Influence of Dusts on Tuberculous Infection

Our plain-English summary of Influence of Dusts on Tuberculous Infection, by A.J. Vorwald, A. Landau (1937).

The study

• Authors: A.J. Vorwald, A. Landau
• Published: Archives of Pathology. July 1937
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This was a laboratory experiment in white mice, carried out at the Saranac Laboratory. It tested whether dust deposits under the skin made tuberculosis bacteria more likely to settle and grow there. The dusts were 22 kinds, including forms of free silica, silicates and a few non-silica minerals. Asbestos minerals were not tested because suitable specimens were not available. Each of seventy mice usually received four 5-milligram dust injections under the abdominal skin, one of them a quartz comparison. Tuberculosis bacilli were later injected into a vein. In general, bacilli were more numerous, and often clumped, in lesions made by pure silica and by granite. In lesions made by silicates and non-silica minerals they were usually scattered and hard to find. Results were not consistent. No organisms were seen in carborundum lesions, and iron-containing minerals were an exception to the silica pattern. The authors concluded that dust high in free silica stimulates the growth of tubercle bacilli. They added that, except possibly for the free silica group, the numbers of observations were too small to be statistically significant. They also said the method was not altogether reliable.

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 experiment (mice given dust injections under the skin, then tuberculosis bacilli by vein)
• Who was studied: Seventy white mice in total, Saranac Laboratory, New York. Each mouse usually received four separate dust injections, including a quartz control.
• Exposure: Twenty-two dusts (forms of free silica, mixed dusts, silicates, and non-silica minerals such as carborundum and aluminum oxide), ground to 1 to 3 microns, 5 mg per injection under the skin, usually four injections per mouse including a quartz control. Asbestos minerals were not included.
• Main results:
  • Bacilli were generally more numerous, and often clumped, in lesions produced by forms of pure silica and by granite.
  • In lesions from silicates and non-silica minerals, bacilli were usually scattered and in most cases difficult to find, though this was not invariable.
  • When free silica was mixed with silicates in granite, all the lesions were positive for bacilli, with bacilli as numerous as or more numerous than in the quartz control.
  • Not a single carborundum lesion contained visible organisms.
  • The iron-containing minerals tested were a notable exception to the trend seen with silica.
  • The dose of bacilli had little effect on whether organisms were found in a lesion, and necrosis was not a determining factor.
  • Organisms were not found in lesions of mice killed within one week after the bacilli were injected.
• The authors' conclusion: The authors concluded that dust with a high content of free silica stimulates the growth of tubercle bacilli, confirming Kettle's view for pure crystalline silica. They did not confirm the converse view that combined silica and non-silica dusts have no effect.
• Limitations the authors state:
  • Except possibly for the free silica group, the number of observations on each mineral or group was not large enough to be statistically significant.
  • The inconsistencies suggested the method was not altogether reliable, and conclusions require large numbers of tests on the same material.
  • The assumption that intravenous injection spreads bacilli evenly to all parts of the body is debatable.

Topics

Medical terms in this study, explained in our Lexicon: Saranac Laboratory, Silicate, Asbestos.

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