The neurologic disease equine protozoal myeloencephalitis (EPM) is notoriously difficult to confirm with bloodtests. This is because many horses have been exposed to Sarcocystis neurona, one of EPM’s causative parasites and, so, have blood serum antibodies against the pathogen. Also, there’s no such thing as a “textbook” EPM case, as far as clinical signs go, and a variety of conditions besides S. neurona infection can cause neurologic illness, complicating the diagnostic picture.

These limitations mean veterinarians are always looking for adjunct tests to add to their diagnostic arsenal. Recently, in two separate studies, Amy Johnson, DVM, Dipl. ACVIM, of the University of Pennsylvania School of Veterinary Medicine’s New Bolton Center, in Kennett Square, and Steve Reed, DVM, Dipl. ACVIM, of Rood & Riddle Equine Hospital in Lexington, Kentucky, investigated whether acute phase proteins (APPs) could serve as EPM markers. They presented the results of their work at the Second EPM Workshop, held Oct. 25-27, 2017, in Tahoe City, California.

“One of the big problems with EPM diagnosis is the discrepancy between the high seroprevalence and the very low incidence of clinical disease,” said Johnson. In fact, most horses with evidence of exposure never get sick. Then, for the horses that do, the gold standard for diagnostic confirmation is a combination of true neurologic signs of disease, exclusion of other potential causative diseases, and evidence of intrathecal antibody production—that is, antibodies against S. neurona produced within the nervous system.

“Acute-phase proteins are produced by the liver and are known to rise very rapidly in response to infection and inflammation,” she said, and could potentially be used in concert with blood tests—which alone produce a lot of false positives. The New Bolton research team, led by Neil Mittelman, DVM, an internal medicine resident, looked at the two most commonly studied APPs: C-reactive protein (CRP) and serum amyloid A (SAA)