Introduction
Wild boar (Sus scrofa ) populations have been growing in high numbers for several decades both in Europe and in other countries of the northern hemisphere generating serious ecological, economic and sanitary costs (Ward, 1963). At the same time, the number of outdoor pig farms is increasing because of consumers’ demand for higher quality products issued from animal friendly production practices (Åkerfeldt, Gunnarsson, Bernes, & Blanco-Penedo, 2021). These two parallel developments facilitate an increasing occurrence of interactions between domestic pigs and wild boars, which can have several sanitary and environmental consequences. This phenomenon is widespread in most of the distribution area of Sus scrofa in Eurasia and this topic is raising increased international attention with the global spread of African swine fever in Europe and Asia, which can facilitate the circulation of this virus and other pathogens at the wildlife-livestock interface (Boklund et al., 2020; Jori, Payne, Stahl, Nava, & Rossi, 2018; Triguero-Ocaña et al., 2021). Several studies found in the literature have assessed the frequency and intensity of wild boar/domestic pig interactions from the ecological or behavioral perspective in the USA (Wyckoff, Henke, Campbell, Hewitt, & VerCauteren, 2009) and Europe (Wu et al., 2012). A recent study in Corsica characterized major types of direct and indirect contact, including sexual interactions (between male wild boars and domestic sows), agonistic (between wild and domestic boars) and indirect trophic interactions (Jori et al., 2017).
However, other sources of contacts between wild and domestic pigs such as the interaction of wild boar populations with abandoned pot-bellied pigs becoming feral have been more rarely explored in the available literature. This phenomenon is growing in developed countries purchasing pot-bellied pigs as pets but has been only reported in scientific literature very occasionally to date. (Delibes–Mateos & Delibes, 2013; Soler, Casas, Closa-Sebastià, Sanz, & Martorell, 2021).
In any case, belonging to the same species, wild boars and domestic pigs can share a large diversity of pathogens through a diversity of pathways (Jori et al., 2018; Miller et al., 2017). Some of them, such as Aujeszky disease (Boadella, Gortázar, Vicente, & Ruiz-Fons, 2012; Meier, Ruiz-Fons, & Ryser-Degiorgis, 2015) or porcine brucellosis with Brucella suis Biovar 2, have been often been controlled or eradicated in intensive domestic pig production systems, but are more difficult to control in outdoor production systems and remain prevalent in free ranging wild boar populations (Wu et al., 2012). Similarly, wild boars can also be affected by pathogens common in domestic pig farms such as hepatitis E (Charrier et al., 2018; Jori et al., 2016), porcine mycoplasmosis (Goedbloed et al., 2015) or porcine respiratory-syncytial syndrome (J. Wu et al., 2011) and become exposed to antimicrobial resistance and other environmental contaminants (Torres et al., 2020). In recent years, several fatal outbreaks have been reported in wild boars from Southern France, caused by a strain enterotoxemicEscherichia coli (serotype O139K82), with virulence markers and symptoms characteristic of oedema disease (OD) in domestic pigs (Decors et al., 2015; Petit et al., 2020). Those episodes of wild boar mortality in the Southern French region of Ardèche were first reported in 2013 (110 detected cases) and decreased progressively during the following years with 51 cases in 2014, 26 cases in 2015 and only 6 cases in 2016 (Decors et al., 2015). These emerging events in wild boar populations highlight the need to explore the factors associated with those outbreaks, including the potential importance of direct or indirect interactions between wild boars and domestic pigs. These types of contacts are reported when outdoor pig farming overlaps with wild boar or feral pig presence in several regions in Eurasia and the Americas (Jori et al., 2018; N. Wu et al., 2011; Wyckoff et al., 2009). Corsica is possibly one of the areas in France where these types of interactions have been often reported due to the widespread of traditional extensive farming systems in the Island (Charrier et al., 2018; Gisclard, Charrier, Trabucco, & Casabianca, 2021; Jori et al., 2017). Conversely, interactions between wild boars and domestic pigs are suspected to be less common in continental France, but no studies have explored the current importance of this phenomenon to date.
Therefore, the goal of our study was i) to report on the predominant pig farming patterns the continental French region of Ardèche, ii) to examine the potential importance of domestic pig-wild boar interactions in this rural context and iii) to explore the potential association with previous mortality outbreaks attributed to OD among the local wild boar populations.