WEDNESDAY, April 21, 2004 (HealthDayNews) -- For more than 15 years, scientists have tried to disprove a shocking theory that suggests a conspiracy involving the polio vaccine unleashed AIDS on the world.
Now, an international team of biologists has offered up more evidence that the idea is impossible.
In a report in the April 22 issue of Nature, the researchers debunk the idea that scientists in the 1950s inadvertently contaminated a polio vaccine for humans with an AIDS-like virus from African chimpanzees. According to the latest finding, the virus that currently infects chimpanzees in that region is far different from the monkey disease that developed into AIDS in people.
"This further warrants the safety of these vaccines and their use to eradicate disease, and should put people's fears to rest," said Clayton Buck, an associate director for academic affairs at Philadelphia's Wistar Institute, which was involved in the initial vaccine work.
However, it's not clear if the new study will sway skeptics who lean toward the vaccine contamination theory, first discussed in the late 1980s and then floated in an influential 1999 book. In fact, several regions of Nigeria have banned the polio virus because of concerns about its safety.
"I hope that this new finding, which is really devastating to the polio vaccine theory, will be taken on board by [believers]," said study co-author Michael Worobey, an assistant professor of ecology and evolutionary biology at the University of Arizona. "I guess I won't speculate on whether that will happen."
There's little doubt among scientists that AIDS originated in Africa by somehow making its way from monkeys or chimps infected with a disease called simian immunodeficiency virus (SIV).
But how did the virus make the jump from primates to people? The prevailing theory is that the blood of Africans came into contact with the blood of chimps, perhaps when people hunted, butchered, or ate the creatures. "Every day, there's opportunities for the virus to cross from the chimp population into humans," Worobey said.
Indeed, viruses often travel from animals to humans. Influenza viruses first begin in birds and find their way into humans, perhaps by making a stop in animals such as pigs.
But in his mammoth book, The River, author Edward Hooper popularized another theory, that scientists working in the Belgian Congo (now the Democratic Republic of Congo) grew a polio vaccine in chimpanzee cells infected with SIV. Hooper suggests vaccinated Africans then became infected with the simian virus, which mutated to become HIV.
The scientists involved in that study deny they used chimp cells, and in 2001 biologists released a barrage of studies that refute the polio theory. According to one of those studies, the remaining samples of the polio vaccine in question don't contain HIV or, for that matter, chimp cells.
In the new study, biologists report the results of their examinations of the genetic material in the feces of chimpanzees found in the region. Worobey gathered the feces during two dangerous trips to the Congo in 2000 and 2003. During the earlier trip, he developed blood poisoning and one of his companions, an evolutionary biologist named W.D. "Bill" Hamilton, died of malaria.
Only one sample was infected with SIV, and an analysis showed it's not directly related to HIV in humans.
Robin A. Weiss, a professor of viral oncology at University College London in the United Kingdom, said the research only serves to confirm, once again, that the polio vaccine theory is without merit.
"I don't know any scientists who take the polio/HIV theory seriously anymore," Weiss said. "I did once, but I no longer do. It is still a topic for discussion because some investigative writers and television producers do still take it seriously. Conspiracy theories, ghastly accidents, and furtive cover-ups make good copy even when refuted by scientific data."
But Weiss said research into the origins of AIDS is still necessary, especially considering that several diseases are currently linked to animals, including hantavirus, the Ebola virus, SARS, and mad cow disease. "Understanding why, when and how viruses jump host species is, I think, important," she explained.