Speeding HIV's Deadly Spread

A Lethal Mix of Causes

International experts long regarded Botswana as a case study in how to combat AIDS. It had few of the intractable social problems thought to predispose a country to the disease, such as conflict, abject poverty and poor medical care. And for the past decade, the country has rigorously followed strategies that Western experts said would slow AIDS.

With its diamond wealth and the largess of international donors, Botswana aggressively promoted condom use while building Africa's best network of HIV testing centers and its most extensive system for distributing the antiretroviral drugs that dramatically prolong and improve the lives of those with AIDS.

But even though the relentless pace of funerals began to ease in recent years, the disease was far from under control. The national death rate fell from the highest in the world, but only to second-highest, behind AIDS-ravaged Swaziland. Men and women in Botswana continued to contract HIV faster than almost anywhere else on Earth.

Twenty-five percent of Batswana adults carry the virus, according to a 2004 national study, and among women in their early 30s living in Francistown, the rate is 69 percent.

Researchers increasingly attribute the resilience of HIV in Botswana -- and in southern Africa generally -- to the high incidence of multiple sexual relationships. Europeans and Americans often have more partners over their lives, studies show, but sub-Saharan Africans average more at the same time.

Nearly one in three sexually active men in Botswana reported having multiple, concurrent sex partners, as did 14 percent of women, in a 2003 survey paid for by the U.S. government. Among men younger than 25, the rate was 44 percent.

The distinction between having several partners in a year and several in a month is crucial because those newly infected with HIV experience an initial surge in viral loads that makes them far more contagious than they will be for years. During the three-week spike -- which ends before standard tests can even detect HIV -- the virus explodes through networks of unprotected sex.

This insight explained what studies were documenting: Africans with multiple, concurrent sex partners were more likely to contract HIV, and countries where such partnerships were common had wider and more lethal epidemics.

A model of multiple sexual relationships presented at a Princeton University conference in May showed that a small increase in the average number of concurrent sexual partners -- from 1.68 to 1.86 -- had profound effects, connecting sexual networks into a single, massive tangle that, when plotted out, resembles the transportation system of a major city.

A second key factor helping the virus spread through southern Africa is low rates of circumcision. Before European colonialists arrived, most tribes in the region removed the foreskins of teenage boys during manhood rituals. Those rites, which were discouraged by missionaries and other Westerners who regarded them as primitive, have gradually declined as the region rapidly modernized.

Dozens of studies, including three experimental trials conducted in Africa in recent years, show that circumcised men are much less likely to contract HIV because the most easily infected cells have been removed.

These factors, researchers say, explain how North Africa, where Muslim societies require circumcision and strongly discourage sex outside monogamous and polygamous marriages, has largely avoided AIDS. They also explain why the epidemic is far more severe south of the Sahara, where webs of multiple sex partners are more common, researchers say.