The first FDA-approved treatment for equine protozoal myeloencephalitis (EPM), Marquis, was launched Aug. 23 at Bayer’s headquarters in Kansas City, Mo. Robert MacKay, BVSc, PhD, Dipl. ACVIM, of the University of Florida College of Veterinary Medicine, discussed the knowledge, treatment, and prevention of EPM, which is the leading cause of neurologic problems in horses.

(For more on EPM, see https://thehorse.com/epm)

The Testing of Marquis

The new equine protozoal myeloencephalitis (EPM) treatment made by Bayer is a 15% ponazuril paste that kills several stages of Sarcocystis neurona, the causative parasite of the neurological disease. Ponazuril was proven to cross the blood-brain barrier and reach the horse’s central nervous system (spinal cord and brain) where the parasite resides. To complete its life cycle, the parasite must make its intermediate host neurologically unhealthy, thus causing it to become potential food for the opossum, where it completes its life cycle.

The horse is a dead-end host, meaning that the parasite can’t finish its life cycle in the horse. However, S. neurona can replicate (multiply) in the horse, thus increasing the number of parasites that cause damage. Marquis targets the energy metabolism of the parasite and disrupts its ability to reproduce, thus killing the multiplying stages of the parasite