Pathological Characterization of African Swine Fever Viruses With Genetic Deletions Detected in South Korea

African swine fever virus (ASFV) genotype II has been circulating in South Korea, causing substantial economic losses to the Korean pig industry since 2019. Genetic epidemiological investigations using whole-genome sequencing have been conducted to track the genetic evolution of ASFV. Two ASFV strains were detected in domestic pig farms in South Korea, one with a large deletion in the MGF 360-6L gene and the other in the MGF 360-21R gene. Phylogenetic analysis indicated that all Korean isolates belonged to the Asian subgroup of ASFV genotype II and were further divided into distinct subclusters of Korean African swine fever (ASF) group I. To identify the pathological changes caused by the deletion of MGF 360-6L and MGF 360-21R genes, we evaluated their pathogenicity in experimentally infected domestic pigs. No significant changes in pathogenicity were observed compared to other viruses evaluated in our previous studies. All inoculated pigs died 7–10 days post-inoculation (dpi), showing acute forms of illness with common pathological lesions. These results highlight that large genetic deletions can occur naturally in ASFV, but the deletions in MGF 360-6L and MGF 360-21R genes did not alter pathogenicity in domestic pigs. Further research is needed to understand the roles of these genes, especially in viral replication and pathogenicity in wild boars and ticks.