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From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
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And I'm Melissa Block.
A quarter century after doctors first discovered a strange new disease called AIDS, scientists say they have pinpointed where it came from and they think they know when the first humans caught a chimpanzee virus that became HIV, the AIDS virus that has since infected 60 million people around the world.
NPR's Richard Knox has the story.
RICHARD KNOX reporting:
Researchers were pretty sure that HIV came from a virus ancestor that infected chimpanzees, but Beatrice Hahn of the University of Alabama says the scientific sticklers were unsatisfied with the evidence.
Ms. BEATRICE HAHN (University of Alabama): They said well there's still one other thing missing, because if you postulate that this virus is naturally infecting chimps and somehow got transmitted to humans, then there's got a be a reservoir out there where wild chimpanzees are infected with these viruses.
KNOX: In fact, no one had ever found the chimpanzee version of the AIDS virus, called SIV for Simeon Immuno Deficiency Virus, in a wild chimp. And it wasn't very common in captive chimps either. So Hahn and her colleagues set out eight years ago to track down the chimp virus in the wild. It was a tall order.
Ms. HAHN: It's not easy to get a wild chimpanzee to cooperate. They certainly will not stick their arm out and let you draw a blood sample.
KNOX: Hahn knew she could find the virus in urine, but that wouldn't work.
HAHN: In the truly wild situation, like in the forests of Cameroon or other places in West Africa, all you can collect is fecal samples. There's just no way you get close enough to these chimps which are under tremendous hunting pressure, that you would be able to collect urine samples.
KNOX: So the researchers devised a way to extract the virus from chimp droppings collected from the forest floor and to figure out how many chimps were infected, they had to invent a method of identifying individual chimps by the genes in those droppings. In effect they put a genetic bar code on each fecal sample.
The researchers looked where they thought the ancestor virus might be in the dense forest of southern Cameroon. They retrieved hundreds of fecal samples from 10 chimpanzee communities. Their results are published online today by the journal Science.
They found the chimp AIDS virus in 16 animals from five communities. Genetically the chimp viruses were a very close match to the human AIDS virus called group M for main.
Ms. HAHN: By finding a group of chimpanzee viruses that was very closely related to HIV 1 group M viruses, we were able to hone in, if you will, to zero down on the area in the forest on the chimpanzees that must have given rise to the virus that is now spreading globally and basically has caused the AIDS pandemic.
Dr. ANTHONY FAUCI (US Government AIDS expert): I think the study really nails it down for us.
KNOX: Dr. Anthony Fauci is the US Government's top AIDS expert. He think the virus probably jumped to humans many times over thousands of years as people hunted and butchered chimpanzees.
Dr. FAUCI: No one knows for sure, but it is entirely conceivable that there were multiple dead ends before the societal conditions were ripe for the explosion of an epidemic of sexually transmitted disease.
KNOX: Based on gene mutation rates, other researchers calculate that the ancestor of the main AIDS virus first infected humans around 1930. Eventually, it made its way down the Sanha(ph) and Congo Rivers to Leopoldville, now Conchasa(ph), 550 miles downstream. That's when the earliest case of HIV was recorded in a man whose blood was drawn in 1959 for a malaria study.
In Conchasa, Fauci says, the virus found its opportunity in the tumultuous conditions of West Africa in the middle of the 20th century.
Dr. FAUCI: Dissolution of the family unit, having people separated from the family, people being separated in mines or in trucking, having multiple sexual partners, other sexually transmitted diseases, so that when you have that rare event where it does jump species, now you give it the opportunity to spread from person to person.
KNOX: Now that scientists have uncovered HIV's origin, does it tell them anything useful in battling the pandemic? Hahn says it should. First, she's looking at how a virus that doesn't harm chimps can infect humans and devastate their immune systems.
Ms. HAHN: We're hoping to get at that. We are trying to compare across the entire genome chimpanzee viruses and corresponding human viruses.
KNOX: Already, her group has found a tiny genetic change that occurs when the chip virus infects human cells and flips back when they put the virus back into chimpanzee cells. Work like that could offer new targets for HIV vaccines and drugs.
Hahn also says there's interest in using her fecal analysis methods in human AIDS vaccine trials to pinpoint exactly when a person gets infected with HIV despite being vaccinated.
Richard Knox, NPR News.