Mycobacterial Infections in Wild Boars (Sus scrofa) from Southern
Switzerland: Diagnostic Improvements, Epidemiological Situation and
Zoonotic Potential
Abstract
The occurrence of mycobacterial infections in different hosts and their
implication as obligate or opportunistic pathogens remain mainly
unclear. In addition to the well-known pathogenic members of the
Mycobacterium tuberculosis - complex (MTBC), over 180 nontuberculous
mycobacteria (NTM) species have been described. Although the large
majority of the NTM are assumed to be non-pathogenic to most
individuals, an increasing trend in NTM infections has been observed
over the last decades. The reasons of such augmentation are probably
more than one: improved laboratory diagnostics, an increasing number of
immunocompromised patients and individuals with lung damage are some of
the possible aspects. Mandibular lymph nodes of 176 hunted wild boars
from the pre-Alpine region of Canton Ticino, Switzerland, were
collected. Following gross inspection, each lymph node was subjected to
culture and to an IS6110 based real-time PCR specific for MTBC members.
Histology was performed of a selection of lymph nodes presenting gross
visible lesions. Moreover, accuracy of matrix-assisted laser desorption
ionization–time of flight (MALDI-TOF) mass spectrometry species
identification was compared with sequence analysis of a combination of
housekeeping genes. Mycobacteria of the MTBC were detected in five out
of 176 wild boars (2.8%; CI95% 1.2 - 6.5) and were all confirmed to be
Mycobacterium microti by molecular methods. In addition, based on the
examined lymph nodes, NTM were detected in 57.4% (CI95% 50.0 – 64.5)
of the wild boars originating from the study area. The 111 isolates
belonged to 24 known species and three potentially undescribed
Mycobacterium species. M. avium subsp. hominissuis thereby predominated
(22.5%) and was found in lymph nodes with and without macroscopic
changes. Overall, the present findings show that, with the exception of
undescribed Mycobacterium species where identification was not possible
(3.6%; 4/111), MALDI-TOF had a high concordance rate (90.1%; 100/111
isolates) to the sequence based reference method.