The HIV pandemic originated in Kinshasa, the capital of the Democratic Republic of Congo, some 90 years ago, scientists said Thursday, appearing to resolve the longstanding mystery of one of humanity's most persistent diseases. The research, published in the journal Science, traces the genetic roots of the human immunodeficiency virus, a precursor to AIDS, to the Central African country.

What the research doesn't resolve is the delicate question about how the virus was transferred from primates or non-human apes to humans. But the researchers, mainly from Oxford, point out in a press release that it was "probably through the hunting or handling of bush meat." Yet the paper seems to lay to rest work suggesting that HIV originated in West Africa.

"Until now most studies have taken a piecemeal approach to HIV's genetic history, looking at particular HIV genomes in particular locations," said senior author Oliver Pybus of Oxford University's Department of Zoology, in a statement. "It seems a combination of factors in Kinshasa in the early 20th Century created a 'perfect storm' for the emergence of HIV, leading to a generalized epidemic with unstoppable momentum that unrolled across sub-Saharan Africa."

Part of that perfect storm was the country's railway system, a web with Kinshasa at the center, through which about one million people were traveling at the end of the 1940s. Toss in unsafe health care, which treated people for other illnesses with HIV-infected needles, and the sex trade, and the Democratic Republic of Congo was a sure source of pandemic. By the 1970s, health workers discovered AIDS in the United States.

HIV traveled by rail and water "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," Pybus said. They concluded that the spread to these cities gave it "secondary foci" from which it headed to the rest of Africa. "We think it is likely that the social changes around the independence in 1960 saw the virus 'break out' from small groups of infected people to infect the wider population and eventually the world."

Source: O. Pybus, et al. The early spread and epidemic ignition of HIV-1 in human populations Science. 2014.