Lack of detection of Mycobacterium microti infection in wild rodents from a free-ranging wild boar outbreak area

Wild small rodents are considered the natural reservoirs of Mycobacterium microti, a member of the Mycobacterium tuberculosis complex (MTBC) that can cause tuberculosis (TB) in humans and animals, as well as interfere with current tuberculosis eradication plans in livestock. A cross-sectional study was carried out in the Catalan Pyrenees (Iberian Peninsula) in an area where M. microti was previously isolated from wild boars, to evaluate the role of micromammals in the epidemiology of this outbreak. A total of 350 wild rodents were necropsied (306 Murinae and 44 Arvicolinae) in spring and autumn during two consecutive natural years. Tissues were analyzed by histopathology to look for TB-like lesions and by qPCR and culture to detect MTBC. Sera were analyzed by MTBC-specific ELISA. No evidence of TB infection in wild rodents was confirmed. Results suggest that small rodents did not play a role in the epidemiology of M. microti in the area. The source of this mycobacterium remains unknown, but previous detections of M. microti in various species in southern France suggest the movements of wild boars across the French Pyrenees as the most likely origin of the outbreak detected in the Iberian Peninsula.