Evaluation of an ASFV RNA Helicase Gene A859L for Virus Replication and Swine Virulence

Abstract

African swine fever virus (ASFV) is producing a devastating pandemic that, since 2007, has spread to a contiguous geographical area from central Europe to Asia. In July 2021, ASFV was detected in the Dominican Republic, the first report of the disease in the Americas in more than 40 years. ASFV is a large, highly complex virus harboring a large dsDNA genome that encodes for more than 150 genes. The majority of these genes have not been functionally characterized. Bioinformatics analysis predicts that ASFV gene A859L encodes for an RNA helicase, although its function has not yet been experimentally assessed. Here, we evaluated the role of the A859L gene during virus replication in cell cultures and during infection in swine. For that purpose, a recombinant virus (ASFV-G-∆A859L) harboring a deletion of the A859L gene was developed using the highly virulent ASFV Georgia (ASFV-G) isolate as a template. Recombinant ASFV-G-∆A859L replicates in swine macrophage cultures as efficiently as the parental virus ASFV-G, demonstrating that the A859L gene is non-essential for ASFV replication. Experimental infection of domestic pigs demonstrated that ASFV-G-∆A859L replicates as efficiently and induces a clinical disease indistinguishable from that caused by the parental ASFV-G. These studies conclude that the predicted RNA helicase gene A859L is not involved in the processes of virus replication or disease production in swine.

Evaluation of the Function of ASFV Gene E66L in the Process of Virus Replication and Virulence in Swine

“…This fact was consistent with the increased number of putative nonsynonymous mutations predicted between the two genetic groups. Interestingly, this situation contrasted with our previous predictions at, A859L [ 34 ], A151R [ 35 ], A104R [ 36 ], E165R [ 37 ], EP296R [ 38 ], and H108R [ 39 ], where variable dN/dS rates <1 were predicted; therefore, indicating that positive selection is the dominant force shaping the evolution of E66L gene.…”

“…Finally, to gain more insight into the evolution of the E66L gene in nature, we conducted a systematic evolutionary analysis as previously published for SARS-CoV-2 [ 32 ], and ASFV [ 33 , 34 , 35 , 36 ]. Analysis by the single-likelihood ancestor counting (SLAC) algorithm [ 33 ] revealed dN (synonymous substitution rate)/dS (nonsynonymous substitution rate) ratio = 1.21.…”

Deletion of African Swine Fever Virus Histone-like Protein, A104R from the Georgia Isolate Drastically Reduces Virus Virulence in Domestic Pigs

“…The molecular function of many of these genes remains undefined, with, at best, a predicted function based on sequence similarities to other virus or mammalian genes. Recent studies deleting single genes in the ASFV Georgia strain have resulted in varying phenotypes from undetectable or minor changes to virus growth in primary swine macrophages or in virulence (i.e., A859L [ 3 ], KP117R [ 4 ], MGF110-1L [ 5 ], X69R [ 6 ], MGF360-1L [ 7 ], and CD2 [ 8 ]).…”

Bayesian Phylodynamic Analysis Reveals the Dispersal Patterns of African Swine Fever Virus

“…However, despite the improvement reported in this study using the E183L gene as a target for the presented analysis, these results should be taken with caution, considering the still low correlation observed between the topologies displayed by the phylogenetic trees developed using full-length sequences and E183L. This low correlation can be clearly explained by the complex evolutionary process observed for different genes of ASFV [ 59 , 60 , 61 ]. In this context, we consider that further analysis should be performed using full-length sequences.…”