I just wanted to make a short comment on the discussion that brought flu
in as an example. I don't think you can place viruses into a specific
host-parasite relationship that says that the virus will "evolve" in one
direction or the other. Mostly because you are not looking at anything
close to what we have known as "evolution" or species differentiation.
While virus adaptation to hosts certainly uses similar basic mechanisms
namely nucleotide change followed by selective pressure it is occuring at
such a rate and with so many fewer external variables than evolution of
higher organisms that it sort of falls into its own category. Attempting
to place behavioral characteristics on a virus or virus populations like
you would say a finch population responding to environment variables,
really stretches the imagination I think. My point is that in
considering the adaptation of virus to hosts I don't believe a set
paradigm will evolve. Adaptation of a mouse virus to a rabbit host for
example may involve a different set of variables and go in a completely
different direction (virulence wise) than say adaptation of a monkey
virus to humans. With regard to the flu pandemic of 1918, theories
abound as to the mechanisms of development of pathogenicity, but in
reality given the mutation rate, the reassortment rate of its 8 RNA
segments and particularly given the relatively SHORT period of time which
we have been able to track the virus molecularly, we could never have a
similar pandemic, or it could be starting tomorrow!
Mike Perdue
SEPRL
mperdue at asrr.arsusda.gov
