Tropical medicine has been notoriously difficult to define because so few illnesses are limited to the tropics, and so many are found there. Be that as it may, tropical medicine is concerned mainly with a number of parasitic and other infectious diseases that are responsible for major health problems in low-income tropical countries. For example, malaria causes one million deaths per year, mostly in children under five in Africa. In certain villages of Zaire and Angola, trypanosomiasis (sleeping sickness) affects 70-80% of inhabitants. Leprosy is synonymous with stigma, and new treatment regimens offer hope that it will soon be controlled. But it still afflicts between one and two million people in the world, mostly in Asia, Africa, and Latin America. Fifteen million poor people in 73 countries suffer from gross enlargement of the limbs, a symptom of chronic filarial disease.

Many of these so-called tropical diseases also...