Antigenic variability of foot-and-mouth disease virus serotype O during serial cytolytic passage

The emergence and disappearance of antigenic variants of foot-and-mouth disease virus (FMDV) during a field outbreak occurs periodically due to the volatile nature of its genome. In the present analysis, change in antigenic behavior of serotype O FMDV during the serial cytolytic passage in the absence of immune pressure was observed. Initially, the isolate showed a poor antigenic match (relationship value <0.3) with the serotype O vaccine strain and upon serial passage increase in relationship value was observed. Comparison of capsid sequence revealed substitution at four positions (VP3:K₅₈ → E and P₁₅₈ → S, VP1:E₈₃ → K and R₁₇₂ → Q) acquired during the serial passage. Examination of passage level and amino acid substitution revealed the critical role of position VP3-58 that was identified earlier as crucial for antigenic site IV, in the observed antigenic variability. The role of position VP3-58 was further confirmed using reverse genetics approach.