Abstract
BackgroundAfrican swine fever (ASF) is a highly contagious and severe hemorrhagic viral disease of domestic pigs. The analysis of variable regions of African swine fever virus (ASFV) genome led to more genotypic and serotypic information about circulating strains. The present study aimed at investigating the genetic diversity of ASFV strains in symptomatic pigs in South Kivu province of the Democratic Republic of Congo (DRC).Materials and methodsBlood samples collected from 391 ASF symptomatic domestic pigs in 6 of 8 districts in South Kivu were screened for the presence of ASFV, using a VP73 gene-specific polymerase chain reaction (PCR) with the universal primer set PPA1-PPA2. To genotype the strains, we sequenced and compared the nucleotide sequences of PPA-positive samples at three loci: the C-terminus of B646L gene encoding the p72 protein, the E183L gene encoding the p54 protein, and the central hypervariable region (CVR) of the B602L gene encoding the J9L protein. In addition, to serotype and discriminate between closely related strains, the EP402L (CD2v) gene and the intergenic region between the I73R and I329L genes were analyzed.ResultsASFV was confirmed in 26 of 391 pigs tested. However, only 19 and 15 PPA-positive samples, respectively, were successfully sequenced and phylogenetically analyzed for p72 (B646L) and p54 (E183L). All the ASFV studied were of genotype X. The CVR tetrameric repeat clustered the ASFV strains in two subgroups: the Uvira subgroup (10 TRS repeats, AAAABNAABA) and another subgroup from all other strains (8 TRS repeats, AABNAABA). The phylogenetic analysis of the EP402L gene clustered all the strains into CD2v serogroup 7. Analyzing the intergenic region between I73R and I329L genes revealed that the strains were identical but contained a deletion of a 33-nucleotide internal repeat sequence compared to ASFV strain Kenya 1950.ConclusionASFV genotype X and serogroup 7 was identified in the ASF disease outbreaks in South Kivu province of DRC in 2018–2019. This represents the first report of ASFV genotype X in DRC. CVR tetrameric repeat sequences clustered the ASFV strains studied in two subgroups. Our finding emphasizes the need for improved coordination of the control of ASF.
Highlights
African swine fever (ASF) is a highly contagious and severe hemorrhagic viral disease of domestic pigs
Analyzing the intergenic region between I73R and I329L genes revealed that the strains were identical but contained a deletion of a 33nucleotide internal repeat sequence compared to African swine fever virus (ASFV) strain Kenya 1950
ASFV genotype X and serogroup 7 was identified in the ASF disease outbreaks in South Kivu province of Democratic Republic of Congo (DRC) in 2018–2019
Summary
African swine fever (ASF) is a highly contagious and severe hemorrhagic viral disease of domestic pigs. Distinct antigenic types of ASFV were identified based on haemadsorption inhibition (HAI) serological typing, where ASF protective immunity was shown to be serotype-specific, and viruses belonging to identical serogroups cross-protected against each other [20]. This has significant importance for vaccine development. The CD2V protein, encoded by the ASFV EP402R gene, is a transmembrane glycoprotein located in the viroplasm (around viral factories) and in the plasma membrane of infected cells It is among the most variable genes in the ASFV genome [21, 22]. Haemadsorption involves adhesion of pig erythrocytes to the surface of ASFV infected cells, a key requirement is expression of CD2v in ASFV-infected cells [20]
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