BSE versus Creutzveld-Jacobs-syndrome

[Joao Vasconcelos Costa]

bhjelle at unm.edu wrote:
> 
> In article <ns10005-3003961715450001 at mac17.vet.cam.ac.uk>,
> Nigel Smith <ns10005 at cam.ac.uk> wrote:
> >In article <4jhafv$1dpq at pegasus.unm.edu>, bhjelle at unm.edu wrote:
> >
> >> of BSE. In the laboratory, BSE has been transmitted to mice,
> >> goats and sheep via the oral route (see http://www.airtime
> >> co.uk/bse/tse.htm.#immunity). BSE can be transmitted into
> >> transgenic mice bearing human PrP and produces human PrPSc.
> >
> >Well, from that link:
> 
> (quote deleted)
> >
> >So, not a mention of an oral route there, then.
> >IIRC, the *test* for BSE requires direct injection into a mouse, since the
> >is no contagion via the oral route.
> 
> Sigh. I'll give you a more direct link to the statements
> and some references.
> 
> http://www.airtime.co.uk/bse/tse.htm.#bse
> 
> references: Annals NY Acad Sci 1994; pg 300 (sorry,
> forgot to write down volume number).
> 
> J Gen Virol 1994 vol 75, 2151 (experimental oral
> transmission of BSE to mink). I'm not an expert on
> mammalian evolution, but I would speculate that
> there is about as much difference between a cow
> and a mink as there is between a cow and a man.
> The point is that BSE can cross some rather substantial
> species boundaries (by oral route), from ruminants into
> animals of the orders Carnivora and Rodentia.
> Given that humans and
> apes are well-known to be subject to spongiform
> encephalopathy, is it so amazing that oral
> transmission can also occur between cattle and
> primates?

------------
Theoretically, it is possible. The homology between the PrP genes of
sheep and cow is 94.3% (95.5% if you consider the related aminoacids)
and the homology between the human and bovine genes is of 87.9 (93.9%).
Not an impressive difference in gene relationships.
But my point was different. No infectivity could be found in muscle (in-
cluding, of course, the nerve endings present in the muscle) after 
intracerebral inoculation into mice. If we take in acount that the oral
route in prion transmission is at least 10^3 less efficient, the risk
of human infection by ingestion of meat is virtually none.
Much different in risk, of course, is eating bovine brain or even, at
lower risk, spleen or thymus.
------------
 
> >> As for the risk from sheep and pigs, I would say that if
> >> we had 160,000 cases of scrapie in sheep or porcine
> >> spongiform encephalopathy, it should be regarded with the
> >> same concern as the bovine epidemic.
> >
> >Scrapie has been endemic in sheep around the world for more than 200
> >years. I would be *very* surprised if there hadn't been 160,000 cases by
> >now.
> 
> Since scrapie disease is very poorly reported and
> its incidence is largely unknown, that becomes a very
> uncontestable statement. However, even if there have
> been 160,000 cases over 200 years (very doubtful),
> how does that compare to 160,000 cases over 10
> years in a very small area of the world? Answer:
> it doesn't.
> 
> Just a reminder: 90% of human CJD is "sporadic". If
> 10 or 100 cases were actually caused by eating contaminated
> sheep, who would be the wiser?

------------
There are countries, like mine, that fortunately never had scrapie.
However, the incidence of CJD is the same as everywhere else.
------------

> 
> >> I would challenge you to convince me that the operation of
> >> slaughterhouses could be modified to prevent low-level
> >> contamination of meat with neural tissue, and still have
> >> an economically viable operation.
> >
> >And I challenge you to find any record of any contamination in meat for
> >sale. There has not been a single case where joint of beef has been found
> >to contain the prions believed to be the agent of transmission.
> >
> Again, a very easy statement to make and hard to
> refute. There is no DNA or RNA in the prion, so some
> of the most sensitive methods available (PCR, LCR, etc)
> are not available. Infected animals do no raise antibodies
> in the course of disease. No tissue culture isolation
> has any significant sensitivity. This is all *very*
> similar to what we had available to detect HIV in
> the early days of transfusion-associated AIDS (1983-
> 1984).

-------------
The assays for infectivity in muscle tissue have been done on tissues
from *sick* animals. So, your argument about the difficulty in diagnosis
is not pertinent.


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