The HIV pandemic that has plagued us for decades almost certainly began in Kinshasa, the capital of the Democratic Republic of the Congo (DRC).

Scientists from Oxford University and University of Leuven, reconstructed the genetic history of the HIV-1 group M pandemic, and concluded that its roots started in Kinshasa, DRC around 1920.

HIV can spread from one person to another through bodily fluids, including blood, semen, rectal and vaginal fluids, and breast milk. Transmission occurs when these fluids come into contact with a mucus membrane or damaged tissue, as well as directly into the bloodstream through a needle.

It’s been well documented that HIV transmission from primates to humans has occurred at least 13 times, but only one of these transmissions sparked a human pandemic. To date, nearly 75 million infections have been reported.

The researchers suggest that a blend of factors, such as urban growth, improvement in transportation systems, and changes to the sex trade that took place between the 1920s and 1950s helped the disease spread from Kinshasa to all other parts of the world.

“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,” said Pybus in a statement.

The scientists say that further research is required to understand how specific social factors contributed to the roots of the HIV pandemic. Specifically, research on archival specimens is needed to analyze the evolution of HIV, as well as how the virus is related to the spread of Hepatitis C and the use of tainted needles to help provide additional insight into the factors that helped to spread HIV across the globe.