David Brill (aka David Wise)
December 1 is World Aids Day. To mark the event medical journalist David Wise looks at the humble origins of this global killer and its journey from an isolated outbreak to a worldwide pandemic.
Léopoldville may not be a familiar name to many, yet the city played host to one of the defining events of mankind’s recent history. The former Belgian colonial capital – now known as Kinshasa, Democratic Republic of the Congo – is thought to be the birthplace of HIV, the virus responsible for the AIDS pandemic which is currently affecting over 33 million people worldwide.
The precise origins of HIV remain a mystery but new research allows scientists to paint a more detailed picture than ever before. They now believe that the virus first reached humans in Léopoldville around 100 years ago, where it found a foothold among the booming population of the newly-founded city.
It is likely that HIV spread slowly at first, experts say, while the fact that symptoms differ widely between individuals may have prevented it from being recognized for many years. It was not until 1981 that French scientists Françoise Barré-Sinoussi and Luc Montagnier formally identified the virus – a discovery that was honored this year with the award of the Nobel Prize for medicine.
The true beginning of the story, however, begins not with humans but with our primate cousins. Today there are several different types of HIV, each of which may have its own tale to tell, but the particular strain responsible for the current pandemic seems to have evolved from a virus which naturally infects chimpanzees. In 2006 researchers announced that they had found this HIV forefather – the Simian Immunodeficiency Virus (SIV) – among wild chimps living in southeast Cameroon.
Most scientists accept that SIV became HIV, but how it first crossed the species barrier is largely a matter for speculation, according to Professor Robin Weiss, an HIV expert from University College London, UK.
“The most likely explanation is that it began with the butchering of apes,” he explains. “There was blood and splintered bones and goodness knows what lying around, and then the virus got transferred into small cuts or abrasions on the skin. If you wanted to be lurid you could raise a King Kong scenario of sex with a great ape but I think that’s a bit sensational myself.”
The first known case of HIV comes from a preserved tissue specimen dating back to 1959, which was found in the archives at the University of Kinshasa. In 2000, Betty Korber and her team at the Los Alamos National Laboratory, US, published an important research paper analyzing the genetic sequence of this virus. Their calculations, they said, suggested that the virus had likely been born around 1931 – back when Kinshasa was still known as Léopoldville.
But this information begged an important question which has only recently been answered: how did the slaughtering of chimps in southeastern Cameroon lead to the infection of humans in Léopoldville some 700km away?
The answer was provided in October of this year when Michael Worobey and his colleagues from the University of Arizona, writing in the journal Nature, announced that they had found another early HIV specimen lurking in the archives at Kinshasa. The tissue sample – a lymph node taken from an adult woman – had been fixed in preservative back in 1960.
This discovery enabled the team to compare the virus with Korber’s specimen from 1959. By looking at genetic differences between the two samples and tracing their family trees backwards, they established that the viruses must have shared a common ancestor between 1884 and 1924. Their best estimate puts the birth of HIV at 1908 – some 23 years earlier than previously thought.
Worobey’s team went one step further and placed their genetic studies alongside demographic data on the growth of cities in west-central Africa. They found that their estimate of 1908 coincided with a period of population boom in Léopoldville, suggesting that growth of the city provided the necessary kick-start for HIV to spread. Before 1900, there was not one settlement in the area with more than 10,000 people, but by 1910 Léopoldville had established itself as the region’s major city.
As the colonial outpost grew, so it continued to flourish as an administrative and trading center. With transportation at the time largely restricted to boats, Léopoldville found itself ideally situated on the Congo River – the final destination of many of the tributaries that run through the forests of Cameroon. The identity of the person that first contracted SIV may remain a mystery, but their arrival in the city now seems the likely trigger for the modern-day AIDS pandemic.
This newfound understanding of where HIV came from can provide important insights into the evolution of future pandemics, according to Weiss.
“These examples of particular viruses help to inform our general thinking about the origins of infections that come from animals. And for sure we’ve haven’t seen the last one – there’ll be some other disease like SARS or something that we haven’t even thought about today,” he says.
“And looking back at HIV in its very humble, small beginnings… who would have guessed that this would turn out to be the major killer at the end of the 20th century?”
