“Equine protozoal myeloencephalitis (EPM) is a common cause of neurological disease of horses in North and South America, and results from a protozoal infection with Sarcocystis neurona or Neospora hughesi (less commonly),” stated Steve Reed, DVM, Dipl. ACVIM, of The Ohio State University (OSU), at the Western Veterinary Conference held Feb. 20-24 in Las Vegas, Nev. However, it might not be as common as was previously thought.

“Why bother EPM testing?” Reed asked the audience. While studies have shown the exposure rate of horses to S. neurona to be only about 52%, he said, many practitioners assume that nearly all horses have been exposed and elect to begin treating suspect cases rather than spending time and money on a test they think will be positive anyway.

“But what if that horse is seronegative (indicating no exposure to the parasite)?” he asked. “Do we spend hundreds if not thousands of dollars of the client’s money to treat a negative horse on a therapeutic trial?” he went on. “S. neurona<I> Western blot test (WBT) on (blood) serum is cheap and easy, with very few false negatives. With a very acute onset you might get a false negative, but there are very few of those.”

Although complete results are not yet available, Reed discussed an ongoing study of EPM exposure being conducted by OSU and Equine Biodiagnostics/IDEXX. The researchers evaluated serum WBT results in neurological patients presented for diagnosis from 2000-2003