Lentiviruses, we think, are evolutionarily young.
For example– you have retroviruses in your DNA (ERVs) from other
genuses (genii?) genera of retrovirus that are millions and millions of years old. So we know those other genuses (genii?) genera are millions and millions of years old.
Lentiviruses, on the other hand, havent left us many of these kinds of fossils for us to figure out their age. We can still put out a good estimate, though. For instance– SIV is all over the place in non-human primates in Africa. And while its ubiquitious in Africa (implying ‘old’), its not found in non-human primates in Asia, or New World monkeys. It almost certainly wasnt around when the common ancestors of all these organisms were cohabitating. So, SIV is old, but not that old, evolutionarily. Previous estimates put SIV into chimpanzees in between 1266-1685.
Yeahhh… Looks like that number has been pushed back, for chimpanzees, about *squints at phylogenetic tree* 23,000 years. O.o
This group of scientists looked for SIV in primates that had been separated from the African mainland for ~10,000 years. When they used those new sequences to recalibrate SIVs molecular clock, things got pushed back. Waaaaay back. SIV could be 32,821-132,780 (best estimate 76,794) years old.
SIV is, for the most part, non-pathogenic in African primates. Animals that can survive infection until reproductive age have been selected for, as well as variants of the virus that are less pathogenic (they reproduce and spread just fine, but they dont kill you ASAP). Countless primates had to die for this to happen. Darwinian medicine.
So it annoys me when, in a Science paper, they say something like this:
Although evidence of codivergence between SIV and its natural hosts is still lacking, our results are suggestive that generally low pathogenicity of SIV is likely a consequence of long-term host- virus coevolution. A similar accommodation between HIV and humans should therefore not be expected to arise soon.
Um, no, it should not be expected to arise ever, in humans. I mean, freak chance it could happen, but it wont happen for the same reasons it happened in non-human primates. Modern humans find Darwinian medicine unethical.
We do not say “Oh? You have HIV-1? Lets see what happens!” We give people antiretrovirals to prevent horizontal transmission and to ‘artificially’ extend the lives of HIV+ individuals. We give pregnant mothers antiretrovirals to prevent vertical transmission, thus even if Mom had The Good Genetics and was infected with The Good Virus, she would not pass it on to her offspring (who presumably would also have aspects of The Good Genetics).
Im not anticipating the evolutionary truce that African non-human primates have with their SIVs in humans at any point in the future. But this is still cool paleovirology 🙂