Analysis of novel African swine fever variants circulating in wild boars in South Korea isolated in 2021 by deep sequencing

Abstract

African swine fever (ASF) is major infectious disease of concern currently circulating in swine species, causing high mortality and significant economic damage on the global scale. Since the first incident of ASF outbreak in Korea in 2019, the disease has continued to spread throughout the country despite enhanced biosecurity measures, with wild boars playing a key role. Thus, characterizing the domestic African swine fever virus (ASFV) strains including its genetic variants is crucial for both monitoring and diagnostic purposes. In this study, we sequenced and analyzed the full genome of seven Korean ASFV strains isolated from ASFV positive wild boar samples collected in 2021 from various regions. The sequences were compared with previously isolated ASFV strains to track the origin and the evolutionary trend of the ASFV variants residing in the wild boar population in Korea. A total of thirty single-nucleotide polymorphisms (SNPs) were detected which consists of ten synonymous and eighteen non-synonymous mutations, a single mutation at intergenic region (IGR), and a truncation mutation which led to a premature stop codon. Out of the mutations, thirteen were present in the MGF 505-9R gene. All seven strains contained an additional ten-nucleotides (nt) long tandem repeat sequence (TRS) between the I73R and I179L gene, similar to strains previously studied in Korea. Additionally, a new seventeen-nt long tandem repeat sequence insertion, adjacent to the MGF 505-10R, has been observed at the IGR between the MGF 505-9R and 10R genes. The results of the study provide extra insight for characterizing the ASFV virus in Korea and suggesting new molecular genetic markers for epidemiological monitoring, thus minimizing the risk of new ASF outbreaks in Korea.