Tom,
You raise some interesting points regarding mutations, but you need to
remember that the number of ways an organism can change via mutations
or other mechanisms is not unlimited. Consider, for example,
mutations in gp120. Random mutations in this protein must retain the
ability to bind to cellular receptors, while avoiding the immune
response. There are only a finite number of ways that this may be
acheived. This is why you see very few mutations in other proteins,
such as p24. It seems that there are very few ways to construct a
viral capsid.
For a virus to change the way it is transmitted, then, is not a simple
matter. Do you know of any virus which was transmitted by one route,
and then has change to an entirely different one?
The concern about HIV switching from a sexual route to a respiratory
or vector route makes for good chit chat, but is completely without
precedent as far as I know. Even for a rapdily mutating virus, the
constraints imposed during replication in the human host have not
translated into any evidence suggesting that the virus is
fundamentaly changing it's biology.
Keep warm up on that iceburg, Tom. Maybe some day we can rescue you.
Jay Mone'
