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Subject: Re: Time to illness
Message-ID: <1991Jan16.204631.9402@cs.ucla.edu>
Date: 16 Jan 91 19:15:56 GMT
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liz@ai.mit.edu (Liz A. Highleyman) writes:
|> I was under the impression that the time between infection with HIV and
|> the development of illness was somewhere in the area of 5 years.  Yet
|> I have also heard that people who received transfusions of infected
|> blood (early in the epidemic) were known to get sick within a few months.
|> How can this be?  Is it taking longer and longer for people to develop
|> OIs?  Does this indicate that HIV is perhaps becoming less virulent?

I had the opportunity to interact with a mathematical epidemiologist
this summer: she estimated the time from exposure to full-blown AIDS has
a standard half-life of about 8-10 years.  This means that at 8 years, 
half of the people exposed will have contracted full-blown AIDS.  At 16 
years, 3/4 will have contracted full-blown AIDS, etc.

I know of no documentation indicating that HIV is becoming less virulent.
It makes sense that a person who received a massive infusion of infected
blood might take less time to contract the full disease, than one who
was exposed through some other, less efficient transmission mode.
Furthermore, in the beginning years of the epidemic, no testing was done
of donated blood, so the likelihood of getting a transfusion containing
a raging infection might be higher.

Finally, however, it is a good rule of thumb that over many years, fatal
infectious agents evolve to something less virulent:  from an 
evolutionary standpoint, it isn't good policy to kill one's host.  
However, the number of years required to see this evolution will likely 
be large, especially in the case of HIV, which already takes a very long
time to kill the host.

____
\  /Dan Greening	IBM T.J.Watson Research Center	 NY (914) 784-7861
 \/ dgreen@ibm.com	Yorktown Heights, NY 10598-0704	 CA (213) 825-2266