-- 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.
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
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
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
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
"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."