A new study has traced the origins of HIV back to the early 20th century in the western region of Congo. From there, scientists say that the deadly virus spread throughout Africa over the next several decades and eventually turned into a worldwide epidemic, infecting 75 million people.

According to the Times of India, scientists have proved beyond reasonable doubt that HIV first appeared in Kinshasa, the capital of what is now known as the Democratic Republic of the Congo, around 1920. It then spread to other parts of central Africa through the emergence of social factors, including railroad expansion, sex workers and unsafe medical practices.

Scientists say that the origin of the epidemic of AIDS spread from the region, which was then called Leopoldville, to the biggest urban center in Central Africa.

"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," Nuno Faria of Oxford University 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," reported scientists from the University of Oxford, reports the Times of India.

The authors of the study also note that the global pandemic was ignited after the HIV-1 group M virus jumped from chimpanzees, gorillas and monkeys into humans.

"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."

However, according to William Schneider, a professor who studies the history of medicine at Indiana University-Purdue University Indianapolis, the theories about the spread of the disease aren't convincing because they're based on questionable information from a time when Europeans controlled much of Africa.

"Colonial records are well-known by historians and anthropologists to be biased, selective and above all in need of broader understanding of historical and cultural circumstances to evaluate their usefulness," he said, reports Health24.com.