Abstract
The European wild boar (WB) (Sus scrofa) population has rapidly expanded over the years, raising public health concerns over the species reservoir of several pathogens, including Mycobacterium microti (Mm), a Mycobacterium tuberculosis complex member. In this study, we aimed to investigate the Mm natural infection in WB in Lombardy and Emilia Romagna Italian regions by statistically evaluating the granulomatous lesions' histological features and Mm microbiological isolation. We analyzed 103 WB retropharyngeal and submandibular lymph nodes (LNs) for Mm identified by gyrB PCR-restriction fragment length polymorphism, and were retrospectively selected and histologically assessed. For each sample, Hematoxylin-eosin and Ziehl–Neelsen stained slides were evaluated. Considered histological variables were: the number of granulomas, size and maturational stage of granulomas, granulomas completeness within the section, number of multinucleated giant macrophages (MGMs), and acid-fast (AF) bacilli per granuloma. Furthermore, Mm microbiological results were also considered. Mm microbiological isolation was negatively influenced by granulomas maturation and positively affected by AF bacilli's presence within the section. Granuloma maturation was positively influenced by granuloma size and granuloma incompleteness and negatively affected by the number of granulomas in the section and the number of MGMs within the granuloma. The results indicate that granuloma maturation should ensures an efficient containment of Mm infection in the WB, suggesting that the intra-species transmission of the disease might be an unlikely event.
Highlights
The European wild boar (WB) (Sus scrofa) population has rapidly expanded over the last decades [1, 2]
In this study, were histologically and statistically investigated lymph nodes (LNs) of WBs naturally infected with M. microti (Mm), a member of the Mycobacterium tuberculosis complex (MTBC) whose epidemiological dynamics in WBs are still largely unknown, probably due to its difficult identification before the advent of diagnostic molecular methods [2]
The first step was to establish the grade of the granulomas according to the scheme described by Wangoo et al [18] and to statistically investigate how the various maturational stages of the granulomas, as well as the presence of AF bacilli and multinucleated giant macrophages (MGMs) in the LN histological section, influenced the microbiological isolation of Mm
Summary
The European wild boar (WB) (Sus scrofa) population has rapidly expanded over the last decades [1, 2]. This dramatic increase has been attributed to multiple factors, including more favorable climatic conditions, a reduction in natural predators, and, in particular, a decrease in human hunting activity, which was the primary source of WB population control [3]. M. bovis, M. caprae, and M. microti (Mm) are the MTBC members identified in WB, and the role of the latter as a reservoir for these pathogens is demonstrated or highly suspected in various ecosystems [1, 6,7,8,9,10]. WB tuberculosis seems to have hindered eradicating the disease in different zootechnical–rural realities, endangering animal products’ consumption, hampering animal movement toward tuberculosis free areas, and burdening the costs associated with veterinary controls [2]
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