Indirect fluorescent antibody testing of cerebrospinal fluid for diagnosis of equine protozoal myeloencephalitis.

The research investigates the effectiveness of using cerebrospinal fluid (CSF) testing with an indirect fluorescent antibody test (IFAT) for diagnosing equine protozoal myeloencephalitis (EPM), a disease in horses caused by the Sarcocystis neurona parasite. The study results indicate that while CSF testing can contribute to diagnosing EPM, its additional value is limited if a serum test has already been carried out.

Methodology

• The researchers performed indirect fluorescent antibody tests (IFAT) on 428 serum samples and 355 cerebrospinal fluid (CSF) samples taken from 182 horses.
• The horses in this study were either naturally exposed to the parasite causing EPM, experimentally infected, or vaccinated.
• EPM diagnosis was confirmed based on histologic examination of the central nervous system (CNS).
• They fitted probability distributions to the serum IFAT results in EPM-positive and EPM-negative horses, and then modeled the correlation between serum and CSF results.

Results

• The study found that post-test probabilities of EPM increased as the IFAT serum and CSF titers went up.
• Differences in post-test probabilities when using a serum-CSF combination test and a serum test only were less than or equal to 19% in 95% of simulations.
• The biggest increases were seen when serum titers range from 40 to 160 and pre-test probabilities were from 5% to 60%.
• In all simulations, the difference between pre- and post-test probabilities was greater for a CSF test alone, compared to a serum test only.

Conclusions

• The research concludes that, while CSF testing can contribute to diagnosing EPM, its additional value is limited if a serum test has already been carried out.
• CSF testing might be used alone when CSF is required for other procedures.
• The study also highlights the importance of ruling out other causes of neurologic disease to reduce the necessity of additional EPM testing.