Assessing the agreement of Western blot test results for paired serum and cerebrospinal fluid samples from horses tested for antibodies to Sarcocystis neuronaf.

This research article investigates the correlation between Western blot test results for the presence of antibodies to Sarcocystis neuronaf, a causative agent of a neurological disease in horses, in blood serum and cerebrospinal fluid (CSF). The study reveals a moderate level of agreement between the two types of test results, indicating the continued necessity of CSF testing in diagnosing equine protozoal myeloencephalitis (EPM).

Objectives and Methodology of the Research

• The aim of this research was to ascertain the correlation between the Western blot test results for antibodies to S. neurona in the serum and CSF of horses.
• The researchers analyzed the results for a series of 181 paired serum and CSF samples from horses suspected of having EPM. These samples were submitted to the Michigan State University Animal Health Diagnostic Laboratory for testing.
• The analysis evaluated the alignment of serum and CSF results across three possible outcomes: negative (no antibodies detected), positive (presence of antibodies), and suspect (test results unclear).
• An additional analysis was performed whereby the suspect samples were reclassified as negative, giving a result of a binary presence or absence of antibodies.

Results and Interpretation

• The agreement between the paired serum and CSF tests was determined using the kappa statistic, a measure of inter-rater agreement. For the samples classified as negative, positive, or suspect, the kappa statistic was 0.469. When the suspect results were reclassified as negative, the kappa statistic slightly increased to 0.474.
• The researchers observed that approximately 29% (33 out of 112) of the CSF samples from seropositive horses (those which were positive for S. neurona antibodies in the serum) tested negative.
• This finding indicates that the correlation between the serum and CSF test results is only moderate. Therefore, relying solely on serum testing may result in undetected cases of EPM.

Implications of the Research

• The moderate agreement between serum and CSF testing supports the ongoing use of CSF testing in suspected cases of EPM, even in seropositive horses.
• This research thus reinforces the need for comprehensive testing strategies that consider both blood and cerebrospinal fluid sample analysis to ensure an accurate EPM diagnosis.