Mycobacteriosis outbreak caused by Mycobacterium avium subsp. avium detected through meat inspection in five porcine fattening farms.

Context Between December 2010 and January 2011, 20 cases of mycobacteriosis, consisting of grossly nodular granulomatous and caseous lesions in pig carcases from five different fattening farms, were submitted to the Slaughterhouse Support Service in Barcelona, Spain. Lesions involved lymph nodes, lungs, liver and spleen. Main conclusion A mycobacteriosis outbreak caused by Mycobacterium avium subspecies avium was detected in the five pig farms. Approach Gross pathology, histopathology and bacteriological isolation followed by molecular identification of culture isolates and epidemiological investigation. Results Histopathological examination showed multifocal to coalescent, granulomatous and necrotising lymphadenitis, pneumonia, hepatitis and splenitis. Acid-fast bacilli compatible with mycobacteria were detected in some of the samples. The presence of acid-fast bacilli in some cases revealed mycobacteriosis. Bacteriological culture was performed to confirm diagnoses and identify the aetiological agent (to rule out potential involvement of Mycobacterium tuberculosis complex mycobacteria, which includes those that cause human and animal tuberculosis). PCR from culture isolates confirmed the growth of M avium complex. Further sequencing analysis determined it was M avium subspecies avium. Interpretation The most likely source of the outbreak was considered to be the feed that was shared by the five farms, which might have been contaminated with M avium subspecies avium. The fact that most of the animals presented with a clear involvement of abdominal viscera is consistent with an oral route of infection. Significance of findings The establishment of a meat inspection support network allowed for rapid management of sample submission, diagnosis and subsequent molecular identification of the mycobacteriosis outbreak, leading to an understanding of the associated risks to public health. [ABSTRACT FROM AUTHOR]