New research has found that the HIV epidemic first broke out in Kinashasa, now capital of the Democratic Republic of Congo, as early as the 1920s. The analysis confirmed suspicions, though also ruled out less popular theories about the virus’ origins.

An international team of researchers including academics from Oxford reconstructed the genetic history of the HIV-1 group M pandemic, managing to find the common ancestor of group M and trace its history.  Although strains HIV have jumped from primates and apes to humans at least 13 times in history, only one transmission eventually resulted in a global pandemic.

“Until now most studies have taken a piecemeal approach to HIV’s genetic history, looking at particular HIV genomes in particular locations,” explained Professor Oliver Pybus, an Oxford academic and a senior author of the paper. “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. This means we can say with a high degree of certainty where and when the HIV pandemic originated.”

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The study estimates that the first human to get HIV, probably a hunter coming into contact with a chimp blood, was infected around 1920, with 95 percent of the estimated dates falling in the period between 1909 and 1930.

The research also showed the HIV was able to spread due to a combination of factors in the region. The railway lines in particular helped bring the virus to large cities such as Kinashasa, the largest city in the region, which had over a million annual rail passengers by the 1940s.

Nuno Rodrigues Faria, a researcher at Oxford University and another author on the paper, added that “alongside transport, social changes such as the changing behaviour of sex workers, and public health initiatives against other diseases that led to the unsafe use of needles may have contributed to turning HIV into a full-blown epidemic.”

After spreading in Africa the virus later travelled across the world. It was first noticed by US doctors in 1981 though is believed to have arrived earlier, and has since infected 75 million people worldwide and killed almost 40 million.

The research into HIV’s historical origins may prove be useful to prevent future infections.  Rodrigues Faria concluded that the “knowledge of the circumstances that facilitated the epidemic expansion can assist the development of effective education and prevention programs.”