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Mesothelioma is a tumor of the serosal membranes described both in human and veterinary medicine. While in humans the relationship between mesothelioma and exposure to asbestos and some other asbestiform minerals is well known, in animals it is still difficult to establish. In this paper a case of malignant peritoneal mesothelioma probably related to asbestos exposure in a wild boar is described. At post-mortem evaluation the peritoneum, diaphragm and serosal surface of liver and kidneys showed isolated to coalescent multiple nodular lesions. Samples from diaphragm, liver and lung were collected to perform microbiological and histological investigations. To assess the presence of asbestos and/or other asbestiform minerals, SEM-EDS investigations were performed on organs and soil samples collected from the area where the wild boar lived. Microbiological investigations were negative for Mycobacterium species. Gross and histological examination were compatible with a biphasic mesothelioma, with nodules composed of epithelioid and sarcomatoid elements with high pleomorphism. Immunohistochemistry revealed only multifocal scattered positivity for WT-1 and D2-40. Asbestos fibres were detected in all samples (organs and soil) by SEM-EDS, demonstrating a potential relationship between the neoplasia and the exposure to naturally occurring asbestos (NOA). In conclusion, the results of the present study are further confirmation that wild animals, such as the boar, are suitable sentinels to indicate the risk of environmental exposure to asbestos for human populations.

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Asbestosis is a chronic lung disease caused by inhalation of asbestos, a fibrous mineral. It is one of the most severe diseases resulting from environmental contamination. We found asbestosis in a female Japanese macaque over 25 years of age that died from senility. Clear needle-like crystals were deposited throughout the lung lobes, particularly in the perivascular areas. Asbestos bodies were observed in some of these crystals. Fibrosis without inflammation was observed in the periarterial and peribronchiolar regions. The crystals were identified as tremolite, and a total of 16,633,968 asbestos bodies and 465,334,411 tremolite fibers were observed in 1 g of dry lung tissue. No tumors or pleural adhesions were seen. This is the first report of spontaneous asbestosis in a nonhuman animal.

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This analysis reviews the available literature on interspecies comparisons of the toxicity of asbestos and synthetic vitreous fibers (SVFs). This topic is of substantial practical importance because most quantitative risk analyses on the effects of inhalation of SVFs are based upon extrapolation of data from rodent inhalation studies. Available information on interspecies comparisons for both dosimetry (the relation between exposure concentration and fiber lung burden) and potency (the relation between lung burden and disease) is summarized. Dosimetry models indicate that, on a normalized basis, fiber deposition and clearance rates are lower in humans than rats. Potency is less well understood than dosimetry, in part because the source of relevant human data is asbestos studies, which are adequate to demonstrate hazard, but are problematic in other regards. There are significant interspecies differences between the mouse, hamster, rat, and human. The available evidence suggests that the rat is preferable as a model for the human. Rats develop fibrosis at comparable lung burdens [10(6) long (> 20 microm length) fibers per gram of dry lung] to those in humans. This analysis concludes that, on a weight-of-evidence basis, there is no reason to conclude that humans are more sensitive to fibers than rats with respect to the development of lung cancer.

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Discussion of the major milestones in the history of the modern uses of asbestos and the first knowledge of the health effects associated with such usage. Highlights of the studies associating exposure to asbestos with non-malignant lung diseases, lung cancer, and mesothelioma are discussed.

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Experimental inhalation in a number of studies has demonstrated that chrysotile asbestos can cause pulmonary fibrosis and both benign and malignant pulmonary tumours, two lesions which are associated in that the studies reporting high tumour rates also found high levels of asbestosis. One comparison reported that animals with malignant tumours had approximately twice the amount of fibrosis in the lung parenchyma as those of similar age without tumours. Many studies have examined the pathogenicity of asbestos administered by ingestion and most of these included chrysotile asbestos: the results have been universally negative apart from one study with amosite that contained no control animals and is best discarded. Only one inhalation study has reported an examination of the larynxes of animals: this found no pathological changes. In many studies, tumours other than the lung had been listed, but significant numbers of kidney tumours have never been recorded. Injection studies inducing mesothelioma have indicated that fibre geometry is important with long thin fibres (> 8 microns in length and < 0.25 microns in diameter) being the most carcinogenic. This has been difficult to confirm for inhaled fibres although fibres less than 5 microns in length appear to cause neither fibrosis nor pulmonary tumours. Similar results have been found with amosite for fibres up to 10-15 microns although longer fibres do produce these conditions. It is suggested that to produce pulmonary fibrosis and neoplasia fibres may need to be longer than 20 microns. Chrysotile has been shown in many studies to be removed from lung tissue much more rapidly than amphibole fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

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