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.