Establishment of a statistical base for use of ELISA in diagnostic serology for infectious bovine rhinotracheitis

The critical statistical parameters of an enzyme-linked immunosorbent assay were determined to enable quantitation of antibody responses in cattle affected with infectious bovine rhinotracheitis. A system of controlling well-to-well variations in optical density reading across a microtitre plate was evolved and dose--response assays were carried out to determine the dilution of serum which gave the greatest discrimination between acute and convalescent sera from an infected animal. Use of a standard serum was studied in further assays. An increase in optical density value of 0.15 was set as a diagnostic criterion for a significantly rising antibody response. This compared well with the conventional criterion of a fourfold rise in virus neutralizing antibody titre.