Pulmonary silicosis in 2 rock hyraxes, and literature review

Abstract

Two rock hyraxes ( Procavia capensis), from the Chattanooga Zoo, were submitted separately for autopsy at the University of Tennessee Veterinary Medical Center. The first was a 4-y-old intact female that died without premonitory signs and the second was a 10-y-old intact male that was euthanized because of severe renal disease. Microscopically, the lungs of both hyraxes had multifocal-to-coalescing, <1-mm diameter aggregates of epithelioid macrophages separated by streams of fibrous tissue. Macrophages contained intracytoplasmic, clear, acicular, birefringent crystals. Transmission electron microscopy and energy-dispersive x-ray spectroscopy findings on the lung samples were consistent with silica crystal deposition. The hyraxes had been housed together on commercially sourced play sand composed of 99–99.5% quartz, a crystalline silica polymorph. The microscopic findings, transmission electron microscopy, and energy-dispersive x-ray spectroscopy of the intrahistiocytic crystals, in addition to the history of exposure to crystalline silica, were consistent with pulmonary silicosis. Pulmonary silicosis has not been reported previously in rock hyraxes, to our knowledge.

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

“…Sustained workplace exposures to silica and silicate dusts are associated with the fibrotic pneumoconioses such as asbestosis, silicosis, and coal worker’s lung in humans [ 17 ]; reported multifocal-to coalescing fibrotic pulmonary disease along with a high macrophage burden of silica in hyraxes housed on silica play sand likely falls into this category [ 18 ]. Similarly, several reports of cases of naturally occurring severe, fibrotic pulmonary silicosis more similar to pneumoconioses in humans have been reported in horses in the Monterey-Carmel Peninsula in California presumably resulting from chronic inhalation of the high levels of endemic silica (cristobolite form) [ 19 , 20 ].…”

Silica and barium: Comparison of microscopic appearance and characterization of effects of silica on cytomorphology

“…Detailed data on the purification of the barium used in the E‐Z‐EM formulation were not available, so it is unknown whether the barium compound used in this study also contained calcium. GMS identifies fungal and algal organisms but has been reported to stain silica particles 12 . Prussian blue stains for iron, including ferruginous bodies, that are often composed of silicates and silica covered with a coating of iron and protein 13 .…”

“…GMS identifies fungal and algal organisms but has been reported to stain silica particles. 12 Prussian blue stains for iron, including ferruginous bodies, that are often composed of silicates and silica covered with a coating of iron and protein. 13 We suspect that the negative results of all special stains tested for differentiating silica and barium were due to differences in the specific formulations used in our study compared to those in other reports.…”