Abstract
BackgroundAfrican swine fever (ASF) is an infectious transboundary animal disease which causes high mortality, approaching 100% in domestic pigs and it is currently considered as the most serious constraint to domestic pig industry and food security globally. Despite regular ASF outbreaks within Malawi, few studies have genetically characterized the causative ASF virus (ASFV). This study aimed at genetic characterization of ASFV responsible for the 2019 outbreak in northern Malawi. The disease confirmation was done by polymerase chain reaction (PCR) followed by molecular characterization of the causative ASFV by partial genome sequencing and phylogenetic reconstruction of the B646L (p72) gene, nucleotide alignment of the intergenic region (IGR) between I73R and I329L genes and translation of the central variable region (CVR) coded by B602L gene.ResultsAll thirteen samples collected during this study in Karonga district in September 2019 were ASFV-positive and after partial genome sequencing and phylogenetic reconstruction of the B646L (p72) gene, the viruses clustered into ASFV p72 genotype II. The viruses characterized in this study lacked a GAATATATAG fragment between the I173R and the I329L genes and were classified as IGR I variants. Furthermore, the tetrameric amino acid repeats within the CVR of the B602L gene of the 2019 Malawian ASFV reported in this study had the signature BNDBNDBNAA, 100% similar to ASFV responsible for the 2013 and 2017 ASF outbreaks in Zambia and Tanzania, respectively.ConclusionsThe results of this study confirm an ASF outbreak in Karonga district in northern Malawi in September 2019. The virus was closely related to other p72 genotype II ASFV that caused outbreaks in neighboring eastern and southern African countries, emphasizing the possible regional transboundary transmission of this ASFV genotype. These findings call for a concerted regional and international effort to control the spread of ASF in order to improve nutritional and food security.
Highlights
African swine fever (ASF) is an infectious transboundary animal disease which causes high mortality, approaching 100% in domestic pigs and it is currently considered as the most serious constraint to domestic pig industry and food security globally
Laboratory confirmation of ASF All collected tissue samples belonging to 13 different domestic pigs from Karonga district included in the present study were positive for ASF virus (ASFV) after conducting diagnostic polymerase chain reaction (PCR) using ASFV-specific primers
Phylogenetic reconstruction of ASFV targeting B646L (p72) gene, tandem repeat sequences (TRS) and central variable region (CVR) In order to classify viruses characterized in this study among the 24 ASFV p72 known genotypes, the cterminal end of B646L (p72) gene was amplified and sequenced
Summary
African swine fever (ASF) is an infectious transboundary animal disease which causes high mortality, approaching 100% in domestic pigs and it is currently considered as the most serious constraint to domestic pig industry and food security globally. Despite regular ASF outbreaks within Malawi, few studies have genetically characterized the causative ASF virus (ASFV). The virus is transmitted through a sylvatic cycle involving warthogs (Phacochoerus africanus) which do not develop clinical disease and soft ticks of the Ornithodoros moubata complex inhabiting warthog burrows [4] This ancient sylvatic cycle specific to eastern and southern Africa occasionally leads to virus spill to domestic pigs through the tick-pig cycle that involves infected soft ticks dropped by warthogs at pig shelters [5]. The recent spread of ASF within Europe and Asia has substantially increased the global concern regarding the disease and it is considered as the most devastating disease to global domestic pig industry and food security [2]
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