Hot Zone Question

[Biology Department]

In article <deirdre at deeny.MV.COM> _Deirdre writes:
What fascinates me is the thesis that this may be a disease naturally
hosted in big game (e.g. leopards or elephants) and that, because numbers
of the natural host are dwindling, it's jumping species to something more
available.

	Perhaps I am missing something, but why should a virus jump into a new  
host just because its current host numbers are 
dwindling?  
I do not see a clear link between a _decrease_ in host 
population and an increase in ability for horizontal viral transmission.  To 
me, a decreased viral population (due to a decreased host number) would 
reduce the chance for a virus to jump into a new host.  My basic 
confusion is that I do not understand how a dwindling host number could 
enhance viral mutation rates because mutations are the mechanism by which 
mutated viruses are generated.  It seems that a  larger
population of viral carriers would yield a larger population of viruses, 
thus the chance for favorable-random mutations is increased when the host 
population is increased.  The latter analysis is contrary to the statement 
above--i was just wondering how decrease in host population could 
enhance host transfer.

Jeff Huckaby
Molecular Biology
William Jewell College
Liberty, MO 64068
USA
eMail mowjmat at coop.crn.org