In article <3pnbfp$jte at newsbf02.news.aol.com> stevearenn at aol.com (SteveARenn) writes:
>Do viruses start out killing 100% of their hosts and then slowly become
>something a little less deadly or is it the other way around?
Well, if they kill 100% of their hosts, that's pretty much the end of the
story there. But the concept of high virulence modulating over time is
a popular one, and I believe there is a little support for it. The
example of myxomavirus in Australian rabbits, if I understand it
correctly, worked that way (though it's as much a case of the host
adapting as the virus adapting, I think).
But I doubt that this is more than a rule of thumb, because there are
examples of viruses which remain highly virulent. Rabies, for example,
is *much* more virulent than Ebolavirus - I think there are 5 people who
have recovered from rabies, and there are tens of thousands of cases per
year - and shows no signs of abating. Smallpox was around for a long
time and, as far as I know, didn't ever become less virulent. Same with
polio. There are probably examples of viruses which start out mild and
evolve to increasing virulence, as well, though none are occuring to me
right now.
The concept that pathogens and their hosts evolve to a mutually
tolerant relationship has been around for a long time, and is clearly
overstated. That approach is just one of the long-term stable strategies
for a pathogen.
Ian
--
Ian York (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-3921 Fax (617)-632-2627
