Persistent domestic circulation of African swine fever virus in Tanzania, 2010-2017

Abstract

Background African swine fever (ASF) is a highly fatal viral hemorrhagic disease of domestic pigs that threatens livelihoods and food security. In Africa, ASF virus (ASFV) circulates in sylvatic (transmission between warthogs and soft argasid ticks) and domestic (transmission between domestic pigs) cycles, with outbreaks resulting from viral spill-over from sylvatic cycle. The present study investigated ASFV transmission patterns through virus genotyping. Results Genotypes II, IX, X, XV and XVI of ASFV were found to circulate and maintained by transmission between domestic pigs. Methods In addition to archived samples, tissue samples were collected from domestic pigs during outbreaks at different locations in Tanzania between 2015 and 2017 followed by nucleotide sequencing and phylogenetic analysis of B646L gene of ASFV. Conclusion Maintenance of ASFV in the domestic cycle was due to bleach of quarantine and transportation of affected pigs via major highways. Appropriate control measures including sanitary measures at the slaugher slabs and quarantine measures adherence are recommended to prevent ASF emergence and re-emergence in Tanzania. Transportation of pig and pig products for regional market should be controlled to prevent ASFV spreading to other states of the East African Community , as ASFV genotype II has spread beyond its geographical range.

African Swine Fever Virus Circulation between Tanzania and Neighboring Countries: A Systematic Review and Meta-Analysis

“…In addition, homology between ASFV strains from ticks collected at pig shelters and those from warthog burrows was observed, suggesting the possibility of ASFV transmission at the wild and domestic pigs interface [20]. Among countries included in this review, the ASFV p72 genotype II was described in Zambia [17,40], Mozambique [20,22,49], Tanzania [56,59,62], and in Malawi [63]. In 2007, the ASFV p72 genotype II escaped from its African geographical distribution to Georgia and subsequently spread to countries of the European Union and Russia before it reached Asia in August 2018 [13,25].…”

“…The genotype X was recovered from domestic pigs in 1950 in Kenya [15], since then, it was regularly reported to circulate and cause ASF outbreaks in Kenya [15,16,21,23], Uganda [21,23], Tanzania [22,23,61,62], Burundi [22,23,64], and DRC [51]. Recent molecular studies have reported high genetic similarity at three genomic regions of ASFV (p72, CVR and I73R-I329L) between the ASFV p72 genotype X strains responsible for ASF outbreaks in 2016 in Kagera region in Tanzania [62,64], the 2018 ASF outbreak in Rutana region in Burundi [64], and the ASF outbreak that occurred during December 2018 to January 2019 in South Kivu province of the DRC [51]. Commercial traffic and cross-border movements of domestic pigs and pork products were speculated as the main drivers of the ASFV spread between DRC, Burundi, and Tanzania [51,53,64].…”

“…The ASFV p72 genotype IX was recovered from domestic pigs and warthogs. This genotype is described as the most predominant in Uganda and Kenya [42], but also, it was described in DRC [50,53] and Tanzania [56,62]. Although associated with lethal ASF outbreaks [21,47,48], an increasing number of studies reported the genotype IX in asymptomatic domestic pigs in Tanzania [56], DRC [50], Uganda [44], and Kenya [65].…”

“…In 2007, the ASFV p72 genotype II escaped from its African geographical distribution to Georgia and subsequently spread to countries of the European Union and Russia before it reached Asia in August 2018 [13,25]. Additionally, the transboundary spread of the highly virulent ASFV p72 genotype II similar to the Georgia 2007/1 strain is highlighted by the introduction of this genotype into Tanzania probably from Malawi [59,62,63] and the emergence of this ASFV genotype in Zimbabwe in 2015 after several years of ASF absence probably from the neighboring Mozambique [68]. Furthermore, the genotype VIII was found to circulate in Zambia, Mozambique and Malawi [21][22][23], genotype XII was described in Zambia and Malawi [22], whilst genotype XV seems to be confined to Tanzania where both domestic and sylvatic cycles have been described for this genotype [22,57,58].…”

“…Mozambique 5[21] p72, p54, CVR V Domestic pig [22] p72 II, VIII Domestic pig [23] p72, CVR VI Domestic pig [20] p72, CVR, p30, p54 II, V, XXIV Tick [50] p72 [21] p72, p54, CVR IX Domestic pig [48] p72, p54, CVR, TK IX Domestic pig [55] p72, p54 IX Domestic pig [22] p72 I, X Warthog, domestic pig and bush pig [23] p72, CVR X Warthog [56] p72, p54, CVR, I73R-I329L II, IX Domestic pig Tanzania (9) [57] p72, p54, CVR XV Tick [58] p72, p54, CVR XV Domestic pig [59] p72 II Domestic pig [60] p72, p54, CVR X Domestic pig [61] p72 X Domestic pig [22] p72 X, XV, XVI Tick, warthog and domestic pig [23] p72, CVR X Warthog [62] p72 II, IX, X Domestic pig [63] p72, CVR, I73R-I329L II Domestic pig Malawi (4) [21] p72, p54, CVR V, VIII Domestic pig and tick [22] p72 VIII, V, XII Domestic pig [23] p72, CVR V, VIII Warthog and domestic pig [22] p72 X Domestic pig Burundi (3) [23] p72, CVR X Domestic pig [64] p72, CVR, I73R-I329L X Domestic pig ----Rwanda (0)…”