From: sbharris@ix.netcom.com(Steven B. Harris)
Subject: Re: Very basic questions regarding the "disappearance" of diseases....
Date: 28 May 1997
Newsgroups: sci.med

In <19970527213500.RAA04851@ladder02.news.aol.com> g03090103@aol.com
(G03090103) writes:

>Would someone well-versed in virology please answer a question that's
>been bothering me?  Certain viral diseases have been declared
>"eradicated" or "virtually eradicted" (e.g., smallpox and polio); medical
>authorities have claimed that it's possible to eliminate others as well
>via the widespread (increased) use of vaccines.  From where did these
>viruses arise?  Did they originate *in* humans?  (How, if it can be
>briefly explained in layman's terms?) Assuming they didn't, and were
>transmitted to humans through a vector organism, how can we know for
>certain that they have been/can be positively eradicated--that they won't
>reappear in the future?


   Many of the most virulent human viral disease probably WERE
transfered from animals to humans fairly recently.  An example is AIDS.
Others that haven't quite made the transfer, but keep trying, are Ebola
and rabies.  Still other diseases are transfered routinely between
animals and humans (influenza) and for these, there is no hope at all
of wiping out the disease with vaccination.  Finally, it may be that a
few very old diseases (TB, many parasitic worms) have been with people
as long as humans have been humans as a species (ie, they evolved with
us).  But it's hard to say for sure.

   It's hard for a virus to make the interspecies transfer, very often,
and it's a ticklish things for it to survive a few generations until it
can adapt to its new host (Ebola and rabies, again, as examples).  In
that time, it's vulnerable.  If you can wipe out the adapted form of
the virus for the human host, then the old animal form needs to make
the jump again, and survive, before the disease comes back.  No
garantee that won't happen, but for many viruses it's hard.  And worth
the effort in vaccination to get to there.  If we wipe out AIDS in
humans, it won't come back again until somebody is bitten by a chimp or
a monkey, and then spreads it.  But next time, precautions can be
taken, as in rabies.





>A related question....  Few medical personnel deny that immunity
>conferred by vaccines "wears off" over time (hence the need for
>"boosters"). We've already (mid-1980s through the early 1990s) witnessed
>outbreaks of measles and mumps on various college and university
>campuses, outbreaks that have prompted many, if not most, schools to
>require matriculating students to provide proof of re-vaccination.  What
>about the vast numbers of young adults who do not attend college (and who
>do not join the military)? Isn't it conceivable that they form a rather
>large pool of "susceptibles" who can contract a given disease and then
>transmit it to others, including those 10-15% of vaccinated chidren in
>whom the vaccine didn't "take"?


   Comment:  Yep.  Pertussis (whooping caugh) is a case in point.  You
do the best you can.

    There are some diseases, BTW, which are much worse in adults, like
chickenpox and mono, and sanitation just makes the incidence of these
diseases (as severe illnesses) increase.  Polio, for instance, was not
really a problem until about 100 years ago, when sanitation improved
(that's one of the things that makes me laugh at the anti-vaccine nuts,
who claim that sanitation was responsible for the decline of polio;
exactly the opposite is true if you're talking about clinical polio).
Polio doesn't harm most infants that get it, but it's worse for adults.
The quintessential American polio victim is someone like the patrician
FDR, who spent his childhood isolated from other kids, and didn't get
polio until the age of 39, after a little political glad-handing at a
boy scout camp.

                                            Steve Harris, M.D.