HIV Dates Back To Around 1900, Study Shows

[Bianca]

                                     HIV dates back to around 1900, study shows



     Genetic analysis of tissue specimen recently discovered in the Democratic Republic of the Congo

     leads researchers to believe the virus that causes AIDS has been present for more than a century.






By Mary Engel,
Los Angeles Times Staff Writer
October 2, 2008

A genetic analysis of a biopsy sample recently discovered in the Democratic Republic of the Congo has led researchers to conclude that the virus that causes AIDS has existed in human populations for more than a century, according to a study released Wednesday.

The study, led by evolutionary biologist Michael Worobey of the University of Arizona in Tucson, puts the date of origin at around 1900, which is 30 years earlier than previous analyses.


HIV-1, the most common form of the virus, is known to have originated in chimpanzees because of close genetic similarities to a simian virus. It now infects an estimated 33 million people worldwide.

But figuring out when the virus jumped species and became established in humans has been difficult. The first cases in the U.S. were recognized in 1981, and the oldest evidence of the virus is a 1959 blood sample taken from a man who lived in what was then the Belgian Congo.

To find the point of origin, the scientists relied on a well-recognized genetic technique to determine the mutation rates of different sub-types of the virus. With a known rate of mutation, researchers could then, in essence, run the clock backward to find the point where the different sub-types were the same. That common ancestor would represent the first appearance of the virus in humans before it mutated.


"The HIV virus evolves incredibly quickly," said geneticist Bette Korber of Los Alamos National Laboratory in New Mexico, who did an analysis in 2000. "Those mutations get passed on to the next individual. So we have that evolutionary pace to enable a look backward."

Korber's analysis compared the 1959 blood sample and modern samples. She traced their common ancestor to roughly 1931.

The new analysis, published in the journal Nature on Wednesday, added lymph node tissue from a woman who died in 1960 in the Belgian Congo. The tissue specimen was one of more than 800 preserved in ice-cube-size blocks of paraffin at the University of Kinshasa.

The researchers compared that sample with modern strains to determine its mutation rate. Then they matched that rate with the 1959 sample, tracing their common ancestor to between 1884 and 1924.

"I've been trying to track down old samples like this for quite a few years now," Worobey said. "As soon as you have that one other sequence from that same time period, it really snaps the whole evolutionary picture into sharp focus."

The researchers surmised that the creation of colonial cities around the turn of the century was the catalyst that allowed the virus to take hold.

Dr. Steven M. Wolinsky, a co-author of the study, said that colonial cities meant not just more potential hosts for viruses living in closer quarters, but also prostitution and other high-risk behaviors for transmitting the virus.

"Urbanization was probably the main trigger," said Wolinsky, an infectious diseases specialist at the Feinberg School of Medicine at Northwestern University in Chicago.

Jim Moore, an anthropologist at UC San Diego who was not associated with the study, said the fact that the virus could have spread unnoticed for decades is no surprise, given the mortality rates in Africa during the colonial period.

"The conditions then were horrendous in terms of how Africans were treated," he said. "People dying of AIDS would have been part of the background."



mary.engel@latimes.com

[Austin Heller]

NEW YORK — The AIDS virus has been circulating among people for about 100 years, decades longer than scientists had thought, a new study suggests. Genetic analysis pushes the estimated origin of HIV back to between 1884 and 1924, with a more focused estimate at 1908.

Previously, scientists had estimated the origin at around 1930. AIDS wasn't recognized formally until 1981 when it got the attention of public health officials in the United States.

The new result is "not a monumental shift, but it means the virus was circulating under our radar even longer than we knew," says Michael Worobey of the University of Arizona, an author of the new work.

The results appear in Thursday's issue of the journal Nature. Researchers note that the newly calculated dates fall during the rise of cities in Africa, and they suggest urban development may have promoted HIV's initial establishment and early spread.

Scientists say HIV descended from a chimpanzee virus that jumped to humans in Africa, probably when people butchered chimps. Many individuals were probably infected that way, but so few other people caught the virus that it failed to get a lasting foothold, researchers say.

But the growth of African cities may have changed that by putting lots of people close together and promoting prostitution, Worobey suggested. "Cities are kind of ideal for a virus like HIV," providing more chances for infected people to pass the virus to others, he said.

Perhaps a person infected with the AIDS virus in a rural area went to what is now Kinshasa, Congo, "and now you've got the spark arriving in the tinderbox," Worobey said.

Key to the new work was the discovery of an HIV sample that had been taken from a woman in Kinshasa in 1960. It was only the second such sample to be found from before 1976; the other was from 1959, also from Kinshasa.
Researchers took advantage of the fact that HIV mutates rapidly. So two strains from a common ancestor quickly become less and less alike in their genetic material over time. That allows scientists to "run the clock backward" by calculating how long it would take for various strains to become as different as they are observed to be. That would indicate when they both sprang from their most recent common ancestor.

The new work used genetic data from the two old HIV samples plus more than 100 modern samples to create a family tree going back to these samples' last common ancestor. Researchers got various answers under various approaches for when that ancestor virus appeared, but the 1884-to-1924 bracket is probably the most reliable, Worobey said.

The new work is "clearly an improvement" over the previous estimate of around 1930, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. His institute helped pay for the work.

Fauci described the advance as "a fine-tuning."

Experts say it's no surprise that HIV circulated in humans for about 70 years before being recognized. An infection usually takes years to produce obvious symptoms, a lag that can mask the role of the virus, and it would have infected relatively few Africans early in its spread, they said.

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On the Net:

Nature: http://www.nature.com/nature