A “perfect storm” of factors that came together in colonial Africa early last century led to the spread of Aids in the human population and eventually a full-blown pandemic infecting more than 75 million people worldwide, a study has found.
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 via the colonial railway network to other parts of central Africa.
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 analysing 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.
“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 the Democratic Republic of Congo, a country the size of Western Europe,” Dr Faria said.
Further social changes brought about as a result of independence in 1960 helped the virus to “break out” from small groups of infected people into the wider population, including immigrant workers from Haiti who then carried their infection back home from where it would eventually be transmitted to visitors from the US.
“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.
Previous studies have suggested that the initial transmission of HIV from chimps to humans probably occurred in the south-east part of Cameroon not far from the border with the Belgian Congo, Dr Faria said.