Leprosy deserves separate discussion for two reasons. First, although not all those afflicted by it were poor, many were. They provide valuable evidence of the nature of poverty in Africa, and their care was a special concern to Africans and Europeans. Second, the treatment of leprosy passed through phases which paralleled approaches to poverty in Africa generally and enable these to be seen more clearly: a diversity of pre-colonial attitudes; neglect or ruthlessness in the early colonial period; generous but ideologically coloured concern between the wars; scientific optimism in the late colonial period; and divergent trends following Independence. Leprosy brings into high relief the scale and tenacity of African poverty, the dedication of those relieving it, and the courage of its victims.

Leprosy is caused by a micro-organism which chiefly affects the skin, eyes, certain peripheral nerves, and the mucous membranes of the nose and throat. It can be transmitted from one person to another, although the means of transmission are unclear. It is not hereditary, but natural resistance may be in part hereditary; this, together with shared environment and opportunities for infection, explains why leprosy seems often to ‘run in families’. Natural resistance is high in most adults, so that leprosy is less infectious than many diseases, but a minority of people are susceptible, especially in childhood. The strength of an individual patient's resistance probably determines whether he suffers active lepromatous leprosy, which is infectious, or tuberculoid leprosy, which is not infectious and is the more common in Africa.