2010 ACVIM late breaking research talk neurology session

NEW QUANTITATIVE ASSAYS FOR THE DIFFERENTIAL DIAGNOSIS OF EQUINE PROTOZOAL MYELOENCEPHALITIS (EPM).  SM Reed1, DK Howe2, MR Yeargan2,    JK Morrow3, AJ Graves3 and WJA Saville4. 1. Rood and Riddle Equine Hospital, Lexington, KY.  2. University of Kentucky, Lexington, KY. 3. Equine Diagnostic Solutions, Lexington, KY. 
4. The Ohio State University, Columbus, OH.

A field study was conducted on neurologic horses to evaluate new quantitative assays and to re-establish the importance of performing cerebrospinal fluid (CSF) taps for accurate diagnosis of EPM.

Two new ELISAs, designed to be run concurrently, have been developed at the Gluck Equine Research Center.  These assays incorporate three unique antigens of Sarcocystis neurona to measure the IgG response to parasite infection.   Paired serum and CSF samples collected from 131 clinical cases examined at Rood and Riddle Equine Hospital (RREH) over the past three years were tested with the two complementary assays.  The ELISA results were compared to standard WB results performed at Equine Diagnostic Solutions (EDS) laboratory.   Neurologic status was monitored at presentation and on follow-up examination for most patients. Histopathological results were available for 14 horses with paired samples and another 5 horses with only CSF available.

Qualitative WB and quantitative ELISA results, clinical histories and outcomes, and necropsy results (where available) were tabulated. Cases were grouped by diagnosis into EPM, CVM and other, and the compiled data were then analyzed.  Strong correlation was observed between ELISA and WB results. Endpoint serum titers alone were not predictive of an EPM diagnosis.  However, endpoint CSF titers were correlated strongly with an EPM diagnosis. Furthermore, a serum-to-CSF titer ratio was the most informative criterion for the differential diagnosis, consistent with antigen-specific antibody indices that are used for determining intrathecal antibody production.  Serum:CSF ratios <100 were observed for 83% (24/29) of EPM cases, while 97% (36/37) of CVM diagnoses and 88% (57/65) of other neurologic diagnoses had serum:CSF ratios of >100.  In total, the serum:CSF titer ratio obtained with the new ELISAs provided an accurate diagnosis for 89% (117/131) of these neurologic cases.  Importantly, a 1:1000-titer blood sample spiked into pristine CSF had no appreciable effect on ELISA results until there was greater than 10,000 red cells per microliter, thereby demonstrating the utility of these assays even when there is significant blood contamination.

This study verified that analysis of both serum and CSF from horses suspected to have EPM is more beneficial than examination of serum alone. The results support the use of these quantitative assays as valuable new tools for the diagnosis of EPM in horses showing clinical signs.

Last Updated on Thursday, 16 September 2010 15:31
 
2010 ACVIM late breaking research talk neurology session

NEW QUANTITATIVE ASSAYS FOR THE DIFFERENTIAL DIAGNOSIS OF EQUINE PROTOZOAL MYELOENCEPHALITIS (EPM).  SM Reed1, DK Howe2, MR Yeargan2,    JK Morrow3, AJ Graves3 and WJA Saville4. 1. Rood and Riddle Equine Hospital, Lexington, KY.  2. University of Kentucky, Lexington, KY. 3. Equine Diagnostic Solutions, Lexington, KY. 
4. The Ohio State University, Columbus, OH.

A field study was conducted on neurologic horses to evaluate new quantitative assays and to re-establish the importance of performing cerebrospinal fluid (CSF) taps for accurate diagnosis of EPM.

Two new ELISAs, designed to be run concurrently, have been developed at the Gluck Equine Research Center.  These assays incorporate three unique antigens of Sarcocystis neurona to measure the IgG response to parasite infection.   Paired serum and CSF samples collected from 131 clinical cases examined at Rood and Riddle Equine Hospital (RREH) over the past three years were tested with the two complementary assays.  The ELISA results were compared to standard WB results performed at Equine Diagnostic Solutions (EDS) laboratory.   Neurologic status was monitored at presentation and on follow-up examination for most patients. Histopathological results were available for 14 horses with paired samples and another 5 horses with only CSF available.

Qualitative WB and quantitative ELISA results, clinical histories and outcomes, and necropsy results (where available) were tabulated. Cases were grouped by diagnosis into EPM, CVM and other, and the compiled data were then analyzed.  Strong correlation was observed between ELISA and WB results. Endpoint serum titers alone were not predictive of an EPM diagnosis.  However, endpoint CSF titers were correlated strongly with an EPM diagnosis. Furthermore, a serum-to-CSF titer ratio was the most informative criterion for the differential diagnosis, consistent with antigen-specific antibody indices that are used for determining intrathecal antibody production.  Serum:CSF ratios <100 were observed for 83% (24/29) of EPM cases, while 97% (36/37) of CVM diagnoses and 88% (57/65) of other neurologic diagnoses had serum:CSF ratios of >100.  In total, the serum:CSF titer ratio obtained with the new ELISAs provided an accurate diagnosis for 89% (117/131) of these neurologic cases.  Importantly, a 1:1000-titer blood sample spiked into pristine CSF had no appreciable effect on ELISA results until there was greater than 10,000 red cells per microliter, thereby demonstrating the utility of these assays even when there is significant blood contamination.

This study verified that analysis of both serum and CSF from horses suspected to have EPM is more beneficial than examination of serum alone. The results support the use of these quantitative assays as valuable new tools for the diagnosis of EPM in horses showing clinical signs.

Last Updated on Thursday, 16 September 2010 15:31