USIA Washington File - December 15, 1999

Washington -- AIDS researchers report that little scientific evidence supports the recently publicized suggestion that the origin of the human immunodeficiency virus (HIV) that causes AIDS can be linked to an early oral polio vaccine tested on about a million people in central Africa between 1957 and 1960.

The hypothesis, published in a recent book by British journalist Edward Hooper, suggests that HIV-1 -- the virus responsible for the global AIDS pandemic -- originated as a result of the inadvertent inoculation of trial participants with an HIV-like virus present in monkey kidney cell cultures used to prepare the polio vaccine.

The suggestion first appeared in a 1992 Rolling Stone magazine article that sought to link AIDS and the polio vaccine trials in Africa.

A spokesman for the U.S. Centers for Disease Control and Prevention in Atlanta, Georgia, said that the weight of scientific evidence "does not support this idea, and there is no more reason to believe this hypothesis than many others which have been considered and rejected on scientific grounds." The spokesman said that the same oral polio vaccine that was used in central Africa was also tested on thousands of individuals in Poland, but there was no evidence of early HIV infection there. He added that since the 1960s, billions of doses of oral polio vaccine have been delivered worldwide and no association with HIV infection has ever been recorded.

Researchers report that most scientists have long believed that the AIDS virus descended into humans from a primate species. But up to now there had been scant data to support the thesis, allowing theories such as the polio-virus vaccine hypothesis to flourish. Last January, however, an international team of scientists identified a subspecies of chimpanzees native to west equatorial Africa as the original source of the AIDS virus. The discovery was hailed as the best case yet for the AIDS virus jumping from chimpanzees into humans.

The findings were announced at the opening of the largest annual AIDS conference held in the United States and published in the February 4 issue of Nature.

The research team, led by Dr. Beatrice Hahn of the University of Alabama in Birmingham, found through careful molecular analysis that a certain strain of chimpanzee virus is closely related to human HIV-1 infections that cause AIDS. This virus strain infects one particular chimp subspecies, called Pan troglodytes troglodytes, found in a region that includes Gabon, Cameroon and Equatorial Guinea.

Significantly, Dr. Hahn and her colleagues also found that the natural habitat of these chimpanzees "coincides precisely" with the regions in Africa that have had human HIV-1 infections for the longest period of time. The scientists conclude that this particular subspecies of chimpanzees is the natural reservoir of HIV-1, and cite conclusive evidence that the virus has spread from the chimpanzees to humans on three distinct occasions.

The researchers believe that HIV-1 was introduced into the human population when hunters became exposed to infected chimpanzee blood. Furthermore, they speculate that humans might still be at risk from cross-species transmission because the so-called bushmeat trade -- the hunting and killing of chimpanzees and other endangered animals for human consumption -- is still common practice in west equatorial Africa.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which helped fund the research effort, said the findings had "significant potential." "We now have chimpanzee isolates of simian immunodeficiency virus (SIV) that have been shown to be closely related to HIV-1," he said. "Furthermore, this virus infects a primate species that is 98 percent related to humans. This may allow us...to study infected chimpanzees in the wild to find out why these animals don't get sick, information that may help us better protect humans from developing AIDS." Dr. John Moore, a lead researcher at the Aaron Diamond AIDS Research Center in New York, said it is widely accepted that humans became infected with HIV-1 through contact with chimpanzees. He said the question is how did it get from chimps to humans? "Certainly, the view that has the most credibility in the AIDS research community is that it is a natural transmission event," he said. "When animals are captured and butchered for human consumption -- and chimps are used as food in several parts of Africa -- it is not too difficult to imagine that you would cut yourself during the food preparation and virus transmission would occur. No one can prove it happened, but it's certainly the most immediately sensible idea." Moore said, however, that Hooper's theory that a polio vaccine produced in cultures of kidney cells from various primate species could have been contaminated "by some strange set of circumstances" with a virus that was later identified in humans as HIV-1 "is extremely unlikely." "It's not 100 percent impossible, but it's highly, highly unlikely," Moore said. "He really has no evidence other than speculation and coincidence to support his case." Researchers also point out that different subspecies carry different forms of the chimp virus and, if current research is correct, the subspecies of chimp from central Africa whose kidneys might have been used in the polio vaccine trials are the "wrong" ones -- harboring only a distant relative to HIV-1.

The Wistar Institute, the private, non-profit organization that produced the 1950s polio vaccine used in Africa, said it would allow two independent laboratories to test material from the vaccine trials in hopes that this will end the controversy by showing no evidence of the chimpanzee form of the virus that causes AIDS. Wistar said the labs are expected to receive the material by the end of the year.

In 1995, Swedish scientists tested some of the vaccine used in Africa and found no evidence of either the simian or human immunodeficiency virus. However, the Swedes looked at only one of two batches involved in the production of the vaccine, and the new tests will encompass both. Experts report, however, that negative results from the tests will not necessarily resolve the controversy because other batches, either used up or lost since the vaccine trials in Africa, might have been contaminated.

Two Wistar scientists who led the polio research in Africa, former institute director Hilary Koprowski and his former deputy Stanley Plotkin, reject the suggestion that the vaccine could have been the medium of transfer.

Koprowski said chimpanzees were used only to test the vaccine and never to produce it. Instead, researchers made the vaccine with kidney tissues from Asian rhesus macaque monkeys, whose kidney cells do not support SIV or HIV.

"This book has only preconceptions. There are no facts," said Koprowski, now professor of microbiology and immunology at Thomas Jefferson University in Philadelphia.

"The idea is a house of cards built on circumstantial evidence, and whatever doesn't fit has been ignored," said Plotkin, who developed the modern rubella vaccine before leaving Wistar for France's Pasteur Merrieux Connaught. "It's also, frankly, an attack on people's reputations, and I feel it has to be dealt with." The Wistar Institute faced similar assertions in 1992, when Rolling Stone magazine published an article on the polio-AIDS theory. At the time, the institute formed an outside panel of scientists who concluded that the polio trials has not been responsible for the spread of AIDS.

(The Washington File is a product of the Office of International Information Programs, U.S. Department of State)