Characterization of a Virus Rescued from a Full-Length Infectious Clone Derived from the Type A Foot-and-Mouth Disease Virus Isolated in South Korea

Foot-and-mouth disease (FMD), a vesicular disease, causes lesions in the mouth, nose, teats, and feet of cloven-hoofed animals. Vaccination remains the most effective method to prevent FMD outbreaks. Since 2010, South Korea has implemented nationwide vaccination and developed multiple domestic vaccine strains to achieve vaccine self-sufficiency. Here, we aimed to construct an infectious clone using the A/SKR/Yeoncheon/2017 virus, which exhibits the highest antigen productivity among previously developed vaccine strains. An infectious clone was constructed based on the A/Yeoncheon/SKR/2017 virus isolated during an FMD outbreak in Korea in 2017. The viral genome was amplified in two fragments and assembled into a full-length clone, from which infectious recombinant virus was successfully rescued. The rescued virus was confirmed via serotyping and transmission electron microscopy to exhibit canonical 25–30 nm icosahedral morphology. Under optimized culture conditions using suspension-adapted BHK-21 cells (multiplicity of infection 0.001; 12 h post-infection), the recombinant virus achieved titers of 108 TCID50/mL and produced 6.2 μg/mL of 146S antigen, comparable to its parental counterpart. The experimental vaccine formulated with the rescued virus (15 μg/dose), 1% saponin, 1% aluminum hydroxide gel, and ISA 206 VG, induced protective immunity in eight-week-old pigs, with vaccinated animals exhibiting no clinical signs following homologous challenge. To our knowledge, this study represents the first successful construction of an infectious clone derived from a field-isolated serotype A FMDV in South Korea. In the future, this A/SKR/Yeoncheon/2017 infectious clone can serve as a platform backbone for the rapid development of next-generation, high-yield vaccine seed strains through targeted epitope exchange.