horse for Equine Protozoal Myeloencephalitis (EPM). The test came back positive.
EPM is a serious disease can be difficult to diagnose because its signs often mimic other health problems in the horse, and signs can range from mild to severe. According to University of Minnesota, more than 50 percent of all horses in the United States may have been exposed to the organism that causes EPM but only 1 percent actually develop the EPM disease.
The organism that causes EPM is a parasite called Sarcocystis neurona. The disease is not transmitted from horse to horse (one horse cannot spread it to another). Instead, the protozoa are spread by a host we commonly see at night, the opossum, which picks up the organism from raccoons, and skunks. It should be noted that only 20-30 percent of opossums are carriers of the parasite so not every opossum is infected.
The infective stage of the organism (the sporocyst) is spread through the opossum’s feces which then come into contact with the horse during grazing or by eating contaminated hay or drinking water. Once ingested, the sporocysts migrate from the intestinal tract into the bloodstream and attack the horse’s central nervous system. The onset of the disease may be slow or sudden. If left undiagnosed and untreated, EPM can even cause neurological damage.
What are the symptoms?
The signs of EPM can vary from horse to horse. Based on research and speaking with the vet, symptoms are usually asymmetrical (not the same on both sides of the horse). Actual signs may depend on the severity and location of the damage that develop in the brain.
Signs may include:
• Ataxia (incoordination), stiff movements, or lameness
• Muscle atrophy, most noticeable along the topline or in the large muscles of the hindquarters, but can sometimes involve the muscles of the face.
• Paralysis of the face or mouth such as drooping lips
• Difficulty swallowing
• Abnormal sweating
• Horses may lean against stall walls for support
Is my horse at risk?
EPM is considered the number-one cause of neurological 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. Not all horses exposed to the protozoan 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, however, especially those under stress, can succumb rapidly to the debilitating effects of EPM. Still others may be infected by the organism for months or even years before developing symptoms.
How do I know it’s actually EPM?
Having a good relationship with a veterinarian is important with any livestock or equine owner. Horses should receive annual or semi-annual vaccines for other diseases so this provides horse owners with a great opportunity to have routine visits from the vet. If you suspect that your horse is suffering from EPM, a veterinarian will need to evaluate the horse and they may order blood and cerebrospinal fluid (CSF) analysis.
Cerebrospinal fluid may be collected by way of a special needle inserted into the spinal canal either in a site on the lower back or at the poll. Potential risks are involved with the procedure and should be discussed with your veterinarian. A positive blood test only means the horse has been exposed to the parasite, not that it has or will develop clinical disease.
What are the treatments?
The sooner treatment begins the better the horse’s chances are for recovery. Sixty to seventy percent of EPM cases aggressively treated show significant or complete reversal of symptoms. Many horses are able to return to normal activity. Here are somethings you should know about treating EPM:
• At present, there are two 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 may be recommended to aid in repair of the nervous system.
• Average duration of treatment is one month with prescription medications, but depending upon which medication is used, it can sometimes be longer (up to 3–6months with combinations).
• Treatments can be expensive (over $300 dollars for medication alone).
• 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. Approximately 20% of horses may not completely recover.
• Horses undergoing treatment should be closely observed for signs of improvement or decline, especially negative side effects to the drugs, such as diarrhea or change in feed consumption.
• Be sure to report any changes in the horse’s condition to your veterinarian.
Developing a good relationship with your veterinarian is important to have access to proper care to keep your horses healthy. If you have any questions about livestock or equine management please contact the Richmond County Extension office, 910.997.8255.
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