The Epidemiology of African Swine Fever in “Nonendemic” Regions of Zambia (1989–2015): Implications for Disease Prevention and Control

Abstract

African swine fever (ASF) is a highly contagious and deadly viral hemorrhagic disease of swine. In Zambia, ASF was first reported in 1912 in Eastern Province and is currently believed to be endemic in that province only. Strict quarantine measures implemented at the Luangwa River Bridge, the only surface outlet from Eastern Province, appeared to be successful in restricting the disease. However, in 1989, an outbreak occurred for the first time outside the endemic province. Sporadic outbreaks have since occurred almost throughout the country. These events have brought into acute focus our limited understanding of the epidemiology of ASF in Zambia. Here, we review the epidemiology of the disease in areas considered nonendemic from 1989 to 2015. Comprehensive sequence analysis conducted on genetic data of ASF viruses (ASFVs) detected in domestic pigs revealed that p72 genotypes I, II, VIII and XIV have been involved in causing ASF outbreaks in swine during the study period. With the exception of the 1989 outbreak, we found no concrete evidence of dissemination of ASFVs from Eastern Province to other parts of the country. Our analyses revealed a complex epidemiology of the disease with a possibility of sylvatic cycle involvement. Trade and/or movement of pigs and their products, both within and across international borders, appear to have been the major factor in ASFV dissemination. Since ASFVs with the potential to cause countrywide and possibly regional outbreaks, could emerge from “nonendemic regions”, the current ASF control policy in Zambia requires a dramatic shift to ensure a more sustainable pig industry.

Current status and evolving approaches to African swine fever vaccine development

“…Recently, ASF has emerged in Asia, including China (Zhou et al, ), and is rapidly spreading to many regions of the country (Li & Tian, ). Currently, ASF continues to be a huge burden to the pig industry in the affected areas (Costard et al, ; Simulundu et al, ; Zhou et al, ). ASF has a varied range of clinical pictures including acute, subacute, chronic and unapparent forms in domestic pigs, and mild or persistent infections in bushpigs and warthogs (Blome, Gabriel, & Beer, ; Sánchez‐Vizcaíno, Mur, Gomez‐Villamandos, et al, ).…”

Epidemiology of African swine fever in Africa today: Sylvatic cycle versus socio‐economic imperatives

“…The discovery of a cycle of maintenance and transmission of ASFV between domestic pigs and O. moubata complex ticks in the Mchinji district in Malawi revealed a pig population with improved resistance to the pathogenic effects of ASFV and the ability of the disease to persist without involvement of wild suids (Haresnape & Mamu, 1986;Haresnape et al, 1985Haresnape et al, , 1987. Similarly resistant populations of domestic pigs have been reported in Kenya (Okoth et al, 2012), along the Kenya/Uganda border on both sides (Abworo et al, 2017;Thomas et al, 2016); Mozambique (Penrith et al, 2007;Pen-rith, Thomson, Bastos, Phiri, et al, 2004) and the Eastern Province of Zambia (Simulundu et al, 2017). The involvement of ticks in these populations has not been documented and requires further investigation.…”

African swine fever: Update on Eastern, Central and Southern Africa

“…Kenya, Malawi, Mozambique, Tanzania, Uganda and Zambia have experienced multiple to frequent outbreaks (Table ). The endemic occurrence of ASF in domestic pigs has subsequently been documented in several Eastern African countries: Kenya (Gallardo, Ademun, et al, ; Gallardo, Okoth, et al, ; Lichoti et al, ; Okoth et al, ), Madagascar (Randrianantoandro, Kono, & Kubota, ; Ravaomanana et al, , ; Roger, Ratovonjato, Vola, & Uilenberg, ), Malawi (Haresnape, Lungu, & Mamu, , ); Mozambique (Penrith et al, , ; Quembo et al, ), Tanzania (Misinzo et al, ; Wambura, Masambu, & Msami, ), Uganda (Atuhaire, Afayoa, Ochwo, Mwesigwa, Okuni, et al, ; Barongo et al, ; Gallardo, Ademun, et al, ; Muhangi et al, ; Muwonge et al., ) and the Eastern Province of Zambia (Samui, Mwanaumo, & Chizyuka, ; Samui et al, ; Simulundu et al, , ; Wilkinson et al, ).…”

“…The warthog–tick cycle has been demonstrated in Kenya, Malawi, Mozambique, Tanzania, Uganda, Zambia and Zimbabwe (Plowright et al, ; Quembo et al, ). Spill‐over from the warthog–tick cycle to domestic pigs has been reliably reported from Kenya and Zimbabwe and is suspected to occur in areas where there is an interface between warthogs and domestic pigs in Mozambique, Tanzania, Uganda and Zambia (Kukielka et al, ; Quembo et al, ; Simulundu et al, ). Investigations in Malawi suggested that warthogs would play at best a minor role in ASF in domestic pigs because they were restricted to conservation areas distant from pig farming areas (Haresnape, Wilkinson, & Mellor, ).…”

“…On the contrary, the disease has devastating socio‐economic consequences in domestic pigs due to its high lethality. A domestic pig–tick cycle between domestic pigs and Ornithodoros ticks that live in their shelters (pig–tick cycle) has been demonstrated in Malawi and Mozambique and may be more widespread (Haresnape, Lungu, & Mamu, , ; Quembo, Jori, Heath, Pérez‐Sánchez, & Vosloo, ; Simulundu et al, ; Wilkinson, Pegram, Berry, Lemche, & Schels, ). A domestic cycle dependent on direct or indirect transmission amongst domestic pig populations without involvement of wild hosts or vectors occurs throughout the region.…”