The most recent Journal of Parasitology contained an article that opens the door for battling equine protozoal myeloencephalitis (EPM). Researchers J. P. Dubey, BVSc, PhD, senior scientist at the Parasite Biology and Epidemiology Laboratory of the U.S. Department of Agriculture, William J. A. Saville, DVM, Dipl. ACVIM, assistant professor of the Department of Veterinary Preventive Medicine at The Ohio State University, and others found they could use the common domestic cat as the experimental intermediate host for the life cycle of the causative protozoal parasite Sarcocystis neurona.It already was known that the opossum is the definitive host, and the horse is an aberrant, intermediate host. The horse is considered to be a dead-end host (the parasite can't complete its life cycle in the horse, and a positive horse can't pass the parasite to another horse). This new breakthrough will allow researchers to complete the life cycle in the laboratory, thus allowing them to give EPM to horses in an experimental setting. This means that preventive vaccines and medical treatments for EPM can be challenged and proven effective or ineffective in the laboratory. Research needs to continue to determine if the cat is the natural intermediate host in the life cycle, or if there are others. Saville emphasized that: "At this point in time, cats should not be eliminated until the true natural intermediate host (or hosts) is determined."
It was stated in the article that, "EPM causes annual loss of more than $100 million to the equine industry in the United States." EPM causes mild to severe neurologic symptoms because the parasite migrates to the spinal cord and brain of horses.Current treatments can halt multiplication of the parasite in the horse, and future treatments (currently under FDA scrutiny) could kill the parasite in the horse. Most horses which test positive for antibodies to EPM do not develop clinical neurologic signs (toe dragging, drooped lip, lameness, incoordination, etc.). However, most horses which develop clinical signs do not recover to their previous level of athletic ability. A small percentage will recover, then relapse when treatments are halted. More Information on EPM
