Despite the implementation of several eradication programmes, African swine fever (ASF), a viral disease in pigs caused by a DNA virus (ASFV), has been present in Sardinia (Italy) since 1978. Several studies have been carried out on the epidemiology of ASF in Sardinia, aimed at attaining a better understanding of the role of the risk factors related to ASFV persistence, but those studies did not address the social aspects involved. This work sought to bridge this gap, identifying the main social risk factors associated with ASF persistence. With this aim, this study takes into account not only the known "biological" risk factors identified in previous studies, but also the direct correlation between ASF persistence and well-known socio-economic aspects. The demographic characteristics, the Material Deprivation Index (IDM) and the non-compliance with the rules on ASF controls, including the traditional method of keeping free-range pigs has been evaluated. To assess the weight of each risk factor, data about pig farms, wild boar and social factors in Sardinia, were analysed using the Negative Binomial Regression Model. The main outcome was the number of domestic pig outbreaks occurring in Sardinian during 2011-2016. The effect in terms of the odds ratio (OR) was calculated to each factor included. The biological risk factors identified covered the number of animals (OR = 3.33, p < .0001, by 100 animals) and farms (OR = 1.07, p = .006, by 10 farms), the animal movements (OR = 1.64, p = .001, by 10 movements), the presence of illegal pigs (OR = 6.87, p < .0001) and the ASFV prevalence in wild boars (OR = 1.30, p = .001). Among the socio-economic factors, the compliance with control measures (OR = 0.90, p < .0001), the human population increasing by 1000 people (OR = 0.89, p < .0001), the growing age of the farmers (OR = 0.66, p = .025, by 5 years) and non-relationships with other farms (OR = 0.85, p < .001), decreased the ASF risk. The deprived condition (i.e. cultural and material deprivation, lack of resources and overcrowding index) increases the risk of about four times, as the low educational level (OR = 3.97, p = .002). Having highlighted the important role of social conditions, this risk definition allows understanding the Sardinian situation and may be useful to decision-makers to draft specific control strategies against this disease in the island, which should take into account local risk factors.

SUMMARYAfrican swine fever (ASF) is a notifiable infectious disease, caused by the ASF virus (ASFV), which is a DNA virus belonging to the family Asfarviridae, genus Asfivirus. This disease has gained importance in the last decade after its spread in several countries in Eastern and Central Europe, and more recently, in China. Despite the efforts made to eradicate it, ASF is still present on the Mediterranean island of Sardinia (Italy) and has been since 1978. ASF risk factors on the island have been analysed in previous studies; the role of free‐ranging pigs in virus persistence has been suggested, but has not been fully elucidated. The most recent eradication plan provides more stringent measures to combat free‐ranging pigs and any kind of illegality in the pig sector. From December 2017 to June 2018, a total of 29 depopulation actions were performed in 13 municipalities in central Sardinia, during which 2,281 free‐ranging pigs were culled and more than 50% of them were tested for ASFV and antibody presence (1,218 and 1,416, respectively). A total of 651 pigs were seropositive, with a mean seroprevalence of 53.4% (CI 95% = 50.6–56.3), and 38 were ASFV positive (virus prevalence = 2.6%; CI 95% = 2.1–3.0). To the best of our knowledge, the present study is the first to provide a complete evaluation of this millennial system of pig farming and ASFV prevalence in free‐ranging pigs. Furthermore, it has emphasised the necessity of combining the maintenance of an epidemiological surveillance program with continuous education of farmers and other people involved in pig husbandry, based on cultural and economic aspects.

From more than 40 years African swine fever (ASF) is endemic in Sardinia. Historically, areas at higher risk are located throughout some inland parts of this island where domestic pigs are still illegally kept in semi-wild conditions, living in contact with the local wild boar population, thereby creating perfect conditions for disease endemicity. A new eradication plan (EP-ASF15-18) has been ongoing for the past 3 years, based on a comprehensive strategy adapted to the local situation and focused on strong actions on domestic pig farms, wild boars (WB), and the third Sardinian typical involved population [illegal free-ranging pigs (FRPs)]. A fundamental aspect of the plan is the classification of pig farms as “controlled” or “certified,” based on clinical, structural, and biosecurity characteristics. The eradication plan also provides for strong action against illegal farms and pig meat marketing channels. In addition, this plan establishes specific control measures for WB hunting and ASF checks. Each control strategy is specifically based on municipality risk level, to focus actions and resources on areas at higher risk of endemic or re-emerging ASF. Thus, precise risk classification is fundamental to this goal. The aim of the present work was to establish an ASF risk index, to provide a summary measure of the risk level in the Sardinian municipalities. This synthetic measure can express the different aspects of a multidimensional phenomenon with a single numerical value, facilitating territorial and temporal comparisons. To this end, retrospective data (years 2011–2018) were used. The ASF risk index is the result of the algorithmic combination of numerical elementary indicators: disease prevalence in the suid populations, WB compliance with EP-ASF15-18, domestic pig compliance with EP-ASF15-18, and presence of FRPs. A negative binomial regression model has been applied and predictors calculated to obtain a risk index for each municipality. The result of the risk analysis was discussed and considered according to expert opinion and consensus. The results of this study, expressed as risk score and classified into five risk levels, can be used to help define actions to be carried out in each Sardinian municipality, according to the risk assessment for the territory.

African swine fever virus (ASFV), the cause of a devastating disease affecting domestic and wild pigs, has been present in Sardinia since 1978. In the framework of the regional ASF eradication plan, 4484 illegal pigs were culled between December 2017 and February 2020. The highest disease prevalence was observed in the municipality with the highest free-ranging pig density, and culling actions drastically reduced ASFV circulation among these animals. ASFV-antibody were detected in 36.7% of tested animals, which were apparently healthy, thus, the circulation of low-virulence ASFV isolates was hypothesized. ASFV genome was detected in 53 out of 2726 tested animals, and virus isolation was achieved in two distinct culling actions. Two ASFV haemadsorbing strains were isolated from antibody-positive apparently healthy pigs: 55234/18 and 103917/18. Typing analysis revealed that both isolates belong to p72 genotype I, B602L subgroup X; phylogenetic analysis based on whole genome sequencing data showed that they were closely related to Sardinian ASFV strains collected since 2010, especially 22653/Ca/2014. Our data suggested the absence of immune-escaped ASFV variants circulating among free-ranging pigs, indicating that other elements contributed to virus circulation among these animals. Understanding factors behind disease persistence in endemic settings might contribute to developing effective countermeasures against this disease.

African swine fever (ASF) severely threatens the swine industry worldwide, given its spread and the absence of an available licensed vaccine, and has caused severe economic losses. Its persistence in wild boar (WB), longer than in domestic pig farms, and the knowledge gaps in ASF epidemiology hinder ASF virus (ASFV) eradication. Even in areas where disease is effectively controlled and ASFV is no longer detected, declaring eradication is difficult as seropositive WBs may still be detected. The aim of this work was to estimate the main ASF epidemiological parameters specific for the north of Sardinia, Italy. The estimated basic (R0) and effective (Re) reproduction numbers demonstrate that the ASF epidemic is declining and under control with an R0 of 1.139 (95% confidence interval (CI) = 1.123–1.153) and Re of 0.802 (95% CI = 0.612–0.992). In the last phases of an epidemic, these estimates are crucial tools for identifying the intensity of interventions required to definitively eradicate the disease. This approach is useful to understand if and when the detection of residual seropositive WB is no longer associated with any further ASFV circulation.