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BSE questions

Joao Vasconcelos Costa jcosta at pen.gulbenkian.pt
Fri Mar 22 10:48:18 EST 1996

john brooks wrote:
> I hope these are appropriate questions for this group - having
> trawled through all 10000-plus groups looking for appropriate
> keywords, I ended up with only one candidate!
> I further hope that these issues have not been covered with
> recently.
> Note that whilst reasonably well-informed, I am not a virologist.
> -       wozza prion? Yup, I know it's a protein and presumably
> capable of self-replication, but what about other similarities /
> differences to viruses?

Similarities: prions are infectious, they have strain characteristics
(in what concerns host range, pathology, kinetics of infection, etc)
and a pathogeny pattern (i.e. the way the agent spreads in the organism
until it reaches the main target).
Differences: no viral-like particles, apparently no nucleic acid.
This quite schematic but I think touches the main points.
> -       are scrapie and BSE caused by identical prions? if so, why
> are we only panicking about beef? is the cause - effect
> relationship for a prion and BSE fully established?

1st question: No. The sequence of the PrP normal proteins of sheep and 
cows is similar but not exactly the same. The BSE agent is a altered 
version of the cow PrP protein. This change was much probably induced by 
the scrapie agent but the BSE agent is no longer the original 
contaminating scrapie agent.
2nd: I think that the same precautions should be taken about sheep and 
cow brain and nervous tissues. Personally, I don't think there is any 
reason to panick about beef. All evidence shows that clean muscle is
completely devoided of infectivity, even when large amounts are inocu-
lated parenterically. The oral route is even much more inefficient for
transmission. The only doubt I have is about processed meat (hamburgers,
sausiges, spagetti meat sauces, etc) that may be contaminated with
potentially infective tissues (brain, spleen, thymus, intestinal lymph
3rd: Undoubtedly! The disease can be transmited experimentally to
laboratory rodents. 
> -       are cattle susceptible to BSE infection due to the
> inability of their digestive systems to digest proteins? IOW, do
> complete proteins 'leak out' into the blood stream as such, rather
> than being disassembled into amino acids first?

The same happens to many viruses that can penetrate the digestive mucosa
without being destroyed by the digestive enzymes.

*****   Instituto Gulbenkian de Ciencia - Oeiras, Portugal
*****   mailto:jcosta at pen.gulbenkian.pt
*****   http://www.pen.gulbenkian.pt/v2/jvc.html

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