Besides trying to the find the most effective methods to treat and prevent HIV/AIDS, Dr. Max Essex, Chair of the Harvard AIDS Initiative, has been trying to understand why southern Africa is the epicenter of the epidemic. According to the 2010 UNAIDS Report, 22 million of the 33 million people living with HIV live in sub-Saharan Africa. In South Africa the adult HIV prevalence is 17.8%, with an estimated 5.6 million people living with HIV. In three other southern African countries, the national adult HIV prevalence rate now exceeds 20%. These countries are Botswana (24.8%), Lesotho (23.6%) and Swaziland (25.9%). Spotlight Editor Martha Henry asked Essex about what he and his HAI colleagues have learned.
Spotlight: Your recent paper in AIDS showed that about 30% of people acutely infected with HIV-1C, the subtype predominant in southern Africa, maintain a high viral load for a much longer period than was expected. People with a high viral load have a much greater chance of infecting a partner. Does this finding explain why the AIDS epidemic is much worse in southern Africa than elsewhere? Is this the smoking gun that researchers have been looking for?
ESSEX: Researchers don’t like to use terms like “smoking gun” because we’re wary about raising expectations higher than other people might interpret as justified based on the evidence. But yes, it’s certainly the most logical way to explain why the epidemic in southern Africa is much worse in terms of total number of people infected than the epidemics anywhere else in the world.
How can you tell if the severity of the epidemic in southern Africa is due to a biological difference in HIV-1C rather than behavioral differences in people, such as social migration patterns or concurrent (overlapping) sexual partners? Is it possible to tease apart whether it’s biology or behavior or some combination of the two?
ESSEX: In wanting to find an explanation for the severity of the epidemic in southern Africa, we thought a difference in the virus was a logical place to look. Admittedly I’m a virologist, so I think of the virus first.
I have no doubt that behavioral issues like the absence of circumcision and multiple concurrent partnerships can contribute to higher rates of infection, but I think the explanation that makes the most sense is that those differences are in addition to the virus’s ability to spread based on viral load. Behavioral factors may make spreading or transmission worse, but without this significant difference between viruses, they just increase transmission by 50 or 100%, not five-fold, the way the differences really are in southern Africa versus other parts of Africa.
Unlike the AIDS epidemic in the U.S., which is predominantly among men who have sex with men and are infected with HIV-1B, the epidemic in southern Africa is predominantly a heterosexual epidemic with both men and women infected with HIV-1C. Why the difference?
ESSEX: The difference in transmission ratios with respect to viral subtypes that I think is clearest to document but hardest to explain is why HIV-1B, the subtype that caused the epidemic in the U.S. among gay men and IV drug users, doesn’t have much of an ability to infect women any place in the world. There’s no evidence that I’m aware of anywhere—South America, Haiti, etc.—that HIV-1B has had the same degree of efficiency in infecting women as any of the major viral subtypes that have caused the heterosexual epidemic in Africa.
And so what I would predict is that, for whatever reason, HIV-1B doesn’t get produced in cervical vaginal fluids or female reproductive tract fluids or infect through cells of the female reproductive tract as well as does HIV-1C, the subtype predominant in southern Africa. It’s that ability, the ability of the virus to infect cells in the reproductive tract, especially the female reproductive tract, that I think would be different with the different viruses.