E62 - Evaluation of Real-time PCR for the Identification of Sarcocystis neurona in Equine Cerebrospinal Fluid

Background: Equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona remains an ante-mortem diagnostic challenge for some horses. Recent work suggested the use of real-time PCR (rtPCR) on cerebrospinal fluid (CSF) as a promising diagnostic tool. 

Objective: To evaluate the sensitivity and specificity of S. neurona rtPCR on CSF for EPM diagnosis from horses with EPM and S. neurona-seropositive horses with other neurologic conditions.

Animals: 99 horses with neurologic disease that underwent complete neurologic examination, cerebrospinal fluid collection, and, if euthanized, neurologic necropsy. 

Methods: Retrospective case-control study using biobanked CSF samples. CSF samples from neurologic horses with post-mortem confirmed EPM diagnosis, presumptive EPM diagnosis using strict criteria (SnSAG 2, 4/3 ELISA serum:CSF titer ratios < 50) and horses diagnosed with other neurologic diseases were used.

Results: There were 52 horses with EPM; 23 were confirmed on post-mortem exam, and 29 were presumptive clinical diagnoses. The other 47 horses all had post-mortem confirmed diagnoses of other neurologic diseases including equine degenerative myeloencephalopathy (EDM), cervical vertebral stenotic myelopathy, trauma, and others. CSF samples from all horses were tested for S. neurona via rtPCR. One CSF sample was weakly positive for S. neurona by rtPCR, this sample was obtained from a horse with confirmed EDM. CSF samples from the other 98 horses were negative for S. neurona by rtPCR. 

Conclusions and clinical importance: The results from this study contradict previous conclusions that S. neurona rtPCR is potentially useful for EPM diagnosis, as they indicate that it has a low sensitivity (0%) for EPM.