For years, researchers have tried to pinpoint the origins of the HIV pandemic that is responsible for around 36 million deaths worldwide. Now, an international research team says they have found the answer; it began in Kinshasa - what is now the capital of the Democratic Republic of Congo - in the 1920s.
The research team, led by investigators from the University of Oxford in the UK and the University of Leuven (KU Leuven) in Belgium, publish their findings in the journal Science.
HIV (human immunodeficiency virus) was first described more than 30 years ago. To date, almost 75 million people around the globe have been infected with the virus. Sub-Saharan Africa is the most severely affected, with almost 1 in 20 adults infected with HIV.
According to the researchers, it is well established that HIV has been transmitted from primates and apes to humans at least 13 times.
They note, however, that only one of these transmissions - involving the strain HIV-1 group M - led to the pandemic we know today. But where and when did this pandemic begin?
Senior author Prof. Oliver Pybus, of the Department of Zoology at the University of Oxford, says that the majority of HIV studies have used a "piecemeal approach" to determine the genetic history of HIV, analyzing specific HIV genomes from certain locations. But he and his colleagues decided to take a different approach.
"For the first time we have analyzed all the available evidence using the latest phylogeographic techniques, which enable us to statistically estimate where a virus comes from," Prof. Pybus explains. "This means we can say with a high degree of certainty where and when the HIV pandemic originated."
Using these techniques, the team traced the origins of the HIV pandemic back to Kinshasa - formerly known as Léopoldville - in the 1920s. Located on the Congo River, Kinshasa is now the largest city and the capital of the Democratic Republic of Congo (DRC).
Prof. Pybus says they then identified a number of factors that created a "perfect storm" for HIV to spread from Kinshasa to Sub-Saharan Africa between the 1920s and 1950s.
"Once the pandemic's spatiotemporal origins were clear, they could be compared with historical data and it became evident that the early spread of HIV-1 from Kinshasa to other population centers followed predictable patterns," says senior author Prof. Phillippe Lemey, of the Raga Institute at the University of Leuven.
Transport and social changes likely to have led to HIV pandemic
The transport links from Kinshasa to central Africa - particularly the railways - are likely to have been a major contributor to the spread of HIV, the researchers say, noting that more than 1 million people were using Kinshasa's railways annually toward the end of the 1940s.
"Our genetic data tells us that HIV very quickly spread across the DRC, traveling with people along railways and waterways to reach Mbuji-Mayi and Lubumbashi in the extreme South and Kisangani in the far North by the end of the 1930s and early 1950s," explains first author Dr. Nuno Faria, of the Department of Zoology at the University of Oxford. "This helped establishing early secondary foci of HIV-1 transmission in regions that were well connected to southern and eastern African countries."
The researchers note that social changes surrounding independence in the 1960s likely led to the spread of infection from small populations to larger populations, eventually leading to a worldwide pandemic.
They point out that there were a high number of sex workers in the 1960s as well as public health campaigns against other diseases that led to the unsafe use of contaminated needles - both factors that could have led to the dramatic spread of HIV.
Prof. Pybus adds:
"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.
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."
The team says further research is warranted to determine other social factors that may have contributed to the HIV pandemic.
Medical News Today recently reported on a paper in The Lancet revealing that HIV has rebounded in a second baby believed to have been cured of the virus with early antiretroviral therapy.