Diagnosis of Mycobacterium avium complex in granulomatous lymphadenitis in slaughtered domestic pigs

The aim of this study was to compare two diagnostic methods for the detection of Mycobacterium avium complex (MAC) infection in lymph nodes with granulomatous lymphadenitis from slaughtered domestic pigs. Fifty affected lymph nodes were collected from 50 pigs and examined microscopically and by polymerase chain reaction (PCR). Microscopically, granulomatous lesions were observed in 92% of the samples, consisting mostly of central necrosis (78%) with dystrophic calcification (46%) and associated with inflammatory infiltration by epithelioid giant cells, lymphocytes, neutrophils (92%), eosinophils (60%) and Langhans-type cells (70%). In 64% of the lesions, a capsule of connective tissue was found. Acid-fast bacilli were observed in all cases. PCR detected DNA from Mycobacterium spp. in 82% (41/50) of the lymph nodes. MAC was confirmed in 58% (24/41) and M. avium avium/silvaticum subspecies in 39% (16/41). The results of this study suggest that combined histopathology and PCR of lymph nodes are useful in the diagnosis of granulomatous lymphadenitis in slaughtered pigs