Question re: rabies

Steven Poet poets at ccmail.orst.edu
Mon Sep 11 12:19:40 EST 1995


The most obvious answer to the quarantine question is the fact that
rabies is virtually 100% fatal in most mammals, humans included.  All
diagnostic tests have false negative results and false positive results.
The risk of a false negative for rabies is unacceptable.  Using
quarantine and observation for suspect animals is the only way to be
sure rabies transmission will not occur.  I believe 6 months is the
quarantine period for unvaccinated animals suspected of exposure.

york at mbcrr.dfci.harvard.edu (Ian A. York) wrote:
>
> 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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