Distribution and Incidence

In the late twentieth century, leprosy occurs commonly only in tropical and subtropical regions, as indicated in Map VIII.80.1. There are at least 15 million lepers worldwide, most of them residing in Africa, South and Southeast Asia, and South America. However, this geographic distribution of the disease more likely reflects the poverty of these regions than it does the possibility that elevated temperatures and humidity facilitate infection. Despite cheap and effective medication (dapsone) to arrest the relentless progression of leprosy in infected individuals, the disease continues to spread in the rural regions of Africa, Southeast Asia, and the Indian subcontinent. Often because leprosy stigmatizes its victims socially, leading to loss of employment, alienation from family and community, and, ultimately, to confinement in a leprosarium, lepers deny infection or evade treatment as long as they can. In the process they ensure transmission of the disease to others. Leprosy is normally passed from one individual to another only with sustained exposure, but the disease continues to spread even in areas served by Western medical practitioners, because of the high social costs of early identification and treatment.

In the past, leprosy probably extended as far north as the Arctic Circle. Extensive paleopathological investigations of medieval gravesites thought to have belonged to leper colonies have produced evidence of leprosy among Danes and Norwegians of the thirteenth century. Interestingly, the distribution of leprosy in medieval Europe, like that of today, appears to have been rural, and the written or physical evidence of leprosy disappears with urbanization. The disappearance of leprosy in Europe historically progressed gradually northward from the urban Mediterranean areas of Italy and Spain. Cases of leprosy were still reported in England and Scotland during

Map VIII.80.1. Estimated endemicity of leprosy in the world, 1983. (From World Health Organization. 1985. Epidemiology of leprosy in relation to control: Report of a WHO Study Group. World Health Organization Technical Report Series 716. Ge-

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the fourteenth and fifteenth centuries, and the disease persisted in Scandinavia until the late nineteenth century, where Hansen discovered the bacillus that causes the disease.

One of the odd features of the geographic distribution of leprosy is the increased prevalence on islands or near seacoasts. Late medieval and early modern theorists even attributed the cause of the disease to an exclusively fish diet, an explanation now discredited. Undoubtedly the low infectivity of the disease and its association with poverty and poor sanitation contribute to the slow spread inland once leprosy is introduced into a region.

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