Mesenteric lymph node granulomatous lesions in naturally infected wild boar (Sus scrofa) in Portugal—Histological, immunohistochemical and molecular aspects

• Mesenteric granulomatous lymphadenitis of wild boar were studied.
• Granulomatous lesions consisted mainly in stage III and stage IV granulomas.
• Immunohistochemistry was used to detect CD3 and CD79α molecules.
• Molecular genotyping and culture identified Map, M. bovis, or Map-M.bovis co-infection.
• Similar percentages of CD3 and CD79α regardless of Map, M. bovis or Map-M bovis co-infection.

Several studies have demonstrated that wildlife reservoirs of mycobacteria are responsible for the maintenance and spreading of the infection to livestock and wildlife counterparts. Recent data report the role of wild boar (Sus scrofa) as a reservoir for Mycobacterium bovis. This study was conducted to evaluate the chronic inflammatory response in the mesenteric lymph nodes (MLN) of wild boar with granulomatous lymphadenitis (n = 30). Morphological parameters of the lesions were recorded. The expression of CD3 and CD79α molecules was evaluated by immunohistochemistry. Molecular genotyping and culture to identify mycobacteria were performed. The lesions consisted mainly of stage III and stage IV granulomas. CD3 and CD79α positive cells were observed in 15 (50%) and in 11 (36.6%) MLN, respectively. In these lesions, higher percentages of T lymphocytes were found and a limited number of animals exhibited a tendency for an increased percentage of B lymphocytes. Our results suggest that there are similar percentages and distribution patterns of CD3 and CD79α in the lesions, regardless of the presence of Mycobacterium avium subsp. paratuberculosis (Map), M. bovis or Map-M. bovis co-infection, and confirm that wild boar is both susceptible and could be an important Map and M. bovis wild reservoir in the study area.