“The work she’s been doing is very exciting,” says Geoff Garnett, a professor of epidemiology at Imperial College London. He says the biology of the virus is probably similar everywhere, and differences in infection rates are most likely attributable to differences in sexual behavior. “I don’t think concurrency explains everything, but it is very interesting.”
Morris’s computer models do not consider that HIV-positive people are more likely to pass the virus on to others in the first few weeks or months following infection. The infectiousness of HIV varies with the concentration of the virus in the blood—the more virus there is, the more likely it will get into genital fluids and be passed on during sex. During the first few weeks and months after infection, a person’s blood teems with the virus. But then the immune system produces antibodies that attack HIV. Virus levels fall and may remain low for years, rising again when the person’s immune system eventually fails and AIDS symptoms appear. Some estimates suggest that a person who has been recently infected with HIV may be as much as 100 times more likely to transmit the virus to a partner than someone who has been infected for a long time. African-style simultaneous long-term relationships may therefore be even riskier than Morris’s models assume. If one member of a Ugandan sexual network becomes HIV-positive, the virus will spread very quickly to all other members of the network in a very short time.
One morning not long ago, I accompanied an HIV-prevention worker in Botswana named Willington Mongwa as he made his rounds in Old Naledi, a relatively poor neighborhood in the capital, Gaborone. We passed a bar in which about 15 people, most of them men, sat on tree stumps drinking beer made from distilled sorghum. I asked Willington if we could ask the drinkers some questions. We approached a group of three young men, and they offered us some of their beer and gratefully accepted the condoms we offered them. “How long will it take you to go through those?” I asked one man. “Let’s see, there are about 10 here, so it should take about 15 days.” I asked him how many girlfriends he had, and he told me he had three, one real girlfriend and two secret girlfriends. He had been seeing all three for at least two years. He used condoms with the secret girlfriends but not with the real one. How many secret boyfriends do those secret girlfriends have? I asked. He said he didn’t know, but you can never trust women, and that’s why he used condoms. And the real girlfriend? “As I said, you never know with women, but if she has other partners, I hope she uses condoms with them.”
Several other men I met had similar sexual arrangements. Most women I spoke to denied that they had partners other than their husbands or fiancés, but the men frankly assumed that women conducted their affairs much as they themselves did.
Botswana is a culture of migrants, where both men and women often spend time away from their homes and may have long-term relationships with different people in different places. The traditional form of wealth is cattle, which are kept on remote cattle posts. For centuries boys tended the cattle, and men visited the herds from time to time, leaving their wives behind. During colonial times, Botswana’s economy was tied to South Africa’s, and many men went to work in the mines and cities around Johannesburg. Since the 1980s, Botswana’s own urban centers have grown enormously, and the shuttling of both sexes between town and village has increased.
Even though Botswana is a relatively wealthy country by African standards, some 38 percent of the population is classified as poor. The government provides rations to the destitute, but many people told me they had experienced deprivation and unemployment. Women in Botswana generally work at low-wage jobs such as housecleaning, child care, or farming. As a result, girls and women are drawn into relationships with relatively wealthy men who help them and their families. These men may have several long-term female sexual partners at the same time—one or two in their home villages and one or two in town. Meanwhile, a woman may draw on more than one man to help pay her family’s bills.
Girls are particularly vulnerable. Roughly equal numbers of men and women in Botswana are HIV-positive, but the HIV rate is much higher among teenage girls than among teenage boys, although boys and girls become sexually active at roughly the same age. A study in 2001 found that 20 percent of girls in one region of Botswana had been asked by their teachers to have sex; half said they accepted, fearing lower grades if they said no.
