While cerebrospinal fluid (CSF) testing for equine protozoal myloencephalitis (EPM) is widely regarded as the only definitive way to diagnose the disease, the difficult, expensive, and potentially dangerous test might not be necessary, according to new research from Colorado State University.

This study compared different testing schemes for EPM including assessment of the value of indirect fluorescent antibody testing (IFAT) of the combination of blood serum and CSF tests in relation to that of blood serum testing alone. In a previous study, using naturally exposed, experimentally infected, and vaccinated horses the researchers demonstrated that the IFAT has good accuracy in serum, and CSF correctly determined the infectious status of the horse more than 80% of the time.

The difficulty of diagnosing EPM is that a horse exposed to Sarcocystis neurona (the parasite that most frequently causes EPM) will retain antibodies whether the horse is actually displaying symptoms of EPM or not. The western blot test, which is currently the most accessible and affordable test for owners, can only return a positive or negative response. This has resulted in a number of false positives.

Indirect fluorescent antibody testing (IFAT) of either CSF or blood serum offers a higher specificity than the western blot. These tests can show not only the presence of antibodies to S neurona, but also quantify the concentration of antibodies, giving a far more specific result