The HIV Superhighway

By Helen Epstein
Sunday, November 25, 2007

Earlier this month, the pharmaceutical company Merck announced that its prototype AIDS vaccine, which cost millions of dollars to develop, actually makes people more susceptible to HIV infection. The frustrating search for a vaccine makes it easy to despair over the global AIDS crisis, especially in Africa, where more than two-thirds of people with HIV now live.

Ideally, science would provide a magic bullet that would knock out HIV. Failing that, most AIDS researchers would settle for another type of magic that would generate political will and spur people to have fewer sexual partners and to use condoms more consistently. We haven't found any such magic, but we may have found the next best thing. It isn't perfect, but it costs nothing and, unlike the Merck vaccine, it does no harm. This semi-bullet consists of information -- about the sexual networks that seem to let the virus spread so rapidly in Africa, and about what people there need to do to protect themselves.

Health officials increasingly recognize how important this information is, because they are running out of ideas about how to fight the AIDS epidemic. Although the U.N. AIDS program recently announced a steep downward revision of the number of infected people, especially in Asia, Eastern Europe and Latin America, this means only that the epidemic is even more concentrated in east and especially southern Africa than previously thought.

In Botswana, Lesotho, South Africa and Swaziland, about a quarter of adults are HIV-positive -- a number 10 times higher than anywhere else in the world. HIV testing and treatment are more widely available in Africa than ever before, and while this has extended many lives, it has had little effect on the incidence of HIV. Last year, three important studies showed that male circumcision can reduce HIV transmission by about 60 percent, but the practice is still rare on much of the continent. Condom use remains dangerously inconsistent, and strict abstinence-until-marriage-and-fidelity- thereafter is rare everywhere. Even under the new U.N. figures, 1.7 million Africans became infected last year.

Which brings us to our desperately needed, not-quite-magic bullet. It consists of an idea that first occurred to a small number of researchers working independently in the early 1990s. One of them, a young doctor named Christopher Hudson, was practicing at a London clinic for sexually transmitted diseases when he noticed something peculiar: Some diseases, such as genital warts, seemed to be more common in his white patients, whereas others, including gonorrhea, were more common in his black patients, many of them recent immigrants from the Caribbean.

When Hudson took sexual histories, he discovered that these groups of black and white patients, broadly speaking, behaved differently. Both groups had the same average number of lifetime sexual partners, but his white patients tended to engage in "serial monogamy" -- one partnership at a time -- whereas the black ones were more likely to have steady, long-term relationships with two or three people at a time.

Hudson had a hunch that these different patterns of behavior might help explain the spread of the different diseases. People with warts are infectious for years, but those with gonorrhea are infectious only for about six months. So if a "serial monogamist" who switched partners every year or two contracted gonorrhea, the disease probably would have run its course before he could pass it on to a new partner. But if a man with two long-term concurrent girlfriends contracted gonorrhea, he would spread it to both of them immediately -- and if either of those women had another long-term partner, she would spread it to him right away, too. In this way, gonorrhea could spread rapidly to large numbers of people.

If his "gonorrhea theory" was correct, Hudson realized, it would have profound implications for the spread of HIV -- a far more serious problem caused by a virus that happens to behave like gonorrhea but can't be cured with antibiotics. As a 2004 article in the Journal of Infectious Diseases noted, after contracting HIV, people are highly infectious for about a month, after which they are far less likely to transmit the virus to others.

By the early 1990s, it was clear that HIV was highly concentrated in eastern and southern Africa. Unlike the rest of the world, where the virus was mainly confined to "high-risk groups" -- mainly prostitutes, intravenous-drug users and gay men -- everyone in this region was at risk, from cabinet ministers to women selling vegetables on the street. Studies by the World Health Organization and others showed that the patterns of sexual behavior in this region were broadly similar to those of many of the black patients who came to Hudson's London clinic: On average, Africans had no more partners over a lifetime than people elsewhere, but they were more likely to have a small number of long-term partners at the same time.

In 1997, Martina Morris, now a sociology professor at the University of Washington, showed mathematically that sexual networks involving long-term overlapping partnerships could create a kind of "superhighway" for HIV, even if everyone in the network had few partners. By contrast, HIV spread very slowly through sexual networks involving one-partner-at-a-time serial monogamy.

Today, long-term overlapping sexual partnerships are widely acknowledged -- by the U.N. AIDS program, the U.S. Agency for International Development, the Centers for Disease Control and Prevention and a growing number of African governments -- to be major drivers of the epidemic, not only in Africa but also in the West. Even the government of South Africa, with its famously muddled AIDS policies, has acknowledged this. "We should all avoid having multiple and concurrent partners," Deputy President Phumzile Mlambo-Ngcuka said on last year's World AIDS Day. "Let us commit to being faithful by sticking to one relationship at a time."

But this awareness is dawning awfully late. Until recently, the policy and program documents of just about every public health agency working on AIDS prevention in Africa were silent on the HIV superhighway created by overlapping partners. Instead, most AIDS campaigns emphasized the dangers of typical "promiscuity," mostly prostitution and casual sex. Such approaches make sense in most of the rest of the world, but in the hardest-hit parts of Africa, as numerous studies have shown, most HIV-positive people contract the virus not from casual relationships but from girlfriends, boyfriends, husbands and wives. Even people with only one or two trusted long-term partners are at risk if one of those partners has another long-term partner who is on the HIV superhighway.

CONTINUED     1        >

© 2007 The Washington Post Company