Asbestosis in experimental animals

Our plain-English summary of Asbestosis in experimental animals, by J.C. Wagner (British Journal of Industrial Medicine, 1963).

The study

• Author: J.C. Wagner
• Journal: British Journal of Industrial Medicine
• Published: 1963;20(1):1-12
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001576).

Abstract

Previous animal experiments with asbestos dusts have been almost entirely confined to chrysotile asbestos. It was, therefore, decided to investigate the effects of mill dusts from the three types of asbestos that are produced commercially in South Africa, namely chrysotile, amosite, and crocidolite. Chrysotile and amosite samples were relatively pure while in contrast the crocidolite dust was found to consist mainly of ironstone and silica and contained less than 10% of asbestos fibre. Guinea-pigs, Vervet monkeys, and rabbits were exposed to these dusts. The results were assessed on histological criteria. It was found that, in all three species of animals, the amosite dust produced more marked lesions than the chrysotile and that these lesions occurred at an earlier period. It was not possible to compare these lesions with those caused by the crocidolite dust, owing to its impure nature. It was noted, however, that this dust caused severe lesions in guinea-pigs and monkeys and that the animals in this group succumbed more readily to respiratory infections.

In plain English

This 1963 report described animal experiments in Johannesburg. Guinea-pigs, Vervet monkeys and rabbits breathed mill dusts of the three asbestos types produced commercially in South Africa: chrysotile, amosite, and an impure crocidolite dust that was about 50% quartz and less than 10% crocidolite. The animals were dusted eight hours a day, five days a week, and their lungs were examined under the microscope. Groups were small: 16 to 24 guinea-pigs, 2 to 4 rabbits and 3 or 4 monkeys. In guinea-pigs, amosite caused lung scarring (fibrosis) earlier than chrysotile. Chrysotile-exposed guinea-pigs began dying of right-sided heart failure from the twenty-second month. Amosite caused fibrosis in monkeys and rabbits, while two rabbits exposed to chrysotile showed no significant change. The author could not compare lung lesions from the crocidolite dust with those from the other dusts, because the dust was impure and many of these animals died of bronchopneumonia. The author nevertheless noted severe lesions in guinea-pigs and monkeys and more respiratory infections in this group. The author concluded that amosite caused marked asbestosis in all three species and called the work preliminary.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal inhalation experiment: three dust exposure experiments, assessed by histology. The author described them as preliminary investigations.
• Who was studied: Guinea-pigs and rabbits from the stock of the South African Institute for Medical Research, and Vervet monkeys captured in the coastal forests of Natal, studied at the Pneumoconiosis Research Unit, Johannesburg. Chrysotile experiment: 24 guinea-pigs, 2 rabbits, 3 monkeys. Amosite experiment: 16 guinea-pigs, 4 rabbits, 3 monkeys. Impure crocidolite experiment: 16 guinea-pigs, 2 rabbits, 4 monkeys.
• Exposure: Inhaled mill dusts taken from the collecting bags of the mills' cyclone exhausts, given eight hours a day, five days a week. Fine chrysotile came from a mine in Swaziland (average 37,600 particles per ml). Amosite came from a Transvaal mine (average 30,000 particles per ml); the surviving amosite rabbits and monkeys were removed from dust after 14 months. A very impure crocidolite dust came from a mill in the North Western Cape Province; x-ray diffraction found it contained 50% (plus or minus 10%) quartz and less than 10% crocidolite (average 30,000 particles per ml).
• Main results:
  • Guinea-pigs exposed to chrysotile: collagen first appeared in the bronchiole walls by the eighth month, and there was definite generalized interstitial fibrosis by the fifteenth month. From the twenty-second month the animals began dying in right ventricular failure with marked diffuse interstitial fibrosis.
  • Guinea-pigs exposed to amosite: changes were seen earlier than with chrysotile. Reticulin increased from the third month, collagen had appeared by the fifth month, and diffuse interstitial fibrosis was seen at the twelfth month.
  • Guinea-pigs exposed to impure crocidolite: only four animals survived six months of dusting. Because of a very high rate of bronchopneumonia, their lesions could not be compared with those of the other experiments. Sections from non-infected lung showed lesions developing in a similar way to those from amosite.
  • The author reported that the impure crocidolite dust caused severe lesions in guinea-pigs and monkeys, and that animals in this group succumbed more readily to respiratory infections.
  • Monkeys exposed to chrysotile survived 7, 10 and 22 months. The 22-month monkey had cor pulmonale and localized fibrosis around some larger bronchioles. The author noted that similar pathology was seen in a monkey exposed to amosite for only four months.
  • Monkeys exposed to amosite: the monkey that died at four months had features comparable to a slight degree of human asbestosis. The monkey that died at 12 months had features consistent with a moderate degree. The monkey exposed for 14 months, which survived four more months, had features consistent with a moderate to marked degree of human asbestosis.
  • Monkeys exposed to impure crocidolite: all four died of bronchopneumonia, at 4, 6, 7 and 10 months. The 10-month animal had interstitial fibrosis, slight pleural thickening and two early asbestotic plaques over the left lower lobe.
  • Rabbits: the two chrysotile-exposed rabbits showed no significant change in the interstitial tissues. Three amosite-exposed rabbits were dusted for 14 months, then rested, and survived a further 2, 8 and 28 months. They showed interstitial fibrosis, marked and generalized in the fourth animal. Both crocidolite-exposed rabbits died of widespread bronchopneumonia.
  • Asbestos bodies were scanty and usually segmented in chrysotile-exposed animals. They were plentiful and rarely segmented in amosite-exposed animals, where fibres were extremely numerous.
• The authors' conclusion: The author concluded that chrysotile produced severe lesions in guinea-pigs, slight fibrosis in monkeys and no significant effect in two rabbits. In the author's view, amosite caused marked asbestosis in all three kinds of animals, more rapidly in guinea-pigs than chrysotile did, with an indication that the disease is progressive in monkeys and rabbits. The author found that the impure crocidolite dust caused severe disease in guinea-pigs and more respiratory infection, and suggested this might be due to its high quartz content.
• Limitations the authors state:
  • The thermal precipitator used to measure dust is not ideal for fibrous dusts, because the longer fibres are not drawn into the instrument. Dust counts also varied from day to day, with occasional peaking.
  • Because the crocidolite dust was impure and the animals had high rates of bronchopneumonia, its lesions could not be compared with those of chrysotile and amosite.
  • The experiments were preliminary investigations. The author noted that later studies would be conducted on a statistical basis, with chemical analyses of the lungs and better characterization of the dust clouds.
  • The normal range of heart weights has never been calculated for this species of monkey, so cor pulmonale was presumed from the heart findings.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Chrysotile, Amosite, Crocidolite.

Related studies

• Tumorigenic effect of fibrous dusts in experimental animals — F. Pott, F. Huth, et al. (1974)
• The carcinogenicity of dietary acrylamide intake: a comparative discussion of epidemiological and experimental animal research — J.G. Hogervorst, B.J. Baars, et al. (2010)
• Asbestosis in non-experimental animals in South Africa — I. Webster (1963)
• The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals — J.M. Davis (1970)
• Mesothelial proliferation due to asbestos and man-made fibres. Experimental studies on rat omentum — J. Friemann, K.M. Müller, et al. (1990)
• The relationship between fibrosis and cancer in experimental animals exposed to asbestos and other fibers — J.M. Davis, H.A. Cowie (1990)

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