Photograph by Imke Lass
Beatrice Hahn has spent years tracking a predator that cannot be caged and cannot be seen: HIV, the virus that causes AIDS. Three years ago Hahn, a virologist at the University of Alabama at Birmingham, announced she had traced the most prevalent form of the virus, HIV-1, to related strains found among chimpanzees in west central Africa. Somehow the viruses spread to humans, sparking the current pandemic. Hahn's studies also alerted her to the spiraling trade in meat from wild animals, called bushmeat, which threatens chimps, gorillas, and orangutans and many other primate species with extinction. To mark World AIDS Day on December 1, Hahn discussed the latest insights into the disease with associate editor Josie Glausiusz. Why do we need to understand the origin of HIV?
More than 40 million people are now estimated to have HIV infection or AIDS. Any time you have a public health disaster of that magnitude, there comes a certain degree of curiosity just to know where it came from. And any type of information that helps us understand the biology of these viruses is useful. The more information you gain, the more rational design you can apply to vaccines or drugs. How did HIV first hop over from chimps to humans?
This question cannot be answered. All we can say with certainty is that SIV, the simian immunodeficiency virus carried by chimps in west central Africa, is the closest relative to HIV-1. We know that you don't get these infections by looking at the apes or by petting their heads. It would require blood exposure. And we know that bushmeat hunting is a traditional activity in these countries, and has been for hundreds, probably hundreds of thousands of years. So that's a plausible route of transmission. Why didn't transmission of the virus occur earlier?
It most likely did, but it did not spread in the human host because initial transmission and subsequent epidemic spread require different sets of circumstances. A constellation of situations were conducive to epidemic spread: a combination of virus, host and environment. What has been speculated to have contributed is urbanizationpeople meeting people more frequently in sexually promiscuous surroundings, where there are slums and possibly prostitution. Perhaps even medical needle use; non-sterile needles will certainly do the trick. And any combinations of these. How common is SIV infection in wild African primates?
We recently did a study in Cameroon on roughly 800 bushmeat samples or pet monkeys of sixteen different species, including mandrills, olive baboons, and agile mangabeys. Of these sixteen species, thirteen were found to be SIV-infected. It means that there is a plethora of SIV out there, with each one of these species having their own strain. On top of that is an increase in bushmeat hunting, and thus an increase in potential exposure to these viruses. What's the consequence of such exposure?
When a person infected with HIV-1 encounters a second, related SIV, a recombination event might occur: The genetic material from the two viruses could blend together, leading to novel varieties. The new forms could be more virulent, or less virulent; they could spread faster or slower. None of this has been documented. On the other hand, you don't want to just downplay it. Given the magnitude of the current AIDS pandemic, we feel it's certainly prudent to look into these questions. How bad is the bushmeat trade?
It is an enormous problem, and not just from the public health perspective. If hunting continues at current levels, within one decade chimpanzees and gorillas and orangutans will be wiped off the face of this earth. It will wipe out thousands of species. That is mind-boggling. The bottom line is, it's not sustainable. Why has there been such an explosion in this trade?
Because it has become a big business. It's aided by roads, trucks, and logging. When the loggers go into the forest, they need to eat, and then the hunters go and supply them with meat. In the past, you would have to hike in five days and hike out five days, and by the time you came back, the stuff was rotten. Now you stand on the side of the road, and you flag down a trucker, and the trucker takes the meat off your hands and pays you, and then sells it two hours down the road at the next market. Why has it been so difficult to make an AIDS vaccine?
HIV mutates constantly, so there are many strains out there. There is concern that this genetic variationamong other thingswill hamper vaccine production. One current approach is to make a "consensus vaccine" based on proteins that would trigger an immune response to many of those strains, not just one of them. Researchers are using computer programs to look at the sequences of today's viruses and then to infer what the last common ancestor of today's HIV looked like. You could then take that sequence and design the vaccine around it. Do you think we will we ever have an effective AIDS vaccine?
Yes, I do. The best minds in the world are looking at this, and they'll figure out a way. One has to understand that vaccine development is a long, protracted process, and HIV is a very tricky virus. There are several candidates in the pipeline, and it will take ten years or more to figure out whether they are useful or not. Has your experience working with HIV changed the way you think about the world?
Yes. I think I was totally naive about issues of conservation, and about the effects of poverty on people. That has changed. I have gotten a much deeper appreciation of the difficulties involving conservation. Primates are dear to my heart, and there are no easy solutions. It's not that people in west central Africa just love to eat monkey. They will eat monkey because they're hungry. It's also an economic opportunity. Maybe if we provide them with a true and meaningful alternative, they may just take it.