2.1. Study area
Ardèche is a territory of South-Eastern France (Fig. covering an area of 5.500 Km2 with an altitude A) ranging between 140 and 1750 m asl and crossed by a large network of rivers and streams forest vegetation (52%) of exceptional diversity combining oak, acorn, chestnut, wild pine and red beech forests (see Fig. 2). Its climate is predominantly Mediterranean (0-28 °C) and annual rainfall ranges between 30 and 2000 mm. The region is representative of a rural Southern French environment with a strong cultural heritage where traditions are preserved, including ancestral outdoor pig farming under fruit forest trees such as oak or chestnut and wild boar hunting. In addition, a large area of abandoned chestnut trees benefits pig farmers. Animals can therefore eat chestnuts throughout the fall season, at no cost to the farmer. Likewise, forest cover provides ideal conditions for the establishment of wild boar, which feeds in abundance on acorns, chestnuts and beechnuts (Baubet, Vassant, Brandt, & Maillard, 2008; Schley & Roper, 2003).
In Ardèche and many other rural areas in France, intensive pig farming started to develop a few decades ago, during the industrialization of pig production. Competition between regions on this intensive system based on production costs and technical performance led to a simplified map of pork production in France, with a high concentration of industrial intensive pig farms in the West of the country and the limited development of smaller scale pig production in other regions such as the study area, where outdoor systems and farm processing have been developing progressively during the last decades (Dourmad, Salaün, Lebret, & Riquet, 2018).
Based on the detected cases of wild boar carcasses presenting lesions, clinical signs and bacteriological or genetic evidence of OD between 2013 and 2016 (Perrat et al., 2022), a polygon of 1981 Km2 was spatially identified and designed throughout the manuscript, as OD area (Fig. 1B and C, Fig.3 and Fig.4).