A new study published in Science has traced the origins of the HIV-1 group M pandemic to 1920s Kinshasa, in what is now the Democratic Republic of the Congo. While strains of HIV are known to have crossed from other primates to humans on a number of occasions, only this particular outbreak has led to a pandemic. Scientists have long wanted to know why this particular strain was able to spread so successfully, when others had petered out. An international team lead by scientists from Oxford University and the University of Leuven reconstructed and examined the genetic history of the virus. This led them to conclude that a “perfect storm” of social factors allowed the virus to break out of Kinshasa in the 1920s and spread around the world.

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The virus is believed to have jumped species through people hunting primatesand handling bush meat. In fact, this is believed to have happened on at least 13 occasions. What set the Kinshasa incident apart from other transmissions was the city’s size and rapid urban growth, the heavily used railway network during Belgian colonial rule, and a flourishing sex trade in a city with a high proportion of men. There was also a very active water transport system. Kinshasa was a hub for the country’s railway network, and by the late 1940s an estimated one million people passed through the city using the rail network each year. This led to the virus being spread to other cities such as Mbuji-Mayi and Lubumbashi in the south of the country, and to Kisangani in the north by the end of the 1930s. These cities in turn were well connected to neighboring countries and the virus began to take off.

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In 1960, the DRC gained independence from Belgium. While from then on the rail system began to play a less important role in the country, the virus was already in the population. The “changing behavior” of sex workers and the use of unsterilized needles in public health initiatives combating other diseases are believed to be contributing factors to the virus then developing into a “full-blown epidemic” regionally. Study co-author Nuno Faria told Reuters: “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.”

Co-lead author of the study Professor Oliver Pybus of Oxford University says: “Until now most studies have taken a piecemeal approach to HIV’s genetic history, looking at particular HIV genomes in particular locations. 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. 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 generalised epidemic with unstoppable momentum that unrolled across sub-Saharan Africa.” Today an estimated 35 million people worldwide are living with HIV. It is estimated 40 million people have died in the pandemic.

Via Science Daily and Reuters

Photos by CDC/C. Goldsmith via Wikimedia Commons; Jon Rawlinson via Flickr