HIV-1 Adaptation to host/various musings

Ian A. York york at
Wed Oct 18 09:01:48 EST 1995

In article <4629pj$h07 at>,
Jeffrey Rice <jrice at> wrote:
>	Since the viruses adapt to their hosts via mutation, selection, 
>ect., why would HIV-1 become more lethal across generations?  I guess I am 
>making the assumption it originated with something like SIV, which causes 
>symptoms more like HIV-2.  Wouldn't natural selection favor a less virulent 
>strain, to prolong host life and therefore transmission opportunities?  Or 

This has been discussed in great detail on bionet.virology.  The bottom
line is that the generalization that viruses and other pathogens adapt to
their hosts and become less virulent over time is a myth.  There are some
apaprent examples of this happening, but there are many examples where it
deosn't happen and some where the reverse may be happening.  My favourite
counterexample is the most lethal virus known*, with a mortality rate of
well over 99.99999%, rabies virus: this has been around for thousands of
years at the least without any signs of attenuating. 

*It's too early to be sure about HIV, but that may have a similar 

Ian York   (york at
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-3921     Fax  (617)-632-2627

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