I267L Is Neither the Virulence- Nor the Replication-Related Gene of African Swine Fever Virus and Its Deletant Is an Ideal Fluorescent-Tagged Virulence Strain

Abstract

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF) which reaches up to 100% case fatality in domestic pigs and wild boar and causes significant economic losses in the swine industry. Lack of knowledge of the function of ASFV genes is a serious impediment to the development of the safe and effective vaccine. Herein, I267L was identified as a relative conserved gene and an early expressed gene. A recombinant virus (SY18ΔI267L) with I267L gene deletion was produced by replacing I267L of the virulent ASFV SY18 with enhanced green fluorescent protein (EGFP) cassette. The replication kinetics of SY18ΔI267L is similar to that of the parental isolate in vitro. Moreover, the doses of 102.0 TCID50 (n = 5) and 105.0 TCID50 (n = 5) SY18ΔI267L caused virulent phenotype, severe clinical signs, viremia, high viral load, and mortality in domestic pigs inoculated intramuscularly as the virulent parental virus strain. Therefore, the deletion of I267L does not affect the replication or the virulence of ASFV. Utilizing the fluorescent-tagged virulence deletant can be easy to gain a visual result in related research such as the inactivation effect of some drugs, disinfectants, extracts, etc. on ASFV.

Comparison of Genotype II African Swine Fever Virus Strain SY18 Challenge Models

“…The ASFV SY18 strain, a genotype II virulent strain isolated from dead pigs in Shenyang, the site of the first ASF outbreak in China, is highly homologous to the classic challenge strain, ASFV Georgia 2007/1 (Gen-Bank: FR682468.2). IM infection of pigs with ASFV SY18 at 10 2.0 TCID 50 resulted in 100% mortality [16,18,20]. Our laboratory infected pigs with ASFV SY18 via IM at doses ranging from 1 TCID 50 to 10 4.0 TCID 50 during the course of developing a gene deletion vaccine, with no significant differences in disease duration (see Supplementary Materials Figure S2).…”

“…The details of three independent infection groups are shown in Table 1. The first group was a control group named IM200, in which three pigs were injected intramuscularly with 200 TCID 50 doses of ASFV SY18 (in 2 mL of cell culture medium) in the gluteal region, (the minimum intramuscular dose of the published ASFV SY18 challenge experiment (10 2.5 TCID 50 and 10 1.0 TCID 50 ) [16,20]). In the second group, nine pigs were equally divided into three subgroups (n = 3 each) and intranasally infected with ASFV SY18 at doses of 40, 200, and 1000 TCID 50 (in 2ml of cell culture medium).…”

Deletion of the B125R gene in the African swine fever virus SY18 strain leads to an A104R frameshift mutation slightly attenuating virulence in domestic pigs

“…For example, I267L deletion in the ASFV-GS isolate resulted in loss of virulence in pigs, whereas no effect was observed in the case of the ASFV-SY18 isolate. Moreover, H240R deletion in the ASFV-HLJ/2018 isolate resulted in a complete loss of virulence in pigs, in contrast to the ASFV-G isolate ( Ramirez-Medina et al, 2023 ; Ran et al, 2022 ; Zhang et al, 2021b ; Zhou et al, 2022 ). These discrepancies highlight the functional complexity of the ASF genome.…”

Vaccines for African swine fever: an update

“…Some ASFV genes’ mechanisms of action have been revealed, such as the MGF360-9L gene, which is involved in the down-regulation of interferon expression, and the I267L gene, which inhibits RNA Pol-III-RIG-I-mediated innate antiviral responses and leads to severe and lethal disease in animals vaccined ( Zhang et al, 2021a ; Ran et al, 2022 ; Zhang K. et al, 2022 ). Ramirez-Medina et al assessed the role of the MGF110-5L-6L gene during virus replication in cell cultures and experimental infection in swine in 2022 and showed that deletion of MGF110-5L-6L does not impact virulence or virus replication ( Ramirez-Medina et al, 2022a ).…”