Identification of L11L and L7L as virulence-related genes in the African swine fever virus genome

Introduction: African swine fever (ASF) is an infectious disease that causes considerable economic losses in pig farming. The agent of this disease, African swine fever virus (ASFV), is a double-stranded DNA virus with a capsid membrane and a genome that is 170-194 kb in length encoding over 150 proteins. In recent years, several live attenuated strains of ASFV have been studied as vaccine candidates, including the SY18 Delta L7-11. This strain features deletion of L7L, L8L, L9R, L10L and L11L genes and was found to exhibit significantly reduced pathogenicity in pigs, suggesting that these five genes play key roles in virulence. Methods: Here, we constructed and evaluated the virulence of ASFV mutations with SY18 Delta L7, SY18 Delta L8, SY18 Delta L9, SY18 Delta L10, and SY18 Delta L11L. Results: Our findings did not reveal any significant differences in replication efficiency between the single-gene deletion strains and the parental strains. Pigs inoculated with SY18 Delta L8L, SY18 Delta L9R and SY18 Delta L10L exhibited clinical signs similar to those inoculated with the parental strains. Survival rate of pigs inoculated with 10(3.0)TCID(50) of SY18 Delta L7L was 25%, while all pigs inoculated with 10(3.0)TCID(50) of SY18 Delta L11L survived, and 50% inoculated with 10(6.0)TCID(50) SY18 Delta L11L survived. Discussion: The results indicate that L8L, L9R and L10L do not affect ASFV SY18 virulence, while the L7L and L11L are associated with virulence.