Antigenic variation in foot-and-mouth disease: studies based on the virus neutralization reaction

The neutralization reaction is the most appropriate in vitro reference test system for assessing intratypic antigenic variation as it involves the antigenic determinants responsible for virus strain specificity and evoking protective antibody. Antigenic relationships determined in different neutralization test systems were independent of the system used and were assumed to truly reflect antigenic variation. The two-dimensional microneutralization test was found to be appropriate for foot and mouth disease (FMD) virus strain differentiation. To minimize test to test variation, comparisons are performed as matched pairs. The pooled variance of the test system is used to assess the significance of the relationships obtained. Antisera from convalescent animals were less specific than those from vaccinates. Serum quality seemed less critical for the virus neutralization than the complement fixation reaction. A system for FMD virus strain differentiation based on the use of the virus neutralization reaction taking into account the statistical and biological significance of observed r values is recommended.