HIV-1 Adaptation to host/various musings

A.J.Cann nna at
Fri Oct 20 06:52:58 EST 1995

york at (Ian A. York) wrote:
>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. 

Have to comment on this. The key phrases here are "adapt to their hosts" & 
"mortality rate of well over 99.99999%" (do you mean 100% - not true; 
99.9% would be more accurate). Snag is that humans are not the natural 
host of rabies virus - they are dead end hosts who do not play a 
significant part in the transmission of the virus over "thousands of 
years". Hence each human infection is essentially a new event & the virus 
does not have chance to "adapt to it's host" in evolutionary terms.

Dr Alan J. Cann  PhD,   Department of Microbiology & Immunology,
University of Leicester,  P.O. Box 138,  Medical Sciences Building,
University Road, Leicester LE1 9HN,  UK.
Email: nna at

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