Detection of foot-and-mouth disease virus antibodies. II. Use of fractionated bovine antisera for improving the specificity of a "passive" hemagglutination test.

Because 7S immunoglobulin (Ig) G antibodies of low type specificity were present in mixtures with highly specific 19S IgM antibodies, many bovine antisera to foot-and-mouth disease virus (FMDV) type A(12), strain 119 cross-reacted with type O of FMDV and to some degree with type C in the passive hemagglutination (HA) test. After 19S IgM antibodies were separated by density gradient centrifugation or precipitated with 4% (w/v) polyethylene glycol, the antigen could be determined with "block" HA tests. Such tests used several antigen concentrations in the titration of each antiserum. Adding 4% (w/v) polyethylene glycol to the serum was especially convenient for rapid precipitation of 19S IgM antibodies for the test. Similar results were obtained with bovine 19S IgM antibodies to FMDV type O, subtype 1, strain Caseros and type C strain Rezende.