Re: Evolution and Bacteria


Stanley Friesen wrote:
> sharon@xxxxxxxxxxxxxxxxxxxxx wrote:
>
> >Add Hepatitis C to the list, I knew of somebody who had contracted that
> >virus, and he told me it could eventually lead to liver disease --these
> >are permanent in the blood/body fluids is my understanding?
>
> If it is a retro-virus, yes, it usually is.

Hepatitis C is a flavivirus and is a positive (coding) strand RNA virus
that replicates by use of an RNA-directed RNA polymerase. It is not a
retrovirus. There is no integrated DNA form that I know of. Chronic
(as opposed to acute) infection is poorly understood, but probably
involves low-level replication rather than integration. In this it is
similar to herpes viruses (which are dsDNA viruses that can lay around
in a cryptic state with occassional flares). Which is why there is the
joke about the difference between herpes and true love (ans: herpes is
forever).

Hepatitis B virus, however, does have many similarities to retroviruses
in its mode of replication, even though it spreads as a DNA virus.

Hepatitis A is an RNA virus (not a retrovirus) and only seems to cause
acute disease.

Virus replication and genomes are the most diverse in biosphere, with
dsDNA, ssDNA, ss(+)RNA, ss(-)RNA, and dsRNA forms with replication that
is RNA only, DNA only, and switch-hitters of various kinds. There are
even replicative entities (viroids) that are highly ds-like RNAs (but
topologically a ssRNA circle that anneals to itself) which encode no
proteins whatsoever. That is in addition to satellite (parasitic)
viruses that require other viruses to replicate.

> What retro-viruses often do
> is insert themselves into the host's own chromosomes. Once this has
> happened there is pretty much no way to eliminate it without killing the
> host.

Not quite true. Sometimes there are viral surface antigens that can be
attacked. But it is quite clear that the viruses that do engage in
chronic infection do so because it, from their viewpoint, is
selectively advantageous. Most HepC and/or HepB infections are spread
from carriers rather than people who only have the accute infection.

> >I suppose that would be a lot of work --mapping the genome and figuring
> >out how to genetically modify it where the virus itself would destroy
> >or neutralize the ill effects of the virus. Lots of money, or
> >completely impossible?
> >
> I was actually thinking more along the lines of deliberately selecting
> for less harmful forms. The problem with the genetic engineering is
> that the engineered form might not compete well with the wild form, so
> would do little good. One would need a very aggressive engineered mild
> form that corrupted the wild form as well.
>
> --
> The peace of God be with you.
>
> Stanley Friesen

.

Relevant Pages

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