Science

Scientists believe the findings have finally nailed the origin of the AIDS pandemic to a single source, a colonial-era city then called Leopoldville which had become the biggest urban centre in Central Africa and a bustling focus for trade, including a market in wild "bush meat" captured from the nearby forests.

The study, based on analyzing the subtle genetic differences between various subtypes of HIV, found the human virus had evolved from a simian virus infecting chimps which were hunted for food by people who had probably carried HIV with them into Kinshasa.

Rapid social changes, such as an increase in commercial sex workers and the re-use of dirty syringes, aided the transmission of the virus which was also carried to distant parts of the Congo by the millions of passengers who used the newly-built railway network, the scientists said.

"For the first time we have analysed all the available evidence using the latest phylogeographic techniques, which enable us to statistically estimate where a virus comes from," said Professor Oliver Pybus of Oxford University, a senior author of the study published in the journal Science.

"This means we can say with a high degree of certainty where and when the HIV pandemic originated. It seems a combination of factors in Kinshasa in the early 20 Century created a 'perfect storm' for the emergence of HIV, leading to a generalised epidemic with unstoppable momentum that unrolled across sub-Saharan Africa," Professor Pybus said. Previous research had suggested that HIV was first transmitted from chimps to humans and that the pandemic probably originated in central Africa in the first half of the last century. However, the latest research provides the strongest case for it emerging at a definite time and place – namely Kinshasa in 1920.

"We have managed to integrate spatial information to see where the virus emerged and how it spread to become a full-blown pandemic. Kinshasa at that time was growing fast, it was the biggest city in central Africa at that time and was very well connected to the rest of the Congo," said Nuno Faria of Oxford, another member of the team.