The story of ‘How we know where HIV-1 came from’ is really cool– A group of researchers went into the jungles of Africa, collected lots of monkey poop, and figured out pretty much the exact colony of chimpanzees that transmitted their SIV into humans, which lead to the HIV epidemic we know today.
Those researchers have struck brown gold again!
There are lots of different kinds of ‘HIV’. Apparently, all of the HIV-1 (Group M is causing the HIV epidemic in humans, and then Group N and O) we know today came from chimpanzees that live in the same West-Central region of Africa (these same chimpanzees also infected gorillas).
But this isnt the only place chimpanzees live.
Why did HIV-1 originate from these chimpanzees in this part of Africa? It could be that chimpanzees in other parts of Africa are not infected with their version of SIV, or at least, at the same rates as the chimpanzees in West-Central Africa.
To help answer this question, these researchers went to Eastern Africa and collected even MORE monkey poop– from chimpanzees and bonobos. 3108 samples of monkey poop.
After doing genetic analysis on the poop to make sure they werent sampling from the same monkey pooping 3000 times, but lots of different monkeys, they then tested the samples for evidence of SIV infection (presence of SIV proteins, genome, or antibodies to SIV).
The infection rates were as high as 30% in some locations, but on average, were at about 13%. This is pretty much exactly what they found when looking at chimpanzees in West-Central Africa.
So why the heck did humans get HIV from the West-Central chimpanzees, on several occasions, and not the Eastern chimpanzees, ever??
It might have something to do with differences in the viruses infected the Western vs Eastern chimpanzees.
The scientists did a genetic analysis of the SIV they found in the Eastern chimpanzees and determined that the virus would need to make more changes in gag and vpu to replicate well in humans than the West-Central virus had to make.
The hurdle to go from chimpanzee–>human is not only about the differences between chimpanzees and humans, but also about the genetics of the viruses in the chimpanzees. Here is a fantastic bit from the paper– those of you who have followed the Vpu saga from the beginning will love this:
It has been shown that upon cross-species transmission, the ape precursors of HIV-1 had to switch from Nef- to Vpu-mediated tetherin antagonism (36, 61). However, only the pandemic M group viruses acquired efficient antitetherin activity, while the much-less-prevalent group N, O, and P viruses either failed to gain this activity or lost other Vpu functions (36, 61, 62, 81, 85, 86). These findings have been taken to indicate that successful SIV zoonoses require effective tetherin antagonism (23). When we compared ape virus Vpu sequences to that of the HIV-1 group M consensus, we found that some SIVcpzPtt Vpu proteins required only very few changes to gain key functional motifs (Fig. 8). In contrast, most SIVcpzPts Vpu proteins required a substantially larger number of substitutions to acquire these same human-specific signatures (Fig. 8).
All of this really cool new information that helps us learn why HIV happened– all of this info we got from monkey poop.