HIV - how it crossed over to humans

Over at Aetiology, Tara has #16 in her series "Emerging Disease and Zoonoses". This one focuses on HIV - its evolution in Africa and the probable way it was transferred from wild chimps to humans.

It can't be said often enough that "nothing in biology makes sense except in the light of evolution." Moving from physical characteristics--color, bone shape, the form of bacterial cells--to genetic characteristics in order to classify organisms--and infer phylogeneis--was a giant advance. That the molecular characteristics confirmed what was known using physical characteristics was a breakthrough, and allowed for more sophisticated analyses of organisms that don't have bones or other easily-observable physical features that allow for simple classification into groups: microbes. I've previously pointed out the utility of phylogenetic analysis in tracking the spread of pathogens. A new study on the origin and evolution of HIV employs a similar approach in order to elucidate the history of the virus in Africa.

This study has a lot of value for us right now, to, as Tara points out:

A study published in PNAS this time last year showed that cross-species transmission of viruses from primates to bushmeat hunters is an ongoing event. Since it appears SIV transmission into the human population has occurred on multiple occasions (leading to the M, N, and O groups of HIV), we have no reason to think it's not an ongoing process, and that nature may have something worse to offer than HIV. It also, of course, has implications for current surveillance of H5N1. No one knows how many times in history SIVs have entered the human population, only to meet a dead end in the infected human (as H5N1 generally has to date). As this study shows, it only takes one successful transmission event to lead to a pandemic.

Check it out - and add Aetiology to your regular reading, if you haven't already.