The SIV Connection

November 3, 2001

Heather Heilman
Phone: 865-5714

Four years ago, on a flight from New York to New Orleans, Preston Marx was seated near a man who was reading an article about one of Marxs colleagues. The two men struck up a conversation, and the other passenger introduced himself as Ernest Drucker. He told Marx that he did research on how HIV was spread by intravenous drug users. Marx, a professor of tropical medicine at Tulane, realized he had just met the perfect audience for an idea hed been tossing around in his head. I think needle reuse is responsible for the very origin of the AIDS epidemic, he told Drucker. Of course, Drucker said. Needles spread it around. No, Im saying we would never have had AIDS in the first place if there hadnt have been needle reuse, Marx said. What do you mean? Drucker asked. In the 1980s, researchers at Tulanes Regional Primate Center noticed that one of the species they kept, sooty mangabeys, were infected with something that looked a lot like HIV. They werent sure if the animals had inadvertently become infected in an experiment or if they were naturally infected. Preston Marx traveled to the animals natural range in Liberia and Sierra Leone, where he discovered that both wild monkeys and those kept as pets were widely infected with a virus similar to HIV-2. Before long, different groups of researchers were finding that primates across the entire African continent were infected with different versions of SIV (Simian Immunodeficiency Virus). That tells you its old. It could not have been recently disseminated, Marx said. If you look at the evolutionary distances between the different strains, you can do calculations that show SIV is hundreds of thousands or millions of years old. That means that for thousands of years, people in Africa were eating SIV-infected primates and keeping them as pets. So why didnt the AIDS epidemic happen sooner, Marx wondered. When Marx discovered that pet monkeys were infected with SIV, hed expected to find pockets of HIV in rural Africa that were caused by directly catching the virus from monkeys in the same way humans might catch rabies from an animal. But the number of such cases that he found were extremely smallonly 2 cases out of 10,000 people who had been exposed to SIV. I said to myself, we have a missing epidemic here, Marx said. Researchers at the primate center had observed that when they serially infected monkeys with HIV, using the same needle to spread the disease from one animal to the next, the virus becomes increasingly more virulent. When humans are exposed to SIV, the result is usually a weak and short-lived infection. Marx wondered if serial passage of the virus from person to person could have helped SIV become stronger and transform itself into HIV. In massive public health campaigns that took place in Africa in the 1950s, millions of people were injected with vaccines and antibiotics in efforts to eradicate diseases like polio, smallpox, malaria and syphilis. More often than not, hypodermic needles were used repeatedly rather than being thrown away after one use as intended. Marx hypothesized that these well-intended programs had provided the means by which relatively harmless SIV turned into HIV. That could also explain why there are actually four distinct subtypes of HIV, which represent four separate crossovers from primates to humans. Something that never happened in thousands of years happened four times in the 1950s, Marx said. Something new had to be at work, and injection equipment is new. The chance meeting of Marx and Drucker on an airplane blossomed into a major collaboration. The two men gathered evidence to support their hypothesis and presented it at a conference on the origin of AIDS held in London in September 2000. An article about their idea appeared in The Atlantic. They will soon publish papers on their hypothesis in several journals, including The Lancet. Its usually difficult to publish a mere hypothesis, but this one seems compelling and plausible to many in the field. Marx and Drucker are working with scientists at Los Alamos National Laboratory to test their idea on a computer model. They also are working with 10 clinics in Central Africa to see if serial passage of SIV is still taking place. That becomes the important question, Marx said. If our idea is correct, we could be making new strains of HIV even now. In Africa, theres still a problem with things as simple as having an adequate supply of new needles.

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