Epidemiological Significance of the Domestic Black Pig (Sus scrofa) in Maintenance of Bovine Tuberculosis in Sicily

Abstract

Bovine tuberculosis (bTB) is an emerging disease among wild animals in many parts of the world. Wildlife reservoir hosts may thus represent a potential source of infection for livestock and humans. We investigated the role played by the Sicilian black pig, an autochthonous free- or semi-free-ranging domestic pig breed, as a potential source of bTB infection in an area where bTB prevalence in cattle is high. We initially performed a preliminary field study to assess the occurrence of bTB in such animals. We sampled 119 pigs at abattoir and found 6.7% and 3.4% of them to be affected by gross tuberculous-like lesions (TBL) and Mycobacterium bovis culture positive, respectively. We then proceeded to investigate the dissemination and characteristics of lesions in a second field study performed on 100 animals sampled from infected herds. Here, tissues collected at the abattoir were examined macroscopically, microscopically, and by culture tests. Most pigs with TBL showed generalized lesions in both gross and histological examinations (53% and 65.5%, respectively). Head lymph nodes were the most frequently affected in both localized and generalized TB cases observed macroscopically and microscopically. M. bovis was the most frequently isolated etiologic agent. The molecular characterization of isolates from both field studies by spoligotyping and analysis of 12 mycobacterial interspersed repetitive-unit-variable number tandem repeat (MIRU-VNTR) loci, followed by their comparison to isolates of cattle origin, suggested a potential transmission of mycobacteria from domestic animals to black pigs and vice versa. Our findings, along with ethological, ecological, and management considerations, suggest that the black pig might act as a bTB reservoir in the ecosystem under study. However, additional studies will be necessary to establish the true epidemiological significance of the Sicilian black pig.

Interactions between four species in a complex wildlife: livestock disease community: implications for Mycobacterium bovis maintenance and transmission

“…However, pigs also showed moderate levels of home range overlap with cattle and the highest rate of boundary crossings. Pigs may be an important part of the disease cycle in this region, as has been previously identified in another Mediterranean system in Sicily (Di Marco et al 2012). Further research and testing of pig and red deer movements and disease in this area may be important for a fuller understanding of disease maintenance and spread.…”

“…At present, pigs are not monitored for TB in Europe, though M. bovis infection is increasingly reported in pigs in several countries (e.g. Di Marco et al 2012;Bailey et al 2013). In south-central Spain, pigs are increasingly being refused by slaughterhouses due to visible TB-compatible lesions (Gomez-Laguna et al 2010).…”

Detection and Molecular Characterization of Mycobacterium microti Isolates in Wild Boar from Northern Italy

“…At present, the wild boar is considered a reservoir for tuberculosis in Iberia (29,35), whereas in Italy, it is considered a spillover host (27,36). Recently, a study conducted in Sicily of free-ranging domestic black pigs suggested a role in the maintenance of bTB in this ecosystem (37).…”

Introduction to this issue: Dealing with TB in wildlife

“…Moreover, some non-bovine domestic and semi-domestic hosts, particularly pigs, goats, camelids or elephants, deserve much more attention regarding their growing role in infection maintenance (e.g. [3,6,7]). …”