African swine fever (ASF) is a contagious and often fatal viral disease of domestic pigs and wild boar [
22] that is currently endemic in many sub-Saharan African countries, the Russian Federation, Transcaucasia, some East European countries, and Sardinia [
1]. A recent ASF outbreak was also reported in China [
8]. There is still neither a licensed vaccine nor a treatment available, and disease-control measures rely on stamping out and movement restrictions, resulting in extreme losses for producers [
22]. In Sardinia, the disease first occurred in 1978, and despite many eradication programmes it is still endemic [
3,
5,
18]. So far, all Sardinian ASFV isolates have been found to belong to p72 (B464L) genotype I, whereas genotype II ASFV isolates are circulating in the other European countries, Transcaucasia, Russia, and China, [
1,
8]. The epizootic cycle of ASFV in Sardinia is characterized by the absence of Ornithodoros ticks [
18], which are biological vectors for ASFV and have been implicated in the long-term maintenance of the virus in Spain and Portugal (
O. erraticus) and East and South Africa (
O. moubata) [
1]. There is instead evidence of endemically infected wild boar populations [
5,
16,
18]. The role of wild boars in ASFV epidemiology in Sardinia remains controversial, but several authors agree on their secondary role in ASF transmission and instead emphasize the importance of the interaction between free-ranging pigs and wild boars for the persistence of the disease [
13,
18]. Previous studies have shown that ASFV in wild boars in Sardinia tends to be self-limiting in the absence of contacts with free-ranging pig populations [
14,
20].
Molecular characterization of Sardinian ASFV strains isolated from domestic and wild pigs showed high genetic similarity. Indeed, an analysis of the genes coding for p72 and p54 proteins showed that all Sardinian strains can be classified within genotypes I and Ia, respectively [
9,
23]. Differences were instead observed in the B602L gene, which is involved in viral morphogenesis [
4], allowing the differentiation of Sardinian isolates in two temporally related subgroups (X and III). Almost all of the strains isolated from 1990 onwards (subgroup X) showed the deletion of 12-13 tetramers [
9] with respect to those isolated before 1990 (subgroup III). Likewise, [
23] reported an identical temporal subdivision of Sardinian viruses into two subgroups differing from the deletion of a six-amino-acid repeat at the C-terminus of the CD2v protein encoded by the EP402R gene, which is characteristic of the strains isolated after 1990. Ultimately, almost all of the Sardinian ASF viruses isolated after 1990 (modern strains) showed deletions in both the B602L and EP402R genes if compared to viruses isolated before 1990 (historical strains). The modern strains may have acquired some selective advantage, as suggested by their rapid and almost complete displacement of the historical strains.