EPM
EPM Equine Protozoal Myelitis is an infectious neurologic disease of horses in North America. EPM can affect any horse and cause irreversible damage to the brain and spinal cord if left unchecked. Today we know EPM can be caused by Sarcocystis neurona and Neospora hughesi (possum parasites). 75% of healthy horses in the US are carrying antibodies to EPM but only 1% succumb to clinical disease.
S. neurona makes up 85-95% of the cases. The number of horses with exposure to this parasite as evident by the antibodies in their blood serum sample is 84% to S. neurona and do not have neurologic clinical signs. Horses exposed to the organism can mount an immune response and develop antibodies, but some cannot. Those horses that do succumb to clinical illness seem to be either immune compromised or unable to prevent the protozoal organisms from entering the central nervous system (spinal cord).
More than 1/3 of healthy horses in the US (41% in the south) are positive on serum blood test for Neospora hughesi. Once it is in the horse it stays forever and can be transmitted from dam to offspring. During times of immunosuppression, such as pregnancy, the organism is reactivated and, in some cases, will cross the uterus- placenta and infect the fetus. It is not uncommon for a horse with neuronal neosporosis to have comorbidity with metabolic, endocrine, and other chronic infectious diseases. It is thought that these comorbidities suppress the immune system enough to allow for an effective reemergence of the dormant N. hughesi with subsequent invasion of the neuro system (spinal cord). Toxaplasma gondi can play a role in some EPM cases. More research is being done on it.
EPM is caused by the horse ingesting feed or water contaminated with possum feces. Feeding on the ground, or in feeders and eating the spilled feed on the ground, can result in exposure. At night, if a possum comes by to eat the feed, it can pass feces and contaminate it. If a horse then eats that feed, it can ingest the possum parasite from the possum feces.
Risk factors for EPM
- Age. Young performance horses and old horses.
- Sickness. Horses with a suppressed immune system
- Career. Vigorous exercise, training, travel, and competition.
- Environment. Wooded areas, previous history of EPM on premises, summer, fall, feeding on the ground, drinking from a pond contaminated with possum feces.
- Pregnancy.
Signs of EPM
- Asymmetrical weakness
- Ataxia (unbalanced in the hind end, wobbling).
- Incoordination
- Localized muscle atrophy.
Diagnosis
Diagnosis is by neurologic signs, blood test, spinal fluid test for antibodies, and response to treatment. The earlier the disease is caught and treatment begins, the better the outcome.
Treatment
Treatment is with Diclazuril (Protozil oral pellets by Merck), Marquis paste, or Rebalance liquid. Treatment with compounded pharmacy drugs (Totrazuril) have not been tested by the FDA for effectiveness and safety. Anti-inflammatory drugs (Banamine, Bute, DMSO) are essential to help reduce the inflammation of the neurologic system (spinal cord). Antioxidants, such as vitamin E, are often recommended for horses with neurological and neuromuscular conditions.
Prevention
EPM can be prevented by not feeding horses on the ground. Clean up spills from feeders to limit the horse from digesting contaminated feed. Provide fresh drinking water in a trough. Do not use a pond as the primary water source. Minimize stress, travel. Diclazuril (Protazil by Merck) given at a low dose or once a week provides blood levels that inhibit S. neurona.
In a study, young horses 1 month to 1 year were give a low dose of diclazuril daily for a year. The horses in the control group 88% had positive blood tests for EPM while only 6% of the diclazuril treated horses had positive blood tests. We know that a horse must test seropositive on the blood test to develop EPM so in theory we have reduced the risk of treated horses developing EPM. Since the horse is a dead end host (the horse does not pass the parasite in their feces), there is minimal risk of drug resistance developing.
The cost for feeding a low dose ½ dose daily of Protozil is $350/month 1 bucket last 2 months The cost for feeding Protazil once a week is $ 30/week or $120/month The bucket costs $700. There are 24 doses/bucket so that is treatment for 6 months. 1
AAEP
Dr Hayes will be in San Antonio attending the AAEP American Association of Equine Practitioners meeting Friday November 18 thru Tuesday November 22. There will not be a veterinarian available to see patients during this time. Dr Hayes will be returning to work Wednesday November 23. Our office will remain open during normal business hours.
We will be closed Thursday November 24 for Thanksgiving, and will resume normal business hours on Friday November 25.
Castration signs November 25-30
Congratulations to our secretary Betty Ann and her home bred Appaloosa Stallion White Collar Crime! “Enron” won the foundation bred halter class at the Appaloosa World Show and is now a World Champion and Bronze Medallion winner.
Reference: 1. Nicolas Pusterla DVM DACVIM
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