The ELISA measures antigen-antibody binding qualitatively and quantitatively. SNT only tests for neutralizing antibodies, whereas the ELISA also tests for non-neutralizing antibodies. As opposed to SNT the antibody ELISA is less complicated and is therefore used in routine diagnostics. A number of commercially available test kits permit automatisation and supply results within a few hours. In areas where there is a low seroprevalence and vaccination is not permitted (e.g. Sweden), the antibody ELISA detects PI animals within a herd (the higher the antibody count is in a bulk milk sample the greater is the probability that there is a PI animal in the herd).

What is required?

• purified antigen (to test for or quantify antibodies)
• standardized solutions (positive or negative controls)
• sample to be tested
• micro titre plates
• rinsing fluid
• enzyme marked antibodies and enzyme substrate
• ELISA reader (spectrophotometer) for quantitative measurements