Epidemiological surveillance of Mycobacterium tuberculosis complex in extensively raised pigs in the south of Spain

Abstract

The role of domestic pigs in the epidemiology of Mycobacterium tuberculosis complex (MTC) is considered to be limited due to the characteristics of intensive production systems. However, in southwestern Spain, Iberian pigs are usually raised under extensive management systems, sharing their habitat with other domestic and wild species, some of which may act as reservoirs of MTC. Our objective was to determine the seroprevalence, risk factors, spatial distribution and spoligotypes of MTC circulating in extensively farmed pigs in Andalusia (southern Spain), a region with a high prevalence of tuberculosis in both cattle and wild boar populations. Serum samples from 3622 extensively-raised Iberian pigs from 129 randomly selected farms were tested for antibodies against MTC using an indirect (P22) ELISA. Antibodies to MTC were detected in 82 pigs (2.3%; 95%CI: 1.8–2.8%). Seropositivity was significantly higher in sows (3.7%) than in fattening pigs (1.7%) (P = 0.0001). Herd prevalence was 24.8% (95%CI: 17.4–32.3%). Two risk factors were associated with MTC seropositivity on farms: herd size (higher seroprevalence on larger farms) (OR=1.001; 95%CI: 1.000–1.002), and the presence of neighboring goat flocks (OR = 7.345; 95%CI: 1.464–36.848). Two statistically significant spatial clusters (P < 0.001) were identified in the north-west of Andalusia. A total of 25 different MTC spoligotypes were isolated in pigs bred extensively in the study area. Based on the serological and molecular results obtained in the current study, it is possible that extensively raised Iberian pigs may act as an MTC reservoir in Mediterranean ecosystems. The high herd prevalence, as well as the identification of significant spatial clusters, indicates widespread, but not homogenous MTC circulation among extensively-managed pig farms. Risk-based surveillance and control programs should be implemented on this type of farms in Spain.