The City Where HIV First Infected a Human

It is easy to see why AIDS seemed so mysterious and frightening when US medics first encountered it 35 years ago. The condition robbed young, healthy people of their strong immune system, leaving them weak and vulnerable. And it seemed to come out of nowhere.

Today we know much more how and why HIV – the virus that leads to AIDS – has become a global pandemic. Unsurprisingly, sex workers unwittingly played a part. But no less important were the roles of trade, the collapse of colonialism, and 20th Century sociopolitical reform.

HIV did not really appear out of nowhere, of course. It probably began as a virus affecting monkeys and apes in west central Africa.

From there it jumped species into humans on several occasions, perhaps because people ate infected bushmeat.Some people carry a version of HIV closely related to that seen in sooty mangabey monkeys, for instance. But HIV that came from monkeys has not become a global problem.

We are more closely related to apes, like gorillas and chimpanzees, than we are to monkeys. But even when HIV has passed into human populations from these apes, it has not necessarily turned into a widespread health issue.

HIV originating from apes typically belongs to a type of virus called HIV-1. One is called HIV-1 group O, and human cases are largely confined to west Africa.

In fact, only one form of HIV has spread far and wide after jumping to humans. This version, which probably originated from chimpanzees, is called HIV-1 group M (for “major”). More than 90% of HIV infections belong in group M. Which raises an obvious question: what’s so special about HIV-1 group M?

A study published in 2014 suggests a surprising answer: there might be nothing particularly special about group M.

It is not especially infectious, as you might expect. Instead, it seems that this form of HIV simply took advantage of events. “Ecological rather than evolutionary factors drove its rapid spread,” says Nuno Faria at the University of Oxford in the UK.

Faria and his colleagues built a family tree of HIV, by looking at a diverse array of HIV genomes collected from about 800 infected people from central Africa.

Know more about it @ http://www.bbc.com/earth/story/20151119-we-know-the-city-where-hiv-first-infected-a-human