Isolation of Porcine Bone Marrow Cells and Generation of Recombinant African Swine Fever Viruses

Transcription regulation of African swine fever virus: dual role of M1249L

African swine fever virus (ASFV), which poses significant risks to the global economy, encodes a unique host-independent transcription system. This system comprises an eight-subunit RNA polymerase (vRNAP), temporally expressed transcription factors and transcript associated proteins, facilitating cross-species transmission via intermediate host. The protein composition of the virion and the presence of transcription factors in virus genome suggest existence of distinct transcription systems during viral infection. However, the precise mechanisms of transcription regulation remain elusive. Through analyses of dynamic transcriptome, vRNAP-associated components and cell-based assay, the critical role of M1249L in viral transcription regulation has been highlighted. Atomic-resolution structures of vRNAP-M1249L supercomplex, exhibiting a variety of conformations, have uncovered the dual functions of M1249L. During early transcription, M1249L could serve as multiple temporary transcription factors with C-terminal domain acting as a switcher for activation/inactivation, while during late transcription it aids in the packaging of the transcription machinery. The structural and functional characteristics of M1249L underscore its vital roles in ASFV transcription, packaging, and capsid assembly, presenting novel opportunities for therapeutic intervention.

African swine fever virus NAM P1/95 is a mixture of genotype I and genotype VIII viruses

African swine fever virus causes a lethal hemorrhagic disease of domestic pigs. The NAM P1/1995 isolate was originally described as B646L genotype XVIII; however, full genome sequencing revealed that this assignment was incorrect.

Full genome sequence analysis of African swine fever virus isolates from Cameroon

African swine fever (ASF) is a devastating disease of domestic pigs that has spread across the globe since its introduction into Georgia in 2007. The etiological agent is a large double-stranded DNA virus with a genome of 170 to 180 kb in length depending on the isolate. Much of the differences in genome length between isolates are due to variations in the copy number of five different multigene families that are encoded in repetitive regions that are towards the termini of the covalently closed ends of the genome. Molecular epidemiology of African swine fever virus (ASFV) is primarily based on Sanger sequencing of a few conserved and variable regions, but due to the stability of the dsDNA genome changes in the variable regions occur relatively slowly. Observations in Europe and Asia have shown that changes in other genetic loci can occur and that this could be useful in molecular tracking. ASFV has been circulating in Western Africa for at least forty years. It is therefore reasonable to assume that changes may have accumulated in regions of the genome other than the standard targets over the years. At present only one full genome sequence is available for an isolate from Western Africa, that of a highly virulent isolate collected from Benin during an outbreak in 1997. In Cameroon, ASFV was first reported in 1981 and outbreaks have been reported to the present day and is considered endemic. Here we report three full genome sequences from Cameroon isolates of 1982, 1994 and 2018 outbreaks and identify novel single nucleotide polymorphisms and insertion-deletions that may prove useful for molecular epidemiology studies in Western Africa and beyond.

A protective multiple gene-deleted African swine fever virus genotype II, Georgia 2007/1, expressing a modified non-haemadsorbing CD2v protein

African swine fever virus is a complex DNA virus that causes high fatality in pigs and wild boar and has a great socio-economic impact. An attenuated genotype II strain was constructed by replacing the gene for wildtype CD2v protein with versions in which single or double amino acid substitutions were introduced to reduce or abrogate the binding to red blood cells and reduce virus persistence in blood. The mutant CD2v proteins were expressed at similar levels to the wildtype protein on the surface of infected cells. Three recombinant viruses also had K145R, EP153R, and in one virus DP148R genes deleted. Following immunization of pigs, the virus with a single amino acid substitution in CD2v, Q96R, induced moderate levels of replication, and 100% protection against virulent ASFV. Two additional recombinant viruses had two amino acid substitutions in CD2v, Q96R, and K108D, and induced no binding to red blood cells in vitro. In immunized pigs, reduced levels of virus in blood and strong early ASFV-specific antibody and cellular responses were detected. After challenge low to moderate replication of challenge virus was observed. Reduced clinical signs post-challenge were observed in pigs immunized with the virus from which DP148R gene was deleted. Protection levels of 83-100% were maintained across a range of doses. Further experiments with virus GeorgiaΔDP148RΔK145RΔEP153R-CD2v_mutantQ96R/K108D showed low levels of virus dissemination in tissue and transient clinical signs at high doses. The results support further evaluation of GeorgiaΔDP148RΔK145RΔEP153R-CD2v_mutantQ96R/K108D as a vaccine candidate.