A genetic analysis of thousands of individual viruses has confirmed beyond reasonable doubt that HIV first emerged in Kinshasa, the capital of the Belgian Congo, in about 1920 from where it spread thanks to the colonial railway network to other parts of central Africa.
Scientists have nailed the origin of the Aids pandemic to a colonial-era city — then called Leopoldville which was then the biggest urban centre in Central Africa including a market in wild "bush meat" captured from the nearby forests.
A "perfect storm" of factors then led to the virus' spread in the human population.
UNAIDS estimates that 35 million people were living with HIV in the world at the end of 2013.
Scientists from University of Oxford said, "Thirty years after the discovery of HIV-1, the early transmission, dissemination and establishment of the virus in human populations remain unclear. Using statistical approaches applied to HIV-1 sequence data from central Africa, we show that from the 1920s Kinshasa (in what is now the Democratic Republic of Congo) was the focus of early transmission and the source of pre-1960 pandemic viruses elsewhere. Location and dating estimates were validated using the earliest HIV-1 archival sample, also from Kinshasa. Our results reconstruct the early dynamics of HIV-1 and emphasize the role of social changes and transport networks in the establishment of this virus in human populations."
Vendors sell their products beside a railroad track in Kinshasa, Zaire (File photo via Getty Images)
The breakthrough was possible due to a new, sophisticated analysis of hundreds of genetic sequences of HIV from different time points and locations.
The researchers also note that 13 documented cases exist of different simian viruses jumping from chimpanzees, gorillas and monkeys into humans, but only one — known has HIV-1 group M — sparked a global epidemic. They show that group M and another strain, group O, expanded at the same rate until about 1960, but then group M nearly tripled its rate of spread. Possible reasons include public health campaigns that had contaminated needles and an increase in the number of clients of sex workers.
"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. "This means we can say with a high degree of certainty where and when the HIV pandemic originated."
"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.
"Data from colonial archives tells us that by the end of the 1940s over one million people were travelling through Kinshasa on the railways each year. Our genetic data tells us that HIV very quickly spread across Congo, a country the size of Western Europe," Dr Faria said.
"Our research suggests that following the original animal-to-human transmission of the virus, probably through the hunting or handling of bush meat, there was only a small window during the Belgian colonial era for this particular strain of HIV to emerge and spread into a pandemic," Professor Pybus said.
"By the 1960s, transport systems such as the railways that enabled the virus to spread vast distances were less active, but by that time the seeds of the pandemic were already sown across Africa and beyond," he said.
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