Histology, prevalence, and environmental sources for pulmonary silicates depositions in domestic and wild animals

Abstract

The source and significance of pulmonary silicate crystals in animals and people are poorly understood. To estimate the prevalence and characterize the pulmonary crystalline material in animals from St. Kitts, tissue samples from dogs, horses, cattle, sheep, goats, pigs, chickens, mongooses, and monkeys were examined by light microscopy, scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDXA), and x-ray diffraction. Crystalline material was seen in 201 of 259 (77.6%) lung samples as perivascular and interstitial accumulations of heterogeneous crystalline particulate material, free or within macrophages (silicate-laden macrophages [SLMs]), mostly lacking evidence of chronic inflammation or fibrosis. The crystalline material was birefringent, basophilic on acid-fast, and composed of silicas on SEM/EDXA. Mongooses (100%) and monkeys (98%) had the highest prevalence of SLM, followed by cattle and chickens. Lesions were graded on a 3-point scale based on the histologic location and extent of silicates and SLM and were significantly more severe in mongooses (median = 3) than in monkeys (median = 2), dogs (median = 2), and chickens (median = 1). On EDXA, the crystalline material from lungs, air, and topsoil was composed of silicon, oxygen, aluminum, and iron, with a particulate matter size between 2.5 and 10 µm. We hypothesize Saharan dust, volcanic ash, topsoil, and rock quarry dust are potential sources of siliceous dust inhalation and SLM accumulations lacking chronic inflammation (silicosis); dust generation may be potentiated by road vehicle or wind suspension. Future investigations are warranted on the role of silicate inhalation and respiratory comorbidities in people, with monkeys, mongooses, or chickens serving as possible sentinels for exposure.

A cross-sectional observational study of birefringent particulates in bronchoalveolar lavage cytology in horses with equine asthma from the West v East coasts of the USA

“…It is logical that individuals who spend large amounts of time outdoors in arid regions, including children [ 23 ] and agricultural workers, have been identified as having non-fibrotic respiratory diseases caused by or exacerbated by geogenic dust [ 24 ]. Non-fibrogenic silicosis, described as silica-laden macrophages (SLM), has recently been described in various animal species on the island of St. Kitts, with higher levels of silica found in species that are likely to graze or roll in dust [ 25 ]. Similarly, a study looking at 100 autopsies in 11 mammalian species and 8 avian species living in the southwest of the US showed mild pulmonary lesions despite silicate-laden macrophages; on energy-dispersive x-ray analysis, 95% of these were silicates [ 26 ].…”