Macroscopic and Histological Examination
Of the lymph nodes from the 101 wild boars showing growth ofMycobacterium spp., 25.7% showed macroscopic pathological lesions (Table 2). Macroscopic visible lesions such as single or multiple caseous, necrotic and calcified nodules of different sizes (1-30 mm) were observed (n=14). In addition to the described nodular lesions, lymph node enlargement, discoloration and induration were recorded (n = 26). Histologically, in 70% of the samples presenting nodular lesions, a moderate granulomatous lymphadenitis with scarce giant cells of Langhans type surrounding or adjacent of a mild to moderate focal-extensive necrosis was visible. The lymph nodes showed additionally a moderate to severe reactive hyperplasia and a mild to moderate eosinophilic lymphadenitis. Mah , the predominant species identified in the present study, was found in lymph nodes with and without macroscopic changes. On the contrary, M. microti (n=5) and M. florentinum (n=3) infections were always associated with visible lesions such as caseous, necrotic and calcified nodules. A subset of lymph nodes (n = 14) presenting macroscopic lesions compatible with mycobacterial infections were examined histologically. Lymph nodes of animals infected by M. microti and M. florentinumshowed all granulomatous lymphadenitis characterized by focal-extensive necrosis and mild inflammatory infiltration of epithelioid macrophages, neutrophils, multinucleated Langhans giant cells and eosinophils (Fig. 3A and 3C). In three cases dystrophic calcifications were markedly present. Overall, the lesions observed macroscopically and histologically were circumscribed and of mild to moderate entity. Ziehl-Neelsen staining revealed scanty AFBs according to the IUATLD and WHO grading scales. Samples that presented visible lesions compatible with tuberculosis and tested positive for M. microti showed ”croissant-like” or S-shaped AFBs, which is commonly associated with this species (van Soolingen et al., 1998). Acid-fast bacilli were observed extracellular and within macrophages (Fig. 3B).