From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: sci.med
Subject: Re: The common cold
Date: 20 Sep 1998 23:39:45 GMT

In <01bde4cd$66b66520$5e947dc2@686> "Frank McGuire"
<fmaguire@indigo.ie> writes:

>For many years doctors and scientists have been seeking a cure
>for the common cold without success.
>It is my view that the common cold is not in fact a 'disease' but a
>natural mechanism for the body to discharge waste substances and
>bolster the immune system.
>Hence the application of rigorous scientific analysis to a problem
>which is not in fact a problem(to nature!) will not yield meaningful
>results.
>Any comments?


   It's long been an observation by men on ship that after a month out
of port there are no more colds.  Not till they make port again do more
colds start.

   Now: let's see you reconcile this with your point of view.  It's
easy to explain it with the infectious disease model:  By a few weeks
out of port, everyone has been exposed to every cold virus that
everyone has.

   After that you can explain the many experiments in which people have
been infected by common cold viruses, in order to study the disease.


                                     Steve Harris, M.D.

From: Ian A. York
Subject: Re: When is Common Cold Contagious?
Date: Dec 29 1996
Newsgroups: sci.med

In article <5a5vqq$k9n@herald.concentric.net>,
Chet Day <chetday@concentric.net> wrote:

>Are you saying a rhinovirus causes the common cold? Is it the only
>recognized cause of colds?

There are several virus families which cause the symptoms we call "the
common cold".  These include rhinoviruses, adenoviruses, coronaviruses,
and orthomyxoviruses and paramyxoviruses.  (If it seems strange to have so
many viruses causing "one disease", you should consider that the symptoms
of a cold are fairly non-specific - after all, the nose and throat can
only react in so many ways when they're infected; it would be asking a bit
much for a nose to, say, turn green for rhinoviruses and blue for
adenoviruses, when all it wants to do is get the virus out of there.) 

Of these virus families, rhinoviruses are the most common causes of colds;
but the difference is not all that spectacular.  Rhinoviruses probably
cause somewhere between a third and one half of colds.  Adenoviruses and
coronaviruses probably cause most of the rest, but there are also a fairly
large number whose cause can't be determined exactly.

For all these viruses, but especially for rhinoviruses, the colds are not
caused by a single species of virus.  Instead each is a family of viruses
with many members - rhinoviruses have over 100 different subtypes,
adenoviruses have close to 50, although not all cause cold-like symptoms.

>If only 50% of the people who get a shot of rhinovirus up the nose get
>a cold, I don't understand how one can conclude that colds are
>therefore contagious. Does the medical model use the 50% of a given
>sample to conclude that something is contagious?

I think you don't understand "contagious".  In fact 50% infection is quite
high for any contagious disease.  For any contagious disease, the
probability of the next individual getting infected depends on the agent
itself, plus the host factors (are you immune?  Are you stressed?  Do you
have cuts, scratches?  Are you already infected with another virus, which
might weaken the immune response or might concentrate it in the
appropriate area?) and the environmental factors (is it humid, so the
virus might survive longer?)  The bottom line is that most contagious
diseases are much, much less than 50% contagious.

It's far too simplistic to say (as Koch suggested, over 100 years ago) 
that an infectious agent must always cause the infection when given to a
host.  Things just don't work that way.

>How contagious are colds for folks who don't get a nasal injection of
>the rhinovirus virus?

About 50% in a family setting as well.

>If the virus is truly contagious, how come 50% who get the shot up the
>nose don't get a cold?

Perhaps they've already been exposed to the virus and are immune.  Perhaps
they don't have microscopic cuts in their nasal mucosa.  Perhaps they have
an abundant crop of nasal hair, which filtered out the aerosol before it
could do any damage.  Perhaps the others have been in dry air and damaged
their nasal mucosa.  Perhaps the others have recently had another virus
infection, too low-level to notice, which has left the cilia in the throat
mildly damaged.  Maybe due to stress their non-specific immune response is
weakened - or maybe due to stress the non-specific response is heightened.
There's a list of probably a thousand, or thousands of, factors which all
kick in to some greater or lesser degree. 

The whole field of viral pathogenesis is complicated and, frankly, not
well understood.  Of course, since you're looking at an end-result that's
the product of three fantastically complex systems (the virus, the host in
general, and the environment in general) it's probably more surprising
that anything is understood about it. 

Ian
-- 
      Ian York   (iayork@panix.com)  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England

From: Ian A. York
Subject: Re: Sputum samples for bronchial infection
Date: Dec 03 1996
Newsgroups: sci.med

In article <32a3dbe0.8544352@news.annex.com>,
Daniel Prince <neutrino@annex.com> wrote:

>iayork@panix.com (Ian A. York) wrote:
>
>>You wait it out, and treat the symptoms.  If you have a *persistent*
>>problem, it almost certainly is *not* a viral problem, because a
>>characteristic of the viral problems is that they are *not* persistent.  
>
>What about HIV and chronic viral hepatitis?  If those viral diseases
>can last for years or even decades why couldn't a viral bronchitis
>last for months or years?

It's a common error to generalize about "viruses".  There's no such thing
as a typical virus.  Knowing the behaviour of one virus does not allow you
to predict the behaviour of other viruses - even of closely related ones,
never mind unrelated viruses.  (And "unrelated" for viruses means *really*
unrelated - the differences between hepatitis B virus, rhinovirus, and
cytomegalovirus are *much* greater than the differences between me and a
redwood tree.)

What I'm trying to say is that I'm not trying to claim that, in theory, a
viral bronchitis (or rhinitis or pneumonia) *could not* be persistent.
(Take a moment to review those triple negatives.)  What I am saying is
that human viral causes of bronchitis (and rhinitis and pneumonia) *are
not* persistent pathogens.  It's pointless trying to extrapolate from hep
B to rhinovirus; all it lets you do is say that theoretically it could be
the case.  It tells you nothing about what *is* the case.

The closest to a persistent bronchial virus in humans would be the
adenovirus family.  Adenoviruses cause, among other things (and depending
on many factors) respiratory tract disease ranging from no symptoms (most
common) to typical cold symptoms to severe pneumonia (mainly in
immunodeficient people).  Although the *disease* caused by adenoviruses is
generally self-limiting and of short duration, the virus is pretty good at
persisting for long periods - months - even after the symptoms are
resolved.  But this isn't an exception to my statement that in humans
respiratory viruses cause short-lived disease, because the virus doesn't
cause the disease in the persistent phase.  (Adenoviruses were first
identified, in the '50's, by isolating a virus from the adenoids of a
*healthy* individual.) 

Epstein-Barr virus can also cause pneumonia, in rare circumstances, and
it's a persistent virus; but again the pneumonia per se isn't persistent. 
(It's also very rare, and I don't think there's been any cases of
bronchitis associated with EBV.)  There are a handful of other persistent
viruses that can very rarely, and mainly in the immune compromised, cause
respiratory diseases.  It's been suggested that respiratory syncytial
virus can cause persistent respiratory disease in humans, but the evidence
for this is is pretty weak, and it seems most likely that this is at most
a rare occurence - most RSV disease resolves pretty quickly.

So to summmarize, when we're talking about upper respiratory disease in
humans, if it persists for more than, oh, say, a week or ten days, you're
very unlikely to be dealing with a single viral infection.  

Ian

-- 
      Ian York   (iayork@panix.com)  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England