Limited Exchange of Salmonella Among Domestic Pigs and Wild Boars in Italy

The study assessed Salmonella carriage in wild boars (Sus scrofa) and compared their isolates with those recovered from the domestic swine population of the same area of northern Italy (Emilia-Romagna), characterized by intensive pig farming and rather high density of wild boars. A total of 189 wild boars hunted during twelve months (2017–2018) were tested for Salmonella in mesenteric lymph nodes (MLN) and faecal samples. Antimicrobial resistance of recovered strains was tested against 14 antimicrobials. Salmonella was detected in 33/189 wild boars (17.5%), specifically from 30/189 MLN (15.9%) and 6/189 faecal samples (3.2%). Three animals were positive in both samples. Thirteen Salmonella serovars were identified, i.e. Typhimurium (the most common), Bovismorbificans, Coeln, Derby, Enteritidis, Gaminara, Hessarek, Houtenae IV, Kottbus, Napoli, Stanleyville, Thompson and Veneziana. Salmonella carriage was higher in warm than in cold months (P = 0.0013). Pregnancy status was never associated with Salmonella carriage, with significant difference in the recovery of the pathogen between non-pregnant and pregnant females (P = 0.003). Only one resistance pattern to streptomycin and tetracycline was found in 15 isolates (41.7%) belonging to Typhimurium (14/14; 100%) and Kottbus (1/3; 33.3%) serovars. Overlap with isolates from farmed pigs was limited at serotype level (Typhimurium, Derby, Enteritis, Bovismorbificans, Kottbus) and absent at PFGE level, and also antimicrobial resistance patterns were substantially different. This evidence indicates a substantial segregation of the two animal populations with regard to infectious contacts, possibly suggesting that biosecurity measures in place at industrial farm level limit the exchange of Salmonella.