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Old 26-04-2003, 01:23 PM
Oz
 
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Default UK vCJD October 2002

Gordon Couger writes

It wouldn't be bell shaped. I am exactly sure what the curve of an emerging
diseases looks like it would be different for each one, but the fear was
that it would be like growth curve of bacteria with a slow early phase and
very rapid log phase.


That's a pretty good description of what happened in cattle if you take
birth date and adjust for seasonality, up until the first MBM ban. Of
course it would have been bell shaped simply because there would have
been few if any unaffected cattle without the ban.

Other diseases have shown this kind of explosive out
break. So the early predictions have a very wide range of out comes and of
course the press picked up on the one that sold the most papers.


The fact that it resulted in substantial grants to the researchers had
nothing to do with the stories of course.

Fortunately humans appear to poor hosts for vCJD. It face cattle don't
appear to be very good hosts for it either.


So far only about 40% of the UK genotype seems to be susceptible (met-
met). Interestingly it's the genotype considered resistant to CJD. If
work on scrapie and sheep genetics is followed in humans then we ought
to expect little or none in the (not-met)(not-met) group (probably about
30% of the population) and considerably lower incidences in the
(met)(not-met) group (about 30%). GM mice with these genotypes did not
succumb to exposure to BSE (in the brain).

Since we do not know the exposure we do not know how susceptible humans
are. Cats, pigs and dogs in the UK had heavy exposure and the incidence
is small for cats, zero for dogs and pigs. I would point out that the
'species barrier' is misunderstood by many in that it is typically not a
total barrier but represents how hard it is to infect a species with a
particular prionic disease. Under extreme enough exposure (like
injecting it directly into the brain) most species can be infected by
most prionic diseases.

We do know for SURE that BSE is hugely less infective to humans than
human-strains of CJD. We know that invisibly microscopic traces of CJD
on stainless surgical implements can infect many subsequent people and
that post mortems on CJD patients carry a high risk of infection to
those doing the work. However thousands (probably tens of thousands) of
people, from farmers and vets, through abattoir workers, butchers,
knackers, renderers and hauliers are known for sure to have been
regularly exposed to high levels of known highly infectious material for
many years with not a single one of these groups so far succumbing to v-
CJD (although sooner of later it will happen).

Flat curves are good for vCJD declining would be better.


If we can get the data on dates of onset for this year (I'll probably
get the question asked in january) then I suspect the evidence will be
pretty clear, one way or the other. I have a horrible suspicion it's
going to match a flat curve. This would make me increasingly suspicious
that v-CJD is a low-incidence human CJD unrelated to BSE.

--
Oz
This post is worth absolutely nothing and is probably fallacious.
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