Since HIV/AIDS was first diagnosed nearly 25 years ago, more money has been put into combating this disease than probably any other in human history. It's not hard to see why: no other disease has ever threatened such a devastating impact as it attacks the generation whose labor and child-rearing is pivotal to the functioning of any human society.
But the latest figures from UNAIDS ahead of World AIDS Day today showed that despite the billions of dollars (perhaps US$22 billion since the 1980s), prevalence in most of southern Africa is still rising -- Swaziland has now crossed the 40 percent mark, while Botswana, at 37 percent, is heading that way, and South Africa is close to 30 percent.
So just why has Africa been hit so hard? And why has all the money invested in prevention programs had so little success in Africa (apart from the striking and oft-cited exception of Uganda)?
Part of the answer to both questions was offered by 30-year-old Josina, in a clinic in Maputo, the capital of Mozambique, early last month.
Josina looked younger than her age despite being HIV-positive and having three children and another on the way. Dressed in a halter- neck T-shirt dress and woolly hat, she shyly explained her position.
Twice, she'd had boyfriends but they left her when she got pregnant; she now had a boyfriend, but he was in prison so she had found another boyfriend who had offered to help get him out. What she described was a network of relationships, sometimes overlapping, on which she relied to feed her children. Often she ended up abandoned or betrayed.
There are two characteristics to Josina's painful story which are replicated across Africa. First, what's known as "concurrence."
Research indicates that the number of sexual partners in Africa and the West is broadly similar, the difference is that across Africa, many men and some women have two, three or more long-term relationships at the same time, whereas in the West, the dominant pattern is of serial monogamy -- one at a time with the occasional one-off. The problem is that concurrence is uniquely susceptible to spreading HIV/AIDS; transmission is more likely to happen in ongoing sexual relationships than in one-off encounters, and once one person is infected, they will infect the whole network.
Second, concurrence is reinforced by inequality. In a country with high levels of poverty -- in Mozambique nearly 80 percent live off less than US$1.72 a day -- the deal offered by a truck driver or street vendor with some hard cash in his pocket can represent the best survival strategy for a woman.
This is a disease that is feeding off desperate poverty. If you're worried about where your child's next meal is coming from, or how you are going to avoid being thrown out of your shack for not paying rent, longer-term risks such as dying of AIDS carry little weight.
The plight of Josina and the millions like her is central to the battles that have been waged among experts for more than a decade.
The hope was that prevention was simply a matter of making Josina aware of the risks she is taking; information and free condoms would be enough to induce behavior change. But in many places it hasn't worked; Botswana has been swamped in condoms, but they've had little appreciable effect, as Helen Epstein, a molecular biologist at Princeton University, points out.