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Cameroonian scientist Judith Torimiro was studying at the London School of Hygiene and Tropical Medicine when Hahn's research hit the news, and she remembers a discussion among her fellow students. "They were talking about possible transmission when hunters butcher the meat, but then someone asked, 'What about eating?' And the next question was, 'Do they cook the meat?' 'Yes, of course,' I said. 'And I eat it. My mother used to make it.' " She pauses and, in an anguished voice, adds, "How could they ask if we cook the meat?"
The Italians eat carpaccio and the Japanese sushi, so the question was not necessarily racist. But given the continent's history, the question raises African suspicions. Those turn to hackles when Ammann makes statements such as "The colonial powers and the missionaries had managed to wipe out cannibalism. When do we start on 98.4 percent cannibalism?"
Such inflammatory rhetoric discredits AIDS science in the minds of many Africans. After all, if whites think eating animals is cannibalism and that Africans have sex with monkeys, how can anything they say be true?
Roy Mugerwa is the principal investigator of Africa's first AIDS vaccine trial. Even though the vaccine had already been tried in Europe and America, Mugerwa had to push for more than three years to launch the trial, and even had to appear before Parliament. He recalls that a common argument was: "White people say AIDS originated here, and now they're bringing this vaccine, which could make it worse." As the AIDS-vaccine debate was unfolding, the government announced an effort to eradicate polio from Uganda. In the cauldron of suspicion and fear, a radio broadcaster announced that the polio vaccine might be contaminated with live HIV. As a result, thousands of children were not vaccinated, leaving them vulnerable to being crippled. "Why," Mugerwa asks, "does the false tend to be more easily believed than the true?"
No one knows how often aids viruses leap the species barrier, but when they do, what often transpires is what happened to Subject 11008, as she is known in the scientific literature. A 52-year-old woman living in Sierra Leone who eked out a living by farming, Subject 11008 was one of 9300 people whom Marx screened for a virus called HIV-2.
A little-known fact is that there are two separate AIDS epidemics. The major onewhich has killed more than 16 million people, according to figures released this weekis caused by HIV-1. But there is another AIDS epidemic, much smaller and concentrated in West Africa, caused by HIV-2, a less virulent and less transmissible virus that, nonetheless, can kill. While HIV-1 almost certainly comes from chimpanzees, HIV-2 comes from the sooty mangabey monkey.
Subject 11008 tested positive for antibodies to HIV-2. But when Marx examined her virus, he found that it was quite distinct from any other known HIV-2, though still clearly within the family. It was what virologists call a different "subtype" or "clade," from the Greek for "branch." A "strain" generally indicates a small variation in the genetic code of virusesan HIV-positive person usually has several strains in his or her bodybut a subtype or clade is genetically much different. Scientists have identified 11 subtypes in the main group of HIV-1 and six subtypes of HIV-2. Subject 11008's virus was labeled subtype F. To this day, it has never been found in any other person.
What's more, subtype F is so genetically distinct that it very likely did not evolve from one of the common subtypes but crossed into humans, quite possibly into Subject 11008, who said she ate sooty mangabeys. "It's an example of a crossover virus that didn't get the help that it needs to become an epidemic," says Marx.
The origin of a virus and the origin of an epidemic are different. The first is purely biological; the other is both biological and social.
Viruses are parasites; they replicate only by hijacking the machinery of cells. So a virus that jumps species must must be able to operate in cells that are biologically different from those of its original host. If it can't replicate efficiently, it won't be able to spread from one person to another.
Many viruses can't. Hahn and renowned AIDS researcher David Ho studied another person infected with a unique subtype of HIV-2. That patient never exhibited symptoms; in fact, researchers were only able to extract fragments of the virus, footprints of its failed attempt to survive in humans.
But even if a virus can replicate efficiently, it might not spark an epidemic. In 1976, a Norwegian sailor who had been in West Africa died of a mysterious disease. His wife and one of his three children also succumbed, both with shattered immune systems. "Now, the Norwegians are very well organized," says Francois Simon, a French researcher who studies HIV's diver-sity, "so they kept tissue samples." Those samples tested positive for HIV-1; the Norwegian sailor is Europe's first known case of AIDS.
Yet despite the fact that his virus was obviously capable of spreading, it died with his wife and child. The viral subtypes that have terrorized the world are genetically very different from the sailor's virus. And yet his HIV was the same very rare variant that turned up more than a quarter century later in Zekeng's 26-year-old Cameroonian woman: Group O. In other words, it was a tiny, sputtering epidemic all its own. In parts of Cameroon, it now accounts for 5 percent of all HIV-1 infections.