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).