geography of disease

There are certain diseases in China that show unique environmental characteristics. This particular focus is part of medical geography which studies the spatial variation of health and disease in any population and which searches for explanations for such geographical trends. To do this the epidemiological measurement of ‘prevalence’ has proven useful: it refers to the number of people in an area having a particular health problem during a defined period of time (e.g. one year). A bone illness that primarily affects children and young people, Kashin-Beck disease cuts a large swath across China. It is sometimes called ‘big-bone disease’, and areas of its high prevalence form a crescent running from the Tibetan plateau through China into eastern Siberia. The lack of normal levels of selenium in the soil is suspected of being a major factor in the aetiology of this disease. It is also thought that in Tibet it is related to the presence of fungi in damp stored barley, the staple diet. Once the seeds are contaminated the fungi spread through the new crop, and the cycle continues. Keshan disease is associated primarily with children between the ages of two and ten. Characterized by enlargement of the heart and fluid in the lungs, it is often fatal. Once again, the map of high prevalence of Keshan disease corresponds almost perfectly to the map of areas of low selenium in the soil.

But the biggest killer at the threshold of the new century is tuberculosis; epidemiologists say that at least a third of the population is infected with this debilitating affliction, including 6 million who have the active form of the disease. A quarter of a million Chinese die each year from pulmonary tuberculosis. One of the outstanding features of this contagious disease is that its prevalence appears to always be higher where people are concentrated in close proximity to each other. However, clearly this is not the only health problem that has to be dealt with. For example, lung cancer is increasing in China by 4.5 per cent each year, and a million are expected to die from the disease by 2025. Not unrelated to this trend is increasing cigarette consumption and the fact that close to 2 per cent of all cultivated land is devoted to tobacco production. On other fronts, while overall cancer rates are relatively low in China, stomach cancer is a major exception. Its yearly incidence (i.e. new cases) in China is just over 90 per 100,000 compared, for example, with 6.5 per 100,000 in the USA. It is thought that high rates of stomach cancer are related to the use of vegetables preserved through fermenting and salting. HIV/AIDS (see HIV/AIDS and STIs) is a literal time-bomb: an official Chinese estimate in 2001 was 50,000 cases, whereas the WHO estimated twelve times as many and projects 10 million for 2010. In one area of Henan province, for example, close to 20 per cent of villagers had HIV, and among those who had sold blood to illegal traders over 40 per cent were infected. Another consequence of unsafe use of injections is the hepatitis epidemic in China which contributes to more than 200,000 deaths annually due to liver cancer, the highest number of all deaths related to cancer.

PETER M.FOGGIN