HIV Crossed to Humans 70 Years Ago, Analysis Says

The deadly human immunodeficiency virus that causes AIDS has existed in human populations for at least 70 years--far longer than most researchers had thought--according to a new analysis at Los Alamos National Laboratory using the world’s fastest computer.

The finding that the virus first jumped from chimpanzees into humans sometime around 1930 could provide epidemiologists strong hints about the future evolution of the epidemic--hints that could be valuable in the frenzied efforts to produce an AIDS vaccine.

It also apparently lifts a burden of guilt from researchers testing a polio vaccine in Africa in the 1950s. A September book by British science writer Edward Hooper, called “The River,” charged that the AIDS epidemic started when the researchers used chimpanzee cells contaminated by the virus to produce the vaccine.

But geneticist Bette Korber of Los Alamos told the seventh Conference on Retroviruses and Opportunistic Infections here Tuesday that the virus emerged long before those experiments began. She reached that conclusion by comparing the composition of the genetic material of the many current strains of the virus and extrapolating back to a common origin.

Her approach is a well-recognized technique that has been used to determine when different species diverged from a common ancestor. Similar studies of human mitochondrial DNA also have identified a common female ancestor of modern humans, called “Eve,” who migrated out of Africa sometime between 100,000 and 200,000 years ago.

Some researchers are calling Korber’s species-leaping HIV a viral Eve.

The oldest known blood sample containing HIV dates from 1959, so some scientists have assumed that the virus must have entered the population a few years before then.

Others, however, believe that the virus most likely was present in human populations for many years, perhaps even decades before. Korber’s study seems to uphold the latter viewpoint.

Korber and Los Alamos are the custodians of all the genetic sequence information on HIV generated throughout the world. When a scientist determines the sequence of a new variant of the AIDS virus, he or she sends it to Los Alamos for preservation and comparison to other viral sequences.

HIV mutates rapidly, which is why there are a growing number of variants of the virus now infecting humans. That rapid mutation rate is responsible for the ease with which HIV develops resistance to anti-AIDS drugs and may make it difficult to develop vaccines against the disease.

There now are eight major sub-types, or clades, of HIV-1--the most common form of the virus--circulating throughout the world and a much larger number of strains that vary only slightly from one another. HIV-1 is known to have originated in chimpanzees because of close sequence similarities to a chimpanzee virus. A less common form, called HIV-2, is known to have originated in sooty mangabey monkeys.

But to compare all the HIV-1 sequences and look for a common ancestor required the use of an extremely powerful computer. Los Alamos is the home of Nirvana, the world’s most powerful computer, able to perform more than 1 trillion calculations per second.

“They didn’t give me [the entire computer], but they did give me 512 nodes,” which was the equivalent of running her computations simultaneously on 512 computers, Korber said.

Using the computer to examine all those different sequences, she tried to determine the common ancestor of HIV. Then, she used two statistical techniques to estimate when that virus first appeared.

In both cases, she reached the same answer: The virus jumped from chimpanzees to humans sometime around 1930.

“This puts a much more precise date on the likely origin of HIV,” said Dr. Harold Jaffe of the Centers for Disease Control and Prevention.

How the virus jumped species is still an open question, although researchers suspect that it happened as a result of trapping or eating chimpanzees.

Historian Bruce Fetter of the University of Wisconsin at Milwaukee notes that the French colonial government used forced labor for massive infrastructure projects, such as the construction of the Congo-Ocean railway between 1921 and 1934 in what was then called the French Congo.

More than 20,000 workers on that project died, most from malnutrition, and it is not inconceivable that the workers who survived could have been driven by hunger to trapping and eating chimps, Fetter said. Coincidentally, the first outbreaks of HIV were seen in that region 30 years later.

Others note also that the early 20th century was characterized by sharply increased trapping of chimps for use in circuses and scientific research, bringing humans and primates into closer contact.

Researchers such as Beatrice Hahn of the University of Alabama suggest that HIV probably festered unrecognized in small communities--perhaps until it mutated into a more virulent form or perhaps until new routes of propagation became available in the 1950s.

The building of highways throughout the African continent offered one route for propagation by allowing infected truck drivers to carry the virus to other regions and spread it through sexual contact. Public health campaigns in which drugs and vaccine were injected by syringes were another.

Dr. Robin Weiss of University College in London attributes the spread to “needle abuse,” the practice of vaccinating or administering antibiotics to large numbers of people with only a few needles. “In the United States and Europe, antibiotics are given orally, but in Africa [during the 1950s] it had to be a shot,” he said.

In “The River,” Hooper charged that researchers from Philadelphia’s Wistar Institute used cultured chimpanzee cells to produce an experimental polio vaccine that they began testing in Africa in 1957. That charge has never been substantiated.

Hooper’s basic argument was that the first outbreaks of AIDS occurred in the same areas where the polio tests were conducted and that the first known case did not occur until 1959, only after the tests were completed. But the new findings, said CDC’s Jaffe, make Hooper’s hypothesis “rather unlikely.”

Jaffe also called Korber’s findings “a lesson for the future. If we continue to interact with primates, there is a potential for other nonhuman viruses to enter the population as well.”