The deadly virus responsible for the global HIV/AIDS pandemic emerged around 1920 in the city of Kinshasa, the capital of the Democratic Republic of the Congo, according to new research that has relevance to the effort to understand how another deadly virus, Ebola, reestablished itself in West Africa.
The study, published in the journal Science, reveals that the HIV virus was already established and spreading in Africa long before the U.S. Centers for Disease Control and Prevention first took note of it. The CDC's first record of the illness occurred on June 5, 1981, when an unusual type of "pneumonia" was detected in five homosexual men from Los Angeles.
No one then knew that the deadly strain of the virus, which has since killed an estimated 39 million people, had already taken hold in the Congo some 60 years earlier.
"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," co-author Oliver Pybus, an Oxford University zoologist, said.
Lead author Nuno Faria, also from Oxford University's Department of Zoology, explained that "by the end of the 1940's, over one million people were traveling through Kinshasa on the railways each year." At the time, what is now the Democratic Republic of the Congo was under Belgian colonial rule and experiencing steady urban growth Faria and his team examined the genetics of 348 "HIV-1 group M" samples from the former Belgian Congo, and 466 additional samples from nearby regions. This particular viral strain, "M," has proven to be the deadliest in humans, but virologist Beatrice Hahn of the University of Pennsylvania explained to Discovery News that it represents just one of several different instances where the illness jumped from a non-human primate to people -- likely by the consumption or handling of bushmeat.
The researchers next compared the relatedness of the HIV genetic sequences to create phylogenies, or family trees. The scientists then calculated the rate at which the virus mutates to date the origin of each "branch" on the trees.
This reconstruction of the genetic history of HIV-1 group M revealed both the date and location of the epidemic's origins, placing Kinshasa at ground zero.
Prior research suggests that one or more people first contracted the virus from an infected chimpanzee in southeastern Cameroon. The new study holds that the individual(s) traveled to Kinshasa, where the virus became established in humans and spread.