From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Tue May 13 2003 - 19:14:16 MDT
On Tue, 13 May 2003, Mike Lorrey wrote:
> I have seen reports claiming that the genome of SARS is very stable,
> far more stable than cold or flu virii. If so, then a vaccine or earned
> immunity should be long lasting. How long is a good question.
I'm going to inject some hard-core virology into this discussion
so we may be dealing with some hard core data and not speculation.
Cold virus: A picornaviridae (a RNA virus) of the subtype Rhinovirus
(cold viruses) which have over 100 known serotypes -- i.e. different
variants that can evade ones existing immunological protection developed
due to prior infections. Bottom line -- until you have caught over
100 colds and developed an immune response against them you are
vulnerable. Their variability is one of the major reasons that a
"cold vaccine" is extremely difficult.
[For more info: See Fields Virology, Chapters 20: Picornaviridae
and Chapter 22: Rhinoviruses].
Flu (influenza) Virus:
Flu is also a RNA virus classified as an orthomyxoviridae. It
is separate from all other known viruses in that it has a
multi-segmented genome (i.e. its genomic program can exist
on 8-10 separate pieces of RNA). This is problematic because
there are strains of Flu/Influenza that infect a variety
of other species (chickens, pigs, etc.) and an intermixing
of some combination of the common human strain with some
less common animal strain may create a strain of Flu/Influenza
that is particularly dangerous -- this is why the flu vaccines
change every year.
[For more info: See Fields Virology, Chapters 39 & 40
Orthomyxovirdae and Their Replication and Orthomyxoviruses]
So SARS doesn't easily match either "cold" viruses or
"flu" viruses.
> > When will an effective vaccine be available?
>
> Considering that its genome is now sequenced, and teams are working on
> it, I think that getting a vaccine shouldn't take more than a year or
> two.
If it does indeed turn out to be stable, this is not an unreasonable
estimate. One of the questions that may need to be resolved is whether
it develops into a number of serotypes like the cold virus -- in which
case the vaccine alternative may be more difficult.
> > Is the fatality rate due to direct action by the virus, or due to
> > ancillary infections (that might be controlled with antibiotics)?
>
> Since the fatality rate is most pronounced with those over 50
> (currently 55%), and that severity tends to be caused by the body's
> reaction to the virus, I don't think that anti-biotics would help,
This is accurate. Anti-biotics are of little or no use. One of the
major problems seems to be an "over-reaction" on the part of the body
to the infection.
> though immunosuppressants might be a strategy worth pursuing, applied
> after the infection has peaked but while the immune system is ramping
> up its hyper reaction that causes deaths.
It would seem this is the right approach -- but I haven't seen any
clear clinical data regarding what "arms" of the immune system response
one would want to selectively constrain. It is a very sticky problem.
Robert
Refs:
Fields Virology, Vols. 1 & 2., 2nd Ed. Raven Press, NY, (1990).
FYI: if someone is talking about virology and they aren't citing this
ref then it is highly questionable whether they know what they are
speaking about.
This archive was generated by hypermail 2.1.5 : Tue May 13 2003 - 19:25:36 MDT