ANTIGENIC VARIANTS IN A PLAQUE-ISOLATE OF FOOT-AND-MOUTH-DISEASE VIRUS - IMPLICATIONS FOR VACCINE PRODUCTION

The occurrence of many subtypes within a serotype of foot-and-mouth di sease virus (FMDV) makes it difficult to control the disease by vaccin ation. Although inactivated vaccines are used successfully in many cou ntries, the appearance in the field of antigenic variants against whic h the vaccines do not confer protection is a constant problem in vacci ne manufacture. We had found previously a mixture of antigenic variant s in a field isolate of serotype A12. In this report we demonstrate th e presence of two variants in a plaque-isolate from this mixture. The second variant was detected only when the growth conditions were alter ed. Our observation points to the problems which may be encountered in the large scale growth of a virus for vaccine production.