Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!turpin
From: turpin@cs.utexas.edu (Russell Turpin)
Newsgroups: sci.bio
Subject: Re: What's the Why and How of Mosquito Bites?
Summary: The nature of epidemiological studies.
Message-ID: <6733@cs.utexas.edu>
Date: 21 Aug 89 20:21:58 GMT
References: <5399@mtgzy.att.com> <4948@tank.uchicago.edu> <9263@chinet.chi.il.us> <9297@chinet.chi.il.us>
Organization: U. Texas CS Dept., Austin, Texas
Lines: 72

ARF says: 

> Mosquito transmission does not show up in epidemiological  
> studies because of the absurdity of asking every AIDS  
> victim:  "Have you ever been bitten by a mosquito?" 

Which shows that ARF understands very little about epidemiology.
While individual case histories are very important, many
questions can be answered by studying evidence of a more
statistical nature.  What is the age distribution of those
infected?  In what regions is the disease most prevalent?  Does
infection incidence vary with season?  What socio-economic
factors correlate with infection?  How do these factors correlate
with exposure to possible vectors? 

When statistics of these kinds are combined with information from
case histories, it is possible to learn a lot about the nature of
transmission of a disease.  A mosquito vectored disease displays
particular statistical patterns in these areas.  These patterns
will show up even if it is a minor mode of transmission.  If such
patterns don't show up at all, it's because mosquito transmission
is extremely rare.  One doesn't have to ask people "Have you ever
been bitten by a striped mosquito" in order to find out that a
disease is transmitted by a particular kind of mosquito. 

As I previously noted, such knowledge, like the evidence, is
statistical in nature.  No one can prove that mosquito
transmission of HIV is impossible or has never happened.  Of
course, the same can be said for syphillis.  But if it occurs, it
is so rare that the epidemiological evidence does not show it.

Again, the "Scientific American" issue on AIDS had an article on
its epidemiology with references to various studies, and these
references will themselves have references.  If you want to study
this matter in depth, you can find out precisely what research
has been done and by whom and how thoroughly, but don't expect
people on the net to do your library work for you.  Maybe the
epidemiological research is sloppy or insufficient, and you would
be doing us all a favor by doing more, better.  Go to it.  We would
all welcome better, surer knowledge on this disease. 

If mosquito transmission of HIV is rare, we will never know just
how improbable it is.  To know this, one would have to let a
cloud of mosquitos take partial meals from a group of people who
are HIV positive, transfer the mosquitos into an auditorium in
which there were a hundred thousand people without HIV exposure,
have these subjects slap the mosquitos that bit them, track them
for several months to see who seroconverted, and make sure that
those who did were not exposed by other means.  (If none
seroconverted from slapping mosquitos, that still doesn't mean it
is impossible.  Perhaps if one used a million subjects ...)  Even
excluding ethical considerations, such an experiment is clearly
impractical, and the results would not be very helpful.  What,
pray tell, would you do with a fact like "If an anopholes g.
takes a partial meal from an HIV positive person and within ten
minutes bites an HIV negative subject who then slaps the mosquito
and smears its blood over the subject's skin and fails to wash it
away for the next half hour, then the subject's odds of
seroconverting is .00000167"? 

Like I said before, if the risk worries you, don't slap that
mosquito.  Personally, when I'm out and about I worry much more
about water moccasins.  If I were to worry about mosquito
vectored diseases, it would be dengue fever (of which we had a
few cases in Texas some years ago) and equine encephalitis.  You
don't have to slap that mosquito to get these, and they may kill
you quicker to boot! 

Are you any relation to ALF?  You two seem to think on the same
wavelength.

Russell