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Colonial link to HIV epidemic

6th October 2008

The spread of HIV/AIDS has been linked in new research to the growth of large cities in African countries at the height of the colonial era.

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Researchers in the United States say the virus is older than was previously thought, and that it probably began to spread in its current form in the last quarter of the 19th century, as fast-growing African cities brought more and more people together.

Scientists at the University of Arizona say that major colonial cities began their expansion between 1884 and the turn of the 20th century. High concentrations of people in urban areas led to high-risk sexual behaviour, boosting the spread of the virus as a human pathogen.

Previous estimates had put the start of HIV's spread among humans in around the 1930s.

Team leader and Tucson-based evolutionary biology professor Michael Worobey spent many years studying how to recover the fragmented pieces of viral DNA and RNA from archival specimens, to track when the virus first jumped from chimpanzees to humans.

His team has tracked the earliest known recorded specimen of HIV-1 group M genetic sequence back to blood samples taken from a man and a woman in Kinshasa, the current capital of the Democratic Republic of Congo, in 1959.

They found the man and woman had a common ancestor dating back to around 1900.

The two samples are the oldest links to the history of the HIV epidemic, making the strains of HIV they carry relatively ancient.

Previous work on HIV sequencing had been done on frozen samples and there are only so many of those samples available.

Later samples date from the late 1970s and 1980s, when AIDS was already entering into public awareness in the Western world.

The Kinshasa samples helped the researchers to calibrate how quickly the virus evolved.

Worobey said they had made some 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.

While the virus was originally transmitted between monkeys and humans in southeastern Cameroon, it was then spread rapidly by the growth of urban centres developed by the colonial powers of the time in the surrounding countries of Central African Republic, Congo, Gabon and Equatorial Guinea.

But the research does not just give a clearer picture of HIV's epidemiological history, however.

Worobey said he also saw hope for the future.

If changes made by the human population had boosted the spread of HIV in the first place, then it stood to reason that further changes made by humans could reverse the epidemic.

He said HIV was a relatively poorly transmitted virus, citing a number of ways to reduce transmission and force it back into extinction.

They included better testing and prevention and wider use of antiretroviral drug therapy, giving plenty of reasons for optimism.

 

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