HIV Outbreak Began Decades Earlier Than Thought

WEDNESDAY Oct. 1, 2008 -- The most pervasive global strain of HIV began spreading in humans around 1900 in sub-Saharan Africa, a new study claims.

The research, which is published in the current issue of Nature, found that HIV began spreading between 1884 and 1924, around the same time urban centers in west central Africa were established. This estimated time of origin is decades earlier than the previous estimate of 1930.

For the study, researchers analyzed tissue samples and uncovered the second-oldest genetic sequence of HIV-1 group M. They used this and other HIV-1 genetic sequences to construct a family tree of the origin of the viral strain and to estimate the time of origin of HIV-1 group M.

The researchers worked with a 1960 sample of HIV gene fragments from a wax-embedded lymph-node tissue biopsy from a woman in Kinshasa in the Democratic Republic of the Congo. This 1960 virus is the second-oldest known HIV-1 group M genetic sequence, with the oldest being a 1959 blood sample from a man also from Kinshasa.

"Previous work on HIV sequencing had been done on frozen samples, and there are only so many of those samples available," lead researcher Michael Worobey, an assistant professor of ecology and evolutionary biology at the University of Arizona in Tucson, said in a university news release.

"From that point on, the next oldest sequences that anyone has recovered are from the late 1970s and 1980s, the era when we knew about AIDS. Now, for the first time, we have been able to compare two relatively ancient HIV strains. That helped us to calibrate how quickly the virus evolved and make some really robust inferences about when it crossed into humans, how quickly the epidemic grew from that time and what factors allowed the virus to enter and become a successful human pathogen," said Worobey.

Previous studies have shown that HIV spread from chimpanzees to humans in southeastern Cameroon.

Worobey said that the HIV epidemic that resulted from the turn-of-the-century spread correlates to the urbanization of colonial Africa, principally the present-day city of Kinshasa in the Democratic Republic of the Congo.

The growth of cities and associated high-risk behaviors may have been a principal cause of the rapid spread of the virus.

Worobey is optimistic about the eventual extinction of the HIV virus.

"I think the picture that has emerged here, where changes the human population experienced may have opened the door to the spread of HIV, is a good reminder that we can make changes now that could help reverse the epidemic. If HIV has one weak spot, it is that it is a relatively poorly transmitted virus. From better testing and prevention, to wider use of the antiretroviral drug therapy, there are a number of ways to reduce transmission and force this virus back into extinction," he said.

More information

The U.S. Centers for Disease Control and Prevention have more about HIV.

Posted: October 2008


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