The publicity surrounding the recent genotype susceptibility is puzzling
me.
As I understand it, someone died not of vCJD but something completely
different yet vCJD prions were found in his lymph nodes and spleen. He
had had a transfusion - presumably quite a long time ago - from someone
who subsequently died of vCJD in 1999. The complication is that the
patient that recently died is of a different genotype to that for which
susceptibility to vCJD is thought and which comprises about 37% of the
population.
A very simple sum would indicate that the probability of contracting vCJD
from a transfusion is the Sum (prob. the blood infected * susceptibility
of patient) over all genotypes. Multiply this by the probability of a
transfusion occurring at all (<<1 per year) to get an overall figure.
It may have been assumed that only 1 genotype is susceptible but this
cannot exclude much lower susceptibility. Frailty is never absolute.
Since the susceptibility of the 63% must be a lot lower than that of the
37% (appprox 63/37/142 or about 0.12% because there have been 142
susceptible deaths and 1 unsusceptible non-death so far), I am wondering
what all the fuss is about. Yes, it may blow a few theories out of the
water - those that were absolutely dependent on only 37% of the population
being at risk - but it will make very little difference given all the
uncertainties in incubation times, infection times etc. It is as if there
will be a small increase - or a slower decrease - but I don't see that it
makes a lot of difference to the overall prediction.
I don't know how many transfusions are carried out per year but that must
be a lot less than 37% of the population.
With all the variation in infection and incubation times, it was never
likely that this epidemic would be over in a few years so what has been
the change? There are so many distributions mixed together that the death
rate was always likely to be pretty flat and therefore prolonged.
My underlying question is - what is the underlying epidemiological reason
for the explosion of interest? Or is it just trying to keep the issue
alive and possibly increasing research funding? I am not averse at all to
maintaining and increasing the research funding - the more money put into
science the better - but I don't think it warrants headline scare stories.
The Today program - that authority to which we all wake up - ran it as a
top story.
Am I completely wrong about this? What does the epidemiology say?
John
John Logsdon "Try to make things as simple
Quantex Research Ltd, Manchester UK as possible but not simpler"
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+44(0)161 445 4951/G:+44(0)7717758675 www.quantex-research.com
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