Silicosis and silicotuberculosis amongst small scale gemstone miners in Northern Tanzania

Worldwide, some 46m people work in 'artisanal, small scale mines' (ASM), a number far larger than the 7m employed in large scale mining. ASMs are located exclusively in resource-poor countries, are locally owned, unregulated and use manual methods of extraction - but collectively produce up to a quarter of global minerals and precious metals. While artisanal mining may be a route out of poverty, the risks of such work are high, yet almost entirely unmeasured.

A recent review of research topics in studies of ASM, concluded that more research was needed, particularly of infectious (such as tuberculosis) and respiratory diseases.

Silicosis is an incurable lung disease caused by the inhalation of crystalline silica in activities such as hard rock mining. It generally develops slowly, but when levels of silica are very high there may be a far more rapid onset with early respiratory failure and death. Importantly, silicosis increases the risk of tuberculosis (TB) by about four-fold and miners often contract the disease in addition to silicosis.

Tanzanite is a gemstone exclusively found in Mererani, northern Tanzania, and mined in deep shafts using ASM methods by around 10,000 workers, across about 100 mines. Their exposures to silica appear to be very high, and there is suggestive evidence of very high rates of aggressive silicosis in young miners with fewer than 5-years of employment. Similarly, their rates of TB are high, as are those in the local non-mining community.

There is concern that efforts to control TB in the area are hampered by transmission of the disease within mines, and between miners and their local contacts.

I aim to measure, across time, the development and progression of silicosis and TB in tanzanite miners and determine how much these have an impact on their health and their ability to earn a living. In addition, I will examine whether the spread of TB from miners to the local community is common.

To do this I propose two studies. In the first, I will recruit and follow a group of 410 miners from a selection of 10-16 mines. In them, I will make measurements of their lung function and symptoms, and perform TB tests and chest x-rays (to detect silicosis) at the beginning of the study and then again after 18 months.

In a second study, I will use 'whole genome sequencing' (WGS) to identify particular strains of TB in miners with the diseases; I will use the same technique in individuals discovered to have TB through a local community screening program. WGS is technique that that allows for entire genetic codes of an organism to be read. It will allow me to identify which strains of TB are present in the population while checking for resistance to treatments, and, crucially, to map transmission between individuals.

This work will be done in collaboration with the infectious disease team at the Kibong'oto Infectious Diseases Hospital, the National TB hospital of Tanzania, taking advantage of their ongoing TB screening programme and close relationships with the local ASM community. To assist with study management and to enhance impact, I will convene a study Advisory Board of stakeholders including our collaborators at the National TB and Leprosy program, expert academics, and representatives from the local mines and from organisations for persons previously treated for TB.

This novel work concerns the intersection between occupational and infectious diseases and should produce findings that will be of importance in the prevention of both - in a sector that is of growing, global importance.