Construction of a Full-Length Infectious Clone Derived from Type O Foot-and-Mouth Disease Virus Isolated in South Korea for Vaccine Development with High Antigen Productivity

Background: Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-hoofed animals such as cattle and pigs, characterized by vesicular lesions in the mouth, nose, teats, and feet. Globally, the most commonly used FMD vaccines are inactivated vaccines produced by chemical inactivation of the infectious FMD virus (FMDV). This study aimed to establish an infectious clone of the O/Boeun/SKR/2017 virus that has demonstrated the highest antigen productivity among the various type O vaccine strains developed in South Korea to date. Methods: An infectious clone was generated from a type O virus isolated during the 2017 FMD outbreak in South Korea. The viral genome was divided into two fragments, each amplified separately, and subsequently ligated to produce a full-length infectious clone. Results: Rescue of infectious FMDV was confirmed using a commercial antigen detection kit and electron microscopy. Under optimized culture conditions, the rescued virus titer reached 2 × 107 TCID50/mL, and the antigen yield was 6.4 µg/mL. Following inactivation, the antigen was formulated into a vaccine and administered to pigs. Four weeks post-vaccination, challenge with the live virus resulted in no clinical symptoms, demonstrating complete protective efficacy. Conclusions: To the best of our knowledge, this is the first report describing the construction of an infectious clone derived from a field FMDV isolate in South Korea and its application in vaccine development. The O/Boeun/SKR/2017 infectious clone may serve as a genetic backbone for the rapid generation of new FMD vaccine candidates with high antigen productivity by substituting epitopes from other FMDV.