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From: B. Harris)
Subject: Re: Study Indicates AIDS Getting More Aggressive
Date: 26 Apr 1997

In <> (Get
Well) writes:

>"Study Indicates AIDS Getting More Aggressive"
>Reuters (04/24/97); Fox, Maggie
>     New research published in the British Medical Journal
>suggests that HIV may be getting more aggressive.  Italian
>researchers from the University of Turin studied 300 HIV-infected
>patients and found that those infected after 1989 have become
>sicker faster than those infected prior to that year.  They
>concluded that the virus could be mutating into stronger forms,
>making early screening all the more essential.  Moreover, they
>noted, AIDS experts may need to consider changing their treatment

    Such a study has to be taken with a grain of salt, in that we know
that the viral load of the person doing the infecting has some
influence on the rate at which the infectee gets sick.  This is
presumably an inoculum effect.  Early in an epidemic, infections are
more likely to be from people who have relatively low viral loads.
Later in an epidemic, after the epidemic has matured and is no longer
in log phase growth, the characteristics of the average transmitting
person change.  Simply stated, there are going to be a large fraction
of HIV positive people in the later states of infection in 1989 than
there were in 1984 or 1985 when things were first beginning.  The
people they infect are going to experience a different clinical course,
if what we understand about this disease is correct.   Really, you need
stats which control for the years of seropositivity of the transmitting
person, to get around this variable.

    It's certainly possible for AIDS to grow more agressive, but there
are limits here also.  No sexually transmitted disease which makes
people sick rapidly is going to win out against a strain which doesn't.
People don't like to have sex with people who are sick, and indeed,
many of the sexual attractant characteristics we as a species like
(good hair, skin, teeth, breath) are also markers of health, nutrition,
and freedom from parisitism.   Not a coincidence, from an evolutionary
point of view.  If your partner is chronically ill, that may say
something about his or her genetics, and thus about your offspring's
chance for survival.

   I recently read a pretty savage review of a popular book on
epidemics, in which the reviewer held that it is not true that epidemic
diseases grow more benign with time, due to evolutionary forces which
limit virulence.  The reviewer's counterexample was malaria.  Alas,
there is far less evolutionary pressure against virulence for
infectious organisms which are transmitted between people by an
intermediate vector.  Malaria doesn't care if you look like hell and
are too weak to walk-- the mosquito does the work, and doesn't require
an introduction to either party.  Sexually transmitted diseases don't
have this luxury.

                                              Steve Harris, M.D.

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