HIV-1 Adaptation to host/various musings

Jeffrey Rice jrice at pomona.edu
Tue Oct 17 23:05:27 EST 1995


	I was reading Robin Henig's _A Dancing Matrix_, and came across a 
couple ideas that didn't seem to work.  (BTW- has anyone else read this 
book?  I'm loving it...)
	Dr. Henig says that HIV-1 shows signs that it may have existed in a 
human host for several generations, as opposed to HIV-2 which shows signs of 
a recent cross-over.  He bases this on comparisons to SIV, as well as case 
studies dating to the 50's, as well as historical suggestions.
	HIV-1 is also more lethal than HIV-2, in that I guess most patients 
infected with HIV-2 can be unaffected for two decades or more.
	Here's my thought/question:
	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 
can we guess from this that HIV-1 was MORE virulent historically than it is 
now?
	What got me started on this topic was the (correct) idea that the 
intention of a virus is not cell death, but replication.  If that includes 
cell death of the host, this can be acceptable, assuming enough replication 
is a result and transmission to a new host is possible.  Host death kills 
the parasite, usually.  (Obviously we see with viruses like Ebola, ect. that 
much transmission occurs after death, since the victims have bled-out.  This 
seems a less secure method to me, though...)
	Anyway, I'd be interested to hear people's thoughts on this.  If you 
are interested in immunology or virology, I'd recommend Henig's book.  It 
really is facinating, not only in its coverage of the emergence of HIV but 
also in other viruses.
					Jeff Rice



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