4. Asbestosis
Fine asbestos fibres, once down in the lung, are not readily removed. In fact, in sufficient numbers they are able to damage the scavenging cells that arrive to remove them and this leads to a process of 'healing' by scar formation or fibrosis.
Unfortunately, scar formation in the lung destroys useful lung tissue and ultimately may result in sufficient damage to impair the lung's ability to take up oxygen. This leads to the person becoming short of breath and, as the disease progresses, may be responsible for his or her death.
Figure 4 A section through a lung of someone who had asbestosis
It takes prolonged high exposure to cause asbestosis and so it is a disease that is really only found amongst people who worked with asbestos for several years. It is dose-related; that is very high exposures, such as occurred before the 1950s, could produce the disease in 3 or 4 years, but lower exposures may take more than a working lifetime to cause asbestosis. Hygiene standards developed in Britain in the 1960's aimed to keep the fibre levels so low that very few exposed workers developed the disease even after 40 years of working with asbestos.
In 1985, Sir Richard Doll and Julian Peto1 reviewed the evidence for health hazards associated with asbestos and as far as asbestosis was concerned they concluded that there was a threshold of cumulative exposure below which clinical disease did not occur. They judged that this threshold was about 25 fibres/ml.years (that is an exposure equivalent to 25 years at 1 fibre/ml, 10 years at 2.5 fibres/ml, and so on). It is still believed that the threshold for asbestosis for most people is around this level.
The first evidence of disease is shortness of breath. At that time, the chest X-ray film or chest radiograph will show irregular shadows at the bottom of the lungs and doctors will be able to detect crackling noises through the stethoscope at the lung bases. Later, the ends of the fingers and toes become abnormally rounded, like drumsticks (called 'clubbing'). Today, physicians may use CT scans to help get a more precise diagnosis of asbestosis.
Once the disease has started, it usually progresses slowly, though there is some evidence that it may stop progressing if it is detected early and the person is removed from further exposure. It sometimes appeared for the first time after the person had left the asbestos industry. As there is no known treatment and the disease is definitely progressive if found late, early detection is essential and all asbestos workers should have regular medical surveillance.
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