According to the World Organization for Animal Health (OIE), African swine fever virus (ASF) is the most important disease-causing pathogen affecting the domestic swine population globally1. The high mortality induced in naïve pig populations is devastating to pig farmers, especially given that there is no chemotherapy or vaccine currently available for disease control. Prevention of the disease relies on strict biosecurity measures which are frequently not effectively applied, particularly in the endemic areas. As a result, the virus and associated disease have spread into many new areas that have not previously been reported (reviewed by2,3,4). Historically, the disease was first described in East Africa in the 1920s5. The first occurrence outside Africa, of a virus classified in p72 genotype I, was reported in 1958 and again in 1961 from Lisbon Portugal, with subsequent spread to other regions of Europe and Latin America (reviewed by6,7). In 2007, an ASF virus (ASFV) within p72 genotype II8 was again exported through a human agency outside sub-Saharan Africa into Georgia. However, the precise geographical origin has not been identified, since genotype II is present in Mozambique, Madagascar, Malawi, Zambia, Zimbabwe and Southern Tanzania8,9,10,11,12,13,14,15,16 as represented in Fig. 1.
A map showing the geographical distribution of the two genotypes that have escaped outside Africa into other continents. While genotype I has dominated the western, genotype II is more prevalent in the eastern part of Africa. This map was constructed using QGIS software version 2.18.14 freely downloaded from https://qgis.org/en/site/.
Using a risk assessment methodology, shipment of a pork product originating from southeastern Africa, or Madagascar was highlighted as a likely source of viruses that could be disseminated into other continents17.
Between mid-2007 to date, ASF genotype II viruses, derived from the Georgia introduction, have been reported throughout the Caucasus, Russia, the Baltic republics, Czech Republic, Romania, Hungary, Bulgaria, Poland, Belgium, and most recently China18 and South-east Asia. Despite significant efforts by FAO and others to control its spread, numbers of ASFV infected animals are increasing rapidly in domestic pigs and wild boar populations, with movements of the latter facilitating the rapid geographical spread of the virus (reviewed in2).
Constituting the sole member of the genus Asfivirus within the family Asfiviridae, ASFV is the only known DNA virus causing hemorrhagic fever transmitted by an arthropod, namely Argasid soft ticks in the genus Ornithodoros. The genome of the virus is composed of a linear double-stranded DNA molecule between 175 and 195 kbp in length and containing up to 190 open reading frames depending on the virus isolate19. Multiple approaches have been used to characterize the virus20, with genotyping of the virus by full length or partial sequencing of the genes encoding the p72, p54, p30 proteins and the Central variable region now widely applied.
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