(Fwd) Re: (Fwd) Re: Ok, so the CDC has confirmed..and other th

[bhjelle at unm.edu]

In article <70EC521BBF at prl.pulmonary.ubc.ca>,
 <DANDERSON at PRL.PULMONARY.UBC.CA> wrote:
>
>>> "This alleged instability of RNA viruses is one of the
>>> most misunderstood phenomena, even among some virologists."
>> 
>> An example of just how stable RNA viruses can be is Rubella.  Strains 
>> of this virus have been passaged in different laboratories for years 
>> with no genetic changes, unless forced.
>> 
>najital at rockvax.rockefeller.edu (Lyle Najita) replyed:
>
(lots deleted)
>
>These data, suggest the ability to mutate, increasing or decreasing 
>virulence and tissue tropism, is virus AND host sensitive, and is 
>probably dependent upon host and virus replication proteins.  What 
>lends fidelity to the viral replication complex?
>
Evolutionary biologists make a distinction between incident
mutations and those that become "fixed" in a population.
To become fixed mutations must be nearly neutral or advantageous.
When you sequence viruses from a host or cell line, you are
dealing with a predominant form that has a selective advantage
or is at least neutral. This is not the same as enforced fidelity
but can appear the same when you look only at the predominant form
of the sequence.

I agree with you that it is the host that determines the optimal
viral genotype. We have looked at viral genotypes (hantaviruses)
associated with a particular host over 20 years time span.
1975 forms are essentially identical to present-day forms.
There is also no alteration that occurs in the course of
an acute human infection, at least in regions we have examined.

Brian