Cross-reactions of normal bovine serums to foot-and-mouth disease virus in plaque-reduction neutralization and radial immunodiffusion.

Serums from 150 cattle with no known exposure to foot-and-mouth disease (FMD) virus were tested by both the plaque-reduction neutralization (PRN) technique and the radial immunodiffusion (RID) technique to evaluate the significance and the extent of cross-reactions in these tests. Serums from 30 cattle from each of 5 locations were tested against representative viruses of each of the 7 types of FMD virus. High levels of cross-reactions with both the RID and PRN techniques were found in serums of specific groups. Higher levels of cross-reactions were noted for Asia, SAT I, SAT II, and SAT III than for A, O, or C viruses with the PRN technique, and higher levels for SAT II and SAT III with the RID technique. The reactions for most serums appeared to be quite specific; a given serum was often reactive with only 1 or 2 viruses.