It is called diclazuril and is still in the experimental stage in this country. Diclazuril, reported David E. Granstrom, DVM, PhD, BSc, Ohio State University and Gluck Equine Institute in Kentucky, and the author of a recently published book on EPM, is a member of the triazine antiprotozoal drug group. In a brief review of the disease, Granstrom told his listeners that the causative agent of EPM is Sarcocystis neurona, an organism that has a two-host life cycle. Opossums are the primary hosts and birds are the intermediate hosts. The horse is a dead end host for the organism and does not pass on the disease.
Current therapy involves long-term treatment with pyrimethamine and sulfonamides.
The treatment has been successful in numerous cases, but there have also been serious relapses. The mare could barely walk and was confined to her stall. After 11 days of diclazuril treatment, marked improvement was observed. Though there has been some permanent neurological damage, the mare has shown no signs of relapse in the one year since she was treated. He was in such serious condition that on the second day of treatment, he fell and had to be placed in a sling.