Prévalence des cas de lymphadénite granulomateuse sous‐maxillaire chez des porcs abattus en Belgique

In pigs the Mycobacterium avium complex (MAC) causes granulomatous lymphadenitis. Carcasses with such lesions must be detected, as parts of the affected carcasses and organs have to be condemned. These nontuberculous mycobacteria are opportunistic pathogens which have acquired an increasing importance in public health in recent decades due to their ability to cause lung diseases, lymphadenitis in children and systemic infections in immunocompromised patients ‐ even if the potential risk of infection of an immunocompromised person by MAC in the consumption of undercooked pork still has to be determined. The first objective of this study was to evaluate the prevalence of submandibular granulomatous lymphadenitis in pigs slaughtered in Belgium. Between August 2010 and September 2011, 16,211 carcasses were inspected by the same veterinarian in 2 slaughterhouses – one in Flanders, the other in Wallonia. Eighty‐six suspected cases of submandibular granulomatous lymphadenitis (0.53% of pigs; 95% Confidence Interval: 0.42‐0.65%) were identified, collected and submitted to histopathological (Ziehl‐Neelsen and haematoxylin‐eosin staining) and bacteriological (culture, PCR, molecular typing) tests. The second objective of the study was to characterize lesions and to identify the relative importance of MAC and Rhodococcus equi to explain the lesions. Mycobacterium avium subsp. hominissuis (MAH) was isolated from 6 lymph nodes (7.0%; 95% CI: 2.6‐14.6%) and Rhodococcus equi from 45 (52.3%; 95% CI: 41.3‐63.2%). The final objective of the study consisted in farm investigation to evaluate the possible source of contamination of pigs by MAH. Potential sources such as sawdust, water, wild birds and/or cattle were identified.