African Swine Fever Virus MGF-110-9L-deficient Mutant Has Attenuated Virulence in Pigs Running title: The MGF-110-9L-gene-deleted ASFV is attenuated in swine

African swine fever virus (ASFV) is the etiological agent of African swine fever (ASF), an often lethal disease in domestic and wild pigs. ASF represents a major threat to the swine industry worldwide. Currently, no commercial vaccine is available because of the complexity of ASFV or biosecurity concerns. Live attenuated viruses that are naturally isolated or genetically manipulated have demonstrated reliable protection against homologous ASFV strain challenge. In the present study, a mutant ASFV strain with the deletion of ASFV MGF-110-9L (ASFV-Δ9L) was generated from a highly virulent ASFV CN/GS/2018 parental strain, a genotype II ASFV. Relative to the parental ASFV isolate, deletion of the MGF-110-9L gene significantly decreased the ability of ASFV-Δ9L to replicate in vitro in primary swine macrophage cell cultures. The majority of animals inoculated intramuscularly with a low dose of ASFV-Δ9L (10 HAD50) remained clinically