EPM Update: New Treatment and Prevention

New EPM medication and proposed prevention regime

A medication similar to Marquis (the only approved medication to treat EPM), but in a top dress pellet form will be introduced in early December. Both Marquis and this new medication(generic name diclazuril), prevent the EPM protozoa from growing and replicating. Neither actually seem to kill the EPM organism. However, the body’s own immune system can kill the protozoa once it stops multiplying. Dr. Tom Divers, of Cornell Veterinary School, presented the information at a recent seminar. Dr. Divers explained that diclazuril more easily crosses the blood brain barrier than ponazuril, the active ingredient in Marquis. Both medications have a wide margin of safety. Diclazuril has been used to treat coccidial infections in other animals. The other class of medication used to treat EPM is pyrimethamine which actually kills the EPM organism. However, there are cases where the horse gets worse when treated with the pryimethamine as the protozoa die off and there is an inflammatory response.

One of the proposals to prevent EPM disease in the horse is to kill the EPM protozoa after it enters the horse’s body but before it makes it’s way into the nervous system. It takes about 4 days from ingestion of the infective stage of EPM organism to the transformation to the stage that enters of spinal cord and brain. If treatment is given every 4 days then the organism shouldn’t be able to cause damage to the nervous system. Since the horse is a dead end host for the EPM organism (i.e. the horse can’t pass the disease on to any other animal) this treatment should not lead to resistance.