Detection of the intergenic region III and multigene family 505 9R and 10R-V variant of African swine fever virus genotype II on pig farms in South Korea

African swine fever (ASF) is a significant infectious disease that affects only swine species. ASF was first reported on a pig farm in South Korea in September 2019. As of July 2024, 44 pig facilities and 4143 wild boars in South Korea have been confirmed to be positive for ASF, and ASF is now considered to be endemic in wild boar populations in this country. It is assumed that the infection spread sporadically to pig farms via biosecurity breaches, originating from a nearby source of the virus, probably infected wild boars. In this study, ASF samples collected from eight pig farms between July 2023 and July 2024 were subjected to genetic analysis. All analyzed ASF virus (ASFV) isolates belonged to the p72 and p54 genotype II, CD2v serogroup 8, and the central variable region type 1. Novel multigene family 505_9R/10R (MGF)-V variations were detected in four ASFV isolates from pig farms in the east-central region. Analysis of the intergenic region (IGR) between the I73R and I329L genes showed that three of four MGF-V variants belonged to the IGR-II type, while one isolate was an IGR-III variant. These results provide further insights into the genetic variation and evolution of ASFV spreading in South Korea, highlighting the need to enhance genetic surveillance of ASFV isolates circulating in the country.