Solving EPM

What Is EPM?: The History

Equine protozoa myeloencephalitis (EPM) is a progressive neurologic disease of horses found in both North and South America. The disease was first identified by in 1964 by J.R. Rooney, who recognized the protozoa in spinal cord lesions in Standardbreds (Rooney as cited in MacKay, 1997). Similar lesions were also identified by R.Macruz in Brazil around the same time (Macruz as cited in MacKay, 1997). Since this time, EPM has appeared in most of the lower 48 states as well as Panama and Canada with some "unofficial" reports from Venezuela, Argentina, and Mexico.
When this protozoa was first isolated it was thought to be Toxoplasma gondii, a microorganism which characteristically produces lesions. However, in 1974, J.P.Dubey (1974) was able to culture an organism from an infected horse and found it to be Sarcocystis (Dubey (1974) as cited in MacKay, 1997). This genus is named for its terminal developmental stage, sarcocyst, that is found in the striated muscle (i.e. skeletal muscle) of the intermediate host. The organism was named Sarcocystis neurona due to the fact that it usually develops within the neurons (EPM Seminar, University of Missouri, 1995).