Botswana seems an unlikely place for an AIDS epidemic. Vast and underpopulated, it is largely free of the teeming slums, war zones, and inner-city drug cultures that epidemiologists say are typical niches for the human immunodeficiency virus. Botswana is an African paradise. Shortly after gaining its independence from Britain in 1966, large diamond reserves were discovered, and the economy has since grown faster—and for longer—than that of virtually any other nation in the world. Education is free, corruption is rare, crime rates are low, and the nation has never been at war. Citizens are loyal: A visitor quickly learns that even mild criticism of anything related to Botswana is considered impolite. Yet this country, with all these advantages, has the highest HIV-infection rate in the world.

The virus has spread extremely rapidly in Botswana. Two decades ago, virtually no one there was HIV-positive. By 1992 an estimated 20 percent of sexually active adults were infected. By 1995 that proportion had reached one-third, and today it is roughly 40 percent. In Francistown, Botswana’s second largest city, nearly half of all pregnant women in the main hospital test positive for HIV. The picture in the rest of sub-Saharan Africa is nearly as dire. AIDS has killed Zulu nurses in South Africa, Masai teachers in Tanzania, Kikuyu housewives in Kenya, Pygmy elders in Uganda. HIV infection rates range from around 6 percent in Uganda to 39 percent in Swaziland.

Such numbers are