An enzyme-linked immunosorbent assay (ELISA) for measurement of antibodies against equine herpesvirus 2 in equine sera.

This study outlines the development and effectiveness of an enzyme-linked immunosorbent assay (ELISA) for detecting antibodies against equine herpesvirus type 2 (EHV-2) in horse blood serum.

Development of the ELISA

• The researchers developed an indirect ELISA, a test that measures specific antibodies in a sample by using an antigen (a substance that induces an immune response) to attract them.
• The antigen used here was derived from equine herpesvirus type 2, a widespread virus affecting horses, whose presence the study aims to detect.
• The optimal conditions for the test like the amount of antigen used and the dilutions of serum (the liquid part of blood) and conjugate (a compound formed by combining two or more substances) necessary for accurate results were determined through chequerboard titrations – a method used to establish ideal experimental conditions by testing an array of dilutions against each other.

Comparison with the Virus Neutralization Test

• The ELISA was compared with the traditional virus neutralization (VN) test to assess its effectiveness.
• The VN test works by mixing the virus with a sample of serum from the patient. If antibodies against the virus are present in the serum, they will bind to the virus and stop it from infecting cells.
• Comparatively, the ELISA produced titers (measures of the amount of antibodies in serum) approximately 1500 times higher than the VN test, indicating a higher sensitivity in detection.
• The correlation between the ELISA results and VN test results was assessed on 42 equine serums, yielding a correlation coefficient (a statistical measure of similarity) of 0.815, which suggests a strong positive relationship between the results from both tests.
• All positive serum samples under the VN test appeared positive in the ELISA, and even one serum that tested negative in the VN test appeared positive in the ELISA. This implies that the ELISA could detect EHV-2 even in cases where the VN test did not.

Field Application of the ELISA

• When trialed in field conditions, the ELISA demonstrated its practicality by detecting increased antibody titers against EHV-2 in 13 out of 14 foals shortly after they began excreting the virus. This affirms the potential of the ELISA as a valuable diagnostic test in real-world settings.