Question re: rabies

Ian A. York york at mbcrr.dfci.harvard.edu
Mon Sep 11 10:38:35 EST 1995


In article <Laurie_McDonough-110995091901 at srquadra.geo.brown.edu>,
Laurie McDonough <Laurie_McDonough at brown.edu> wrote:
>Would someone please explain to me why no test for rabies has been
>developed?  It would seem that an antibody test could be easily developed. 

Why does it seem 'obvious'?  I don't know for sure, but I'm very 
skeptical that many cases of rabies will show any antibody response.  The 
virus rapidly enters nerve cells, and spreads by cell-to-cell contact, 
and therefore (1) remains sequestered in an immunologically privileged 
site (the nervous system) and (2) doesn't enter the circulation or other 
regions to become accessible to the immune response.  Further, the 
infection can progress more rapidly than a primary immune response can 
develop.  

If you mean by "antibody test" an "antigen test" (that is, if you want to 
make a test that uses antibodies to detect the rabies antigen, such as an 
elisa or western blot) then you have an even greater problem, which is 
that the site of virus replication is not exactly easily reached.  In 
fact the test that's used is such an antigen tesat, but since it has to 
be done on nervous tissue the animal in question must be killed first.  
Unless you can suggest a useful method of testing the brain (I think it's 
the negri bodies in the hyothalamus that are checked) in a non-fatal way.

>Obviously, if one had an expensive animal, say a AKC champion dog, which
>got into a tangle with a wild animal, a test to see if the dog had
>contracted rabies would be much more efficient and less expensive than
>quarantine.

It would only be 'more efficient' if it had any chance of working.

>I have also been told that the incubation period for rabies in cats and
>dogs ranges from six months to several years, is this true?

Nonsense.  The incubation period can range from a few days to a few 
months.  One of the most important factors is the area that's bitten: if 
the bite is very close to the brain (eg on the face) the infection can 
progress more rapidly than if the infection is distal and the virus needs 
to pass through the peripheral nerves first.

I don't know the upper end of the incubation period; I believe cases thta 
have taken 6 months or so from exposure to clinical signs have been 
documented.  I doubt there is anything much longer than that.

Ian
-- 
Ian York   (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-3921     Fax  (617)-632-2627




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