HIV/AIDS Emerged as Early as 1880s
for National Geographic News
|October 1, 2008|
The AIDS pandemic in humans originated at least three decades earlier than previously thought, and it may have been triggered by rapid urbanization in west-central Africa during the early 20th century, according to an international team of researchers.
A better understanding of the conditions that helped fuel the pandemic could be key in controlling the disease and preventing future outbreaks of other emerging viruses.
"Rapid urbanization was the turning point that allowed the pandemic to start," said Michael Worobey, an evolutionary biologist at the University of Arizona, Tucson, and lead author of the study.
"We as human beings made some changes that took a virus that could not exist on its own and turned it into a successful epidemic," he added.
Birth of AIDS
Until now it was thought that HIV-1 Group M, the strain of HIV that causes the most infections worldwide, originated in 1930 in Cameroon.
Epidemic levels of AIDS and HIV-1 infections started appearing in Leopoldville, Belgian Congo (now Kinshasa, Democratic Republic of the Congo), around 1960.
Findings from the new study, however, suggest that the virus most likely started circulating among humans in sub-Saharan Africa sometime between 1884 and 1924.
Worobey and his colleagues made the discovery while analyzing tissue samples collected between 1958 and 1960 from Kinshasa. One of them, acquired in 1960, contained bits of HIV-1 RNA, the virus's genetic material.
The researchers compared the 1960 virus with the oldest known HIV-1 strain, which was obtained in 1959 and evolved independently of the 1960 variant. They found that the 1960 version was significantly different.
Next the researchers constructed an evolutionary family tree of the HIV-1 virus, made up of both the 1959 and 1960 strains along with more than a hundred modern viral sequences.
Using a mathematical model, Worobey and his colleagues discovered that the 1960 strain must have been evolving for at least 40 years to account for the number of differences from the 1959 strain.
The model also traced the most recent common ancestor of both strains to 1908.
The team's findings appear today in the journal Nature.
"This confirms that this was a virus that was lurking around for many decades before it exploded into the human population to become a noticeable pandemic, as opposed to something that started in the '70s or '80s," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), in Maryland.
NIAID funded the study along with the National Institutes of Health.
"It solidifies our understanding of the timetable of how this virus emerged from the chimpanzees to establish itself as a human infection," Fauci added.
"[HIV-1] flew below the radar level for decades until social conditions such as the end of colonization, migration of people to cities, increase in prostitution, and promiscuous sexual activity made it much easier for the disease to explode into a pandemic," Fauci explained.
Robert Garry is a microbiologist at New Orleans's Tulane University who was not involved with the study.
In the late 1980s, Garry was the first scientist to examine tissues samples taken from the U.S.'s first confirmed AIDS patient, who died in 1969.
"This study is very important, and what they are finding here is when the human virus started circulating in people," he said. "We still don't know when exactly the virus jumped from chimpanzees to humans, but it may be pushed back even further with this study.
"There will be other emerging viruses in the future, and what we learn about the conditions that help viruses spread, be it social changes or changes within the virus itself, will make us better prepared for other epidemics," he said.
Garry also argues that, though the rapid growth of cities in west-central Africa may have sparked the spread of infections, the virus itself underwent some sort of genetic change to facilitate transmission.
"We have to figure out what that change was," he cautioned.
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