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Sensitivity and specificity of western blot testing of cerebrospinal fluid and serum for diagnosis of equine protozoal myeloencephalitis in horses with and without neurologic abnormalities

Barbara M. DaftCalifornia Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, San Bernardino Branch, San Bernardino, CA 92408.

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 DVM, DACVP
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Bradd C. BarrCentral Laboratory, Davis, CA 95616.

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 DVM, PhD, DACVP
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Ian A. GardnerDepartment of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616.

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 BVSc, PhD
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Deryck ReadCalifornia Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, San Bernardino Branch, San Bernardino, CA 92408.

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 DVM, PhD, DACVP
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William BellCalifornia Horse Racing Board, Ste 300, 1010 Hurley Way, Sacramento, CA 95825.

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Karen G. Peyser117 Palmetto Way, Irvine, CA 92612.

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Alex ArdansCentral Laboratory, Davis, CA 95616.

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Hailu KindeCalifornia Animal Health and Food Safety Laboratory System, School of Veterinary Medicine, University of California, Davis, San Bernardino Branch, San Bernardino, CA 92408.

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Jennifer K. MorrowEquine Biodiagnostics Inc, 1501 Bull Lea Rd, Ste 104, Lexington, KY 40511.

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 PhD

Abstract

Objective—To determine sensitivity and specificity of western blot testing (WBT) of CSF and serum for diagnosis of equine protozoal myeloencephalitis (EPM) in horses with and without neurologic abnormalities.

Design—Prospective investigation.

Animals—65 horses with and 169 horses without neurologic abnormalities.

Procedure—CSF and serum from horses submitted for necropsy were tested for Sarcocystis neuronaspecific antibody with a WBT. Results of postmortem examination were used as the gold standard against which results of the WBT were compared.

Results—Sensitivity of WBT of CSF was 87% for horses with and 88% for horses without neurologic abnormalities. Specificity of WBT of CSF was 44% for horses with and 60% for horses without neurologic abnormalities. Regardless of whether horses did or did not have neurologic abnormalities, sensitivity and specificity of WBT of serum were not significantly different from values for WBT of CSF. Ninety-four horses without EPM had histologic evidence of slight CNS inflammation.

Conclusions and Clinical Relevance—The low specificity of WBT of CSF indicated that it is inappropriate to diagnose EPM on the basis of a positive test result alone because of the possibility of false-positive test results. The high sensitivity, however, means that a negative result is useful in ruling out EPM. There was no advantage in testing CSF versus serum in horses without neurologic abnormalities. Slight CNS inflammation was common in horses with and without S neurona-specific antibodies in the CSF and should not be considered an indication of CNS infection with S neurona. (J Am Vet Med Assoc 2002;221:1007–1013)

Abstract

Objective—To determine sensitivity and specificity of western blot testing (WBT) of CSF and serum for diagnosis of equine protozoal myeloencephalitis (EPM) in horses with and without neurologic abnormalities.

Design—Prospective investigation.

Animals—65 horses with and 169 horses without neurologic abnormalities.

Procedure—CSF and serum from horses submitted for necropsy were tested for Sarcocystis neuronaspecific antibody with a WBT. Results of postmortem examination were used as the gold standard against which results of the WBT were compared.

Results—Sensitivity of WBT of CSF was 87% for horses with and 88% for horses without neurologic abnormalities. Specificity of WBT of CSF was 44% for horses with and 60% for horses without neurologic abnormalities. Regardless of whether horses did or did not have neurologic abnormalities, sensitivity and specificity of WBT of serum were not significantly different from values for WBT of CSF. Ninety-four horses without EPM had histologic evidence of slight CNS inflammation.

Conclusions and Clinical Relevance—The low specificity of WBT of CSF indicated that it is inappropriate to diagnose EPM on the basis of a positive test result alone because of the possibility of false-positive test results. The high sensitivity, however, means that a negative result is useful in ruling out EPM. There was no advantage in testing CSF versus serum in horses without neurologic abnormalities. Slight CNS inflammation was common in horses with and without S neurona-specific antibodies in the CSF and should not be considered an indication of CNS infection with S neurona. (J Am Vet Med Assoc 2002;221:1007–1013)