Prions? CJD/BSE Connection...

Shaun D. Carstairs shaunc at alumnae.caltech.edu
Sun Apr 7 16:44:06 EST 1996


dsc9w at avery.med.Virginia.EDU (David Cassarino) writes:
>> >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.
>> 
>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).

Again, not true.  Reference William N. Kelley's _Textbook of Internal
Medicine_ (2nd edition), "Creutzfeldt-Jakob Disease," p. 2219:

"Transmission can be effected by oral or parenteral inoculation but is
most efficient by intracerebral routes.  The incubation period is dependent
on the dose and route of inoculation and host genetics and may theoretically
exceed the life-span of the host."

As you stated, the prions will _most likely_ not be absorbed from the
small intestine.  However, on rare occasions this is not the case: 
macromolecular pinocytosis, while rare beyond the neonatal period, can
occasionally occur, as can direct molecular entry into the bloodstream
through small ulcerations in the intestinal mucosa.  Thus oral transmission
of CJD, while rare, is possible.

********************************************************
* Shaun D. Carstairs                                   *
* Uniformed Services University of the Health Sciences *
* shaunc at alumni.caltech.edu                            *
* s98carstairs at usuhsb.usuhs.mil                        *
********************************************************




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