Silica-laden macrophages (SLMs), bronchial lymph node, badger.

<p>Focally-extensive aggregation of SLMs in the absence of collagen deposition. (A) SLMs are strongly birefringent under polarizing light. Massons trichrome stain. x100. (B) No evidence of associated collagen deposition on Massons trichrome stain (stains collagen blue). x100.</p

Distribution of silica-laden macrophage (SLM) scores in lymph nodes and lung tissue of <i>M</i>. <i>bovis</i> positive and negative badgers.

<p>Distribution of silica-laden macrophage (SLM) scores in lymph nodes and lung tissue of <i>M</i>. <i>bovis</i> positive and negative badgers.</p

Bar chart comparing cumulative silica-laden macrophage (SLM) scores in tissues from badgers with positive and negative <i>M</i>. <i>bovis</i> infection status.

<p>Bars represent the cumulative SLM score per tissue across groups of <i>M</i>. <i>bovis</i> positive (n = 30) and <i>M</i>. <i>bovis</i> negative (n = 30) individuals.</p

Validation of badger lymph node scoring categories.

<p>Boxplots represent the total number of silica-laden macrophage (SLM)-positive fields of lymph nodes within each scoring category 1–3 (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0190230#pone.0190230.g001" target="_blank">Fig 1</a>). 10 slides were examined per category, and 1000 fields assessed per slide. A positive field was defined as one that contained at least one SLM. One outlier has been omitted from this graph (Scoring category 3: 867).</p

Grouped bar graph illustrating the proportion (in %) of badgers in each scoring category (x-axis) among age classes.

<p>Given are examples of score distribution among age classes (young (n = 10); adult (n = 31); old (n = 19)) for an intrathoracic (A) and extrathoracic (B) lymph node (LN). (A) Left tracheobronchial LN; (B) Left popliteal LN. Differences in distribution between age classes were statistically significant (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0190230#pone.0190230.t003" target="_blank">Table 3</a>).</p

Environmental dust inhalation in the European badger (<i>Meles meles</i>): Systemic distribution of silica-laden macrophages, pathological changes, and association with <i>Mycobacterium bovis</i> infection status

<div><p>Chronic inhalation of crystalline silica and silicates may lead to severe lung disease in humans, termed silicosis. The disease is an occupational health concern in miners and related professions worldwide. Silicosis is also a strong risk factor for tuberculosis in humans. Due to its subterranean lifestyle, the European badger (<i>Meles meles</i>) is continuously exposed to environmental dust, while this species is also susceptible to tuberculosis, caused by <i>Mycobacterium bovis</i>. To date, a thorough investigation of mineral dust retention and its possible implication as a risk factor for mycobacterial infection in badgers has not been performed. The aims of this retrospective histological study were (1) to describe the systemic tissue distribution of silica-laden macrophages (SLMs) in badgers; (2) to compare the amount of SLMs in tissues of badgers of differing <i>M</i>. <i>bovis</i> infection status, pulmonary SLM burden and age; and (3) to assess whether inflammation was associated with SLMs. We assessed lung, lymph nodes, liver and spleen of 60 wild-caught badgers of known <i>M</i>. <i>bovis</i> infection status for the presence of SLMs using polarizing light microscopy. SLMs were consistently present within the lungs and were widely distributed throughout the lymphatic system. No inflammatory reaction to SLMs, as occurs in human silicosis, was observed in any tissue. Distribution and amount of SLMs were similar between <i>M</i>. <i>bovis</i> positive and negative badgers, and we were not able to show an association between the amount of SLMs and <i>M</i>. <i>bovis</i> infection status. The amount of SLMs within intra- and extrathoracic lymph nodes was positively associated with the amount of pulmonary SLMs, and with age. This is the first report of substantial and systemic tissue retention of mineral dust particles in a mammalian species lacking associated chronic inflammation (i.e. silicosis). We further highlight different pathogenetic mechanisms underlying silicosis and benign SLM accumulations following siliceous dust inhalation.</p></div

Distribution and cumulative silica-laden macrophage (SLM) score across badger lymph nodes, tonsils, liver and spleen.

<p>Bars represent the cumulative SLM score per tissue across the study population of 60 badgers.</p

Distribution of silica-laden macrophage (SLM) scores in lymph nodes of badgers with a high and low lung SLM score, respectively.

<p>Distribution of silica-laden macrophage (SLM) scores in lymph nodes of badgers with a high and low lung SLM score, respectively.</p

Silica-laden macrophages (SLMs), lung, badger.

<p>Multifocal interstitial accumulations of macrophages engorged with crystalline material. (A) Crystalline material has a light brown color and finely granular to spicular appearance in routinely stained sections. H&E. x200. (B) Crystalline material is strongly birefringent under polarizing light, consistent with silica and silicates. H&E, x200. (C) No evidence of associated collagen deposition on Massons trichrome stain (stains collagen blue). x200.</p

Percentages and number of cases over the total sample size for each neutering status group; intact and neutered early or late for female Golden Retrievers (1–8 years old) diagnosed with hip dysplasia (HD), cranial cruciate ligament tear (CCL), lymphosarcoma (LSA), hemangiosarcoma (HSA), and/or mast cell tumor (MCT) at the Veterinary Medical Teaching Hospital of the University of California, Davis, from 2000–2009.

<p>For CCL the difference between intact and early-neutered was statistically significant (K-M). For HSA, the differences between early and late-neutered and intact and late-neutered groups were statistically significant (RR), as were differences for MCT between early and late-neutered groups. A similar statistical comparison for late neutering and intact groups was not possible for MCT because there were 0 cases in the intact group.</p