Isolation of Variant Strains from Foot-and-Mouth Disease Virus Propagated in Cell Cultures Containing Antiviral Sera

SUMMARY: Three strains of foot-and-mouth disease virus of type SAT 1 were propagated serially in cultures of pig kidney cells in the presence of gradually increased concentrations of specific antiserum. All showed an increase in their ability to multiply in the presence of the serum. With two of the strains, complement-fixation tests revealed that propagation under these conditions was associated with modification of antigenic structure, but antigenic differences were detected later than changes in the ability of all strains to multiply in the presence of antiserum. Processes of this nature may possibly result in vivo from similar interactions of virus and antibody in host populations.