Here are some things you might not know. Different versions of the virus almost certainly hopped from chimpanzees, where it’s known as simian immunodeficiency virus, to humans several times in southern Cameroon and elsewhere in the Congo River basin. It first spread in humans in the 1920s in what was then called Belgian Congo, today’s Democratic Republic of Congo, or DRC. And it was likely transportation networks combined with changing medical practices and social conditions that took main-group HIV strains, or HIV-1 M, from an outbreak to a global pandemic, while others remain confined largely to central Africa.
It’s likely that unsterilized injections in sexually transmitted disease clinics in the 1950s combined with an increase in the number of sex workers’ clients in the early 1960s helped spread group M throughout DRC and Africa.
“We suggest a number of factors contributed to a ‘perfect storm’ for HIV emergence from Kinshasa and successful epidemic and eventually pandemic spread,” Phillippe Lenney, co-author of a new study on the earliest origins of the HIV crisis, says in an email. Those factors include urban growth, the development of new transportation infrastructure, and changes in commercial sex work after the DRC’s independence from Belgium.
To reach that conclusion, the team first had to sort out where and when HIV originated and how different groups of the virus spread over time. While researchers were confident humans had contracted HIV by around the 1930s, hypotheses about where it came from were based largely on circumstantial evidence, such as HIV's high genetic diversity in DRC, Cameroon, Gabon, and the neighboring Republic of Congo. Using a large database of HIV samples from central Africa and a statistical method called phylogeography, which used samples of different strains of HIV as well as when and where they were collected to reconstruct the disease’s genetic and geographic history, the researchers put HIV-1 M’s origins in Kinshasa, Democratic Republic of Congo, in about 1920. From there, the disease spread first by train and later by river to cities throughout DRC as well as the Republic of Congo, including Pointe-Noire and Brazzaville, just across the Congo River from Kinshasa.
That left open questions about why HIV-1 M and not others, such as the “outlier” group HIV-1 O, managed to spread throughout Africa and the world. Both M and O groups, the team found, spread at about the same rate until 1960, at which point group M expansion exploded. It’s likely, the authors argue, that unsterilized injections in sexually transmitted disease clinics in the 1950s combined with an increase in the number of sex workers’ clients in the early 1960s helped spread group M throughout DRC and Africa. The prevalence of Haitian professionals in Kinshasa around that time lends support to the idea that this group spread the disease to the Americas, they write.
Unfortunately, that's not great news for the future. The range of factors involved “makes it difficult to make the connection to particular intervention policies at present,” since those are specific to the particular disease and outbreak, Lenney says.