From Equine Disease Quarterly, Funded by Underwriters at Lloyd’s, London, Brokers, and Their Kentucky Agents, https://www.uky.edu/Agriculture/VetScience/q_jan02/q-jan02.htm.

Equine Protozoal Myeloencephalitis (EPM) is an infectious, degenerative protozoal disease of the central nervous system of the horse. The causative agent of EPM has been identified as Sarcocystis neurona.  Dr. David Granstrom developed the first pre-mortem test for the presence of S. neurona antibodies in 1993, using a western blot immunoassay. This test is currently the most reliable test that can be performed on serum and cerebrospinal fluid to detect the presence of antibodies to S. neurona