Prions? CJD/BSE Connection...

David Cassarino dsc9w at avery.med.Virginia.EDU
Sat Apr 6 16:07:18 EST 1996


shaunc at alumnae.caltech.edu  writes:
> dsc9w at avery.med.Virginia.EDU (David Cassarino) writes:
> 
> >> >Apart from pathological cases or examples in extremis (e.g. the Andes 
> >> >plane crash) there is absolutely no evidence of 'normal' cannibalism 
> >> >anywhere on earth. The transmission of kuru is not by the eating of human 
> >> >brains but by the practice employed by those contracting this disaease of 
> >> >exhuming their dead after a period of burial, and emptying the cranial 
> >> >cavity of brain material by hand; the disease being transmitted through 
> >> >small cuts in the skin.
> >> 
> >The only way to get CJD from ingestion of prions is via
> >innoculation (ie, if you have cuts in your mouth or
> >esophagus).  As proteins, prions are degraded to AAs in the stomach,
> >and thus do not pose a significant threat in the normal GI
> >system.  
> 
> Not true.  CJD can be transmitted through both parenteral and oral routes.
> Prions are remarkably resistant to most agents, chemical and physical, and
> are noteworthy for being protease-resistant, which means that they would
> _not_ be digested in the stomach.
> 
> ********************************************************
> * Shaun D. Carstairs                                   *
> * Uniformed Services University of the Health Sciences *
> * shaunc at alumni.caltech.edu                            *
> * s98carstairs at usuhsb.usuhs.mil                        *
> ********************************************************

The only documented cases of transmissible CJD have been
through innoculation.  Animal experiments, as far as I know,
have repeatedly shown that PrPsc can be transmitted parenterally
(IV, innoculation), but have never shown oral transmission.
 You are right that the Prpsc is partially protease resistant,
but part of the protein supposedly required for infectivity is
protease susceptible (Mandell, Infectious Diseases, 95).
Even if some proteins escape digestion in the stomach and small
intestine, they will most likely not be absorbed as the SI
absorbs mostly AAs and peptides and a large molecule like this
(30kD) is highly unlikely to be absorbed intact.
  The likelihood of getting CJD from bovine prions, BTW, is
also highly unlikely because of the significant sequence
differences between the human and bovine forms (see Prosiner's
work).
-- 
David S. Cassarino              "The mind is not a vessel to be filled
MSTP 2nd Year                    but a fire to be kindled."               
UVA School of Medicine           -Plutarch
dsc9w at virginia.edu          



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