Equine protozoal myeloencephalitis: Etiology, diagnosis and treatment
EPM is seen any time of year, with an estimated 50 percent of horses exposed to S. neurona, though less than 1 percent develop clinical EPM. Although there's a low incidence of EPM in the general horse population, 14 cases per 10,000 horses per year (23 percent of the horses that died with neurologic signs) showed S. neurona antibodies in their CNS, according to studies done at the University of California-Davis (UC Davis).1
History of research
EPM has been studied since the 1970s. An early pioneer was J.P. Dubey, PhD, a parasitologist and now adjunct professor at the Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg Va., and Animal Parasitic Diseases Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, Md. Dubey, who did this work while at The Ohio State School of Medicine, was one of the early scientists to recognize EPM. It was initially described by James Rooney, DVM, and colleagues at the University of Pennsylvania as an unusual neurologic syndrome, then called segmental myelitis.
Since then, it's been reported in horses from 2 months to 24 years old, typically affecting horses 1 to 6 years of age.2 EPM is common in Thoroughbreds, Standardbreds and Quarter horses. It's also been found in ponies, but not in mules, donkeys or other nonhorse equids.